gst-plugins-rs/plugins/src/webrtcsink/imp.rs

use anyhow::Context;
use gst::glib;
use gst::prelude::*;
use gst::subclass::prelude::*;
use gst::{gst_debug, gst_error, gst_info, gst_log, gst_trace, gst_warning};
use gst_rtp::prelude::*;

use async_std::task;
use futures::prelude::*;

use anyhow::{anyhow, Error};
use once_cell::sync::Lazy;
use std::collections::HashMap;
use std::ops::Mul;
use std::sync::Mutex;

use super::utils::{make_element, StreamProducer};
use super::{WebRTCSinkCongestionControl, WebRTCSinkError, WebRTCSinkMitigationMode};
use crate::signaller::Signaller;
use std::collections::BTreeMap;

static CAT: Lazy<gst::DebugCategory> = Lazy::new(|| {
    gst::DebugCategory::new(
        "webrtcsink",
        gst::DebugColorFlags::empty(),
        Some("WebRTC sink"),
    )
});

const RTP_TWCC_URI: &str =
    "http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01";

const DEFAULT_STUN_SERVER: Option<&str> = Some("stun://stun.l.google.com:19302");
const DEFAULT_MIN_BITRATE: u32 = 1000;

/* I have found higher values to cause packet loss *somewhere* in
 * my local network, possibly related to chrome's pretty low UDP
 * buffer sizes */
const DEFAULT_MAX_BITRATE: u32 = 8192000;
const DEFAULT_CONGESTION_CONTROL: WebRTCSinkCongestionControl =
    WebRTCSinkCongestionControl::Homegrown;
const DEFAULT_DO_FEC: bool = true;
const DEFAULT_DO_RETRANSMISSION: bool = true;

/// User configuration
struct Settings {
    video_caps: gst::Caps,
    audio_caps: gst::Caps,
    turn_server: Option<String>,
    stun_server: Option<String>,
    cc_heuristic: WebRTCSinkCongestionControl,
    min_bitrate: u32,
    max_bitrate: u32,
    do_fec: bool,
    do_retransmission: bool,
}

/// Represents a codec we can offer
#[derive(Debug)]
struct Codec {
    is_video: bool,
    encoder: gst::ElementFactory,
    payloader: gst::ElementFactory,
    caps: gst::Caps,
    payload: i32,
}

/// Wrapper around our sink pads
#[derive(Debug, Clone)]
struct InputStream {
    sink_pad: gst::GhostPad,
    producer: Option<StreamProducer>,
    /// The (fixed) caps coming in
    in_caps: Option<gst::Caps>,
    /// The caps we will offer, as a set of fixed structures
    out_caps: Option<gst::Caps>,
    /// Pace input data
    clocksync: Option<gst::Element>,
}

/// Wrapper around webrtcbin pads
#[derive(Clone)]
struct WebRTCPad {
    pad: gst::Pad,
    /// The (fixed) caps of the corresponding input stream
    in_caps: gst::Caps,
    /// The m= line index in the SDP
    media_idx: u32,
    ssrc: u32,
    /// The name of the corresponding InputStream's sink_pad
    stream_name: String,
    /// The payload selected in the answer, None at first
    payload: Option<i32>,
}

/// Wrapper around GStreamer encoder element, keeps track of factory
/// name in order to provide a unified set / get bitrate API, also
/// tracks a raw capsfilter used to resize / decimate the input video
/// stream according to the bitrate, thresholds hardcoded for now
struct VideoEncoder {
    factory_name: String,
    codec_name: String,
    element: gst::Element,
    filter: gst::Element,
    halved_framerate: gst::Fraction,
    video_info: gst_video::VideoInfo,
    peer_id: String,
    mitigation_mode: WebRTCSinkMitigationMode,
    transceiver: gst_webrtc::WebRTCRTPTransceiver,
}

struct CongestionController {
    /// Overall bitrate target for all video streams.
    /// Hasn't been tested with multiple video streams, but
    /// current design is simply to divide bitrate equally.
    bitrate_ema: Option<f64>,
    /// Exponential moving average, updated when bitrate is
    /// decreased, discarded when increased again past last
    /// congestion window. Smoothing factor hardcoded.
    target_bitrate: i32,
    /// Exponentially weighted moving variance, recursively
    /// updated along with bitrate_ema. sqrt'd to obtain standard
    /// deviation, used to determine whether to increase bitrate
    /// additively or multiplicatively
    bitrate_emvar: f64,
    /// Used in additive mode to track last control time, influences
    /// calculation of added value according to gcc section 5.5
    last_update_time: Option<std::time::Instant>,
    /// For logging purposes
    peer_id: String,

    min_bitrate: u32,
    max_bitrate: u32,
}

#[derive(Debug)]
enum IncreaseType {
    /// Increase bitrate by value
    Additive(f64),
    /// Increase bitrate by factor
    Multiplicative(f64),
}

#[derive(Debug)]
enum CongestionControlOp {
    /// Don't update target bitrate
    Hold,
    /// Decrease target bitrate
    Decrease(f64),
    /// Increase target bitrate, either additively or multiplicatively
    Increase(IncreaseType),
}

struct Consumer {
    pipeline: gst::Pipeline,
    webrtcbin: gst::Element,
    webrtc_pads: HashMap<u32, WebRTCPad>,
    peer_id: String,
    encoders: Vec<VideoEncoder>,
    /// None if congestion control was disabled
    congestion_controller: Option<CongestionController>,
    sdp: Option<gst_sdp::SDPMessage>,
    stats: gst::Structure,

    max_bitrate: u32,
}

#[derive(PartialEq)]
enum SignallerState {
    Started,
    Stopped,
}

/* Our internal state */
struct State {
    signaller: Box<dyn super::SignallableObject>,
    signaller_state: SignallerState,
    consumers: HashMap<String, Consumer>,
    codecs: BTreeMap<i32, Codec>,
    /// Used to abort codec discovery
    codecs_abort_handle: Option<futures::future::AbortHandle>,
    /// Used to wait for the discovery task to fully stop
    codecs_done_receiver: Option<futures::channel::oneshot::Receiver<()>>,
    /// Used to determine whether we can start the signaller when going to Playing,
    /// or whether we should wait
    codec_discovery_done: bool,
    audio_serial: u32,
    video_serial: u32,
    streams: HashMap<String, InputStream>,
}

/// Simple utility for tearing down a pipeline cleanly
struct PipelineWrapper(gst::Pipeline);

/// Our instance structure
#[derive(Default)]
pub struct WebRTCSink {
    state: Mutex<State>,
    settings: Mutex<Settings>,
}

impl Default for Settings {
    fn default() -> Self {
        Self {
            video_caps: ["video/x-vp8", "video/x-h264", "video/x-vp9", "video/x-h265"]
                .iter()
                .map(|s| gst::Structure::new_empty(s))
                .collect::<gst::Caps>(),
            audio_caps: ["audio/x-opus"]
                .iter()
                .map(|s| gst::Structure::new_empty(s))
                .collect::<gst::Caps>(),
            cc_heuristic: WebRTCSinkCongestionControl::Homegrown,
            stun_server: DEFAULT_STUN_SERVER.map(String::from),
            turn_server: None,
            min_bitrate: DEFAULT_MIN_BITRATE,
            max_bitrate: DEFAULT_MAX_BITRATE,
            do_fec: DEFAULT_DO_FEC,
            do_retransmission: DEFAULT_DO_RETRANSMISSION,
        }
    }
}

impl Default for State {
    fn default() -> Self {
        let signaller = Signaller::default();

        Self {
            signaller: Box::new(signaller),
            signaller_state: SignallerState::Stopped,
            consumers: HashMap::new(),
            codecs: BTreeMap::new(),
            codecs_abort_handle: None,
            codecs_done_receiver: None,
            codec_discovery_done: false,
            audio_serial: 0,
            video_serial: 0,
            streams: HashMap::new(),
        }
    }
}

/// Bit of an awkward function, but the goal here is to keep
/// most of the encoding code for consumers in line with
/// the codec discovery code, and this gets the job done.
fn setup_encoding(
    pipeline: &gst::Pipeline,
    src: &gst::Element,
    codec: &Codec,
    ssrc: Option<u32>,
    twcc: bool,
) -> Result<(gst::Element, gst::Element, gst::Element), Error> {
    let conv = match codec.is_video {
        true => gst::parse_bin_from_description(
            "videoconvert ! videoscale ! videorate drop-only=true",
            true,
        )?
        .upcast(),
        false => gst::parse_bin_from_description("audioresample ! audioconvert", true)?.upcast(),
    };

    let conv_filter = make_element("capsfilter", None)?;

    let enc = codec
        .encoder
        .create(None)
        .with_context(|| format!("Creating encoder {}", codec.encoder.name()))?;
    let pay = codec
        .payloader
        .create(None)
        .with_context(|| format!("Creating payloader {}", codec.payloader.name()))?;
    let parse_filter = make_element("capsfilter", None)?;

    pay.set_property("pt", codec.payload as u32);

    if let Some(ssrc) = ssrc {
        pay.set_property("ssrc", ssrc);
    }

    pipeline
        .add_many(&[&conv, &conv_filter, &enc, &parse_filter, &pay])
        .unwrap();
    gst::Element::link_many(&[src, &conv, &conv_filter, &enc])
        .with_context(|| "Linking encoding elements")?;

    let codec_name = codec.caps.structure(0).unwrap().name();

    if let Some(parser) = if codec_name == "video/x-h264" {
        Some(make_element("h264parse", None)?)
    } else if codec_name == "video/x-h265" {
        Some(make_element("h265parse", None)?)
    } else {
        None
    } {
        pipeline.add(&parser).unwrap();
        gst::Element::link_many(&[&enc, &parser, &parse_filter])
            .with_context(|| "Linking encoding elements")?;
    } else {
        gst::Element::link_many(&[&enc, &parse_filter])
            .with_context(|| "Linking encoding elements")?;
    }

    // Quirk: nvh264enc can perform conversion from RGB formats, but
    // doesn't advertise / negotiate colorimetry correctly, leading
    // to incorrect color display in Chrome (but interestingly not in
    // Firefox). In any case, restrict to exclude RGB formats altogether,
    // and let videoconvert do the conversion properly if needed.
    let conv_caps = if codec.encoder.name() == "nvh264enc" {
        gst::Caps::builder("video/x-raw")
            .field("format", &gst::List::new(&[&"NV12", &"YV12", &"I420"]))
            .field("pixel-aspect-ratio", gst::Fraction::new(1, 1))
            .build()
    } else if codec.is_video {
        gst::Caps::builder("video/x-raw")
            .field("pixel-aspect-ratio", gst::Fraction::new(1, 1))
            .build()
    } else {
        gst::Caps::builder("audio/x-raw").build()
    };

    match codec.encoder.name().as_str() {
        "vp8enc" | "vp9enc" => {
            enc.set_property("deadline", 1i64);
            enc.set_property("threads", 12i32);
            enc.set_property("target-bitrate", 2560000i32);
            enc.set_property("cpu-used", -16i32);
            enc.set_property("keyframe-max-dist", 2000i32);
            enc.set_property_from_str("keyframe-mode", "disabled");
            enc.set_property_from_str("end-usage", "cbr");
            enc.set_property("buffer-initial-size", 100i32);
            enc.set_property("buffer-optimal-size", 120i32);
            enc.set_property("buffer-size", 150i32);
            enc.set_property("resize-allowed", true);
            enc.set_property("max-intra-bitrate", 250i32);
            enc.set_property_from_str("error-resilient", "default");
            pay.set_property_from_str("picture-id-mode", "15-bit");
        }
        "x264enc" => {
            enc.set_property("bitrate", 25608u32);
            enc.set_property_from_str("tune", "zerolatency");
            enc.set_property_from_str("speed-preset", "ultrafast");
            enc.set_property("threads", 12u32);
            enc.set_property("key-int-max", 2560u32);
            enc.set_property("b-adapt", false);
            enc.set_property("vbv-buf-capacity", 120u32);
        }
        "nvh264enc" => {
            enc.set_property("bitrate", 2048u32);
            enc.set_property("gop-size", 2560i32);
            enc.set_property_from_str("rc-mode", "cbr-ld-hq");
            enc.set_property("zerolatency", true);
        }
        _ => (),
    }

    /* We only enforce TWCC in the offer caps, once a remote description
     * has been set it will get automatically negotiated. This is necessary
     * because the implementor in Firefox had apparently not understood the
     * concept of *transport-wide* congestion control, and firefox doesn't
     * provide feedback for audio packets.
     */
    if twcc {
        let twcc_extension = gst_rtp::RTPHeaderExtension::create_from_uri(RTP_TWCC_URI).unwrap();
        twcc_extension.set_id(1);
        pay.emit_by_name::<()>("add-extension", &[&twcc_extension]);
    }

    conv_filter.set_property("caps", conv_caps);

    let parse_caps = if codec_name == "video/x-h264" {
        gst::Caps::builder(codec_name)
            .field("stream-format", "avc")
            .field("profile", "constrained-baseline")
            .build()
    } else if codec_name == "video/x-h265" {
        gst::Caps::builder(codec_name)
            .field("stream-format", "hvc1")
            .build()
    } else {
        gst::Caps::new_any()
    };

    parse_filter.set_property("caps", parse_caps);

    gst::Element::link_many(&[&parse_filter, &pay]).with_context(|| "Linking encoding elements")?;

    Ok((enc, conv_filter, pay))
}

fn lookup_remote_inbound_rtp_stats(stats: &gst::StructureRef) -> Option<gst::Structure> {
    for (_, field_value) in stats {
        if let Ok(s) = field_value.get::<gst::Structure>() {
            if let Ok(type_) = s.get::<gst_webrtc::WebRTCStatsType>("type") {
                if type_ == gst_webrtc::WebRTCStatsType::RemoteInboundRtp {
                    return Some(s);
                }
            }
        }
    }

    None
}

fn lookup_transport_stats(stats: &gst::StructureRef) -> Option<gst::Structure> {
    for (_, field_value) in stats {
        if let Ok(s) = field_value.get::<gst::Structure>() {
            if let Ok(type_) = s.get::<gst_webrtc::WebRTCStatsType>("type") {
                if type_ == gst_webrtc::WebRTCStatsType::Transport && s.has_field("gst-twcc-stats")
                {
                    return Some(s);
                }
            }
        }
    }

    None
}

impl VideoEncoder {
    fn new(
        element: gst::Element,
        filter: gst::Element,
        video_info: gst_video::VideoInfo,
        peer_id: &str,
        codec_name: &str,
        transceiver: gst_webrtc::WebRTCRTPTransceiver,
    ) -> Self {
        let halved_framerate = video_info.fps().mul(gst::Fraction::new(1, 2));

        Self {
            factory_name: element.factory().unwrap().name().into(),
            codec_name: codec_name.to_string(),
            element,
            filter,
            halved_framerate,
            video_info,
            peer_id: peer_id.to_string(),
            mitigation_mode: WebRTCSinkMitigationMode::NONE,
            transceiver,
        }
    }

    fn bitrate(&self) -> i32 {
        match self.factory_name.as_str() {
            "vp8enc" | "vp9enc" => self.element.property::<i32>("target-bitrate"),
            "x264enc" | "nvh264enc" => (self.element.property::<u32>("bitrate") * 1000) as i32,
            _ => unreachable!(),
        }
    }

    fn scale_height_round_2(&self, height: i32) -> i32 {
        let ratio = gst_video::calculate_display_ratio(
            self.video_info.width(),
            self.video_info.height(),
            self.video_info.par(),
            gst::Fraction::new(1, 1),
        )
        .unwrap();

        let width = height.mul_div_ceil(ratio.numer(), ratio.denom()).unwrap();

        (width + 1) & !1
    }

    fn set_bitrate(&mut self, element: &super::WebRTCSink, bitrate: i32) {
        match self.factory_name.as_str() {
            "vp8enc" | "vp9enc" => self.element.set_property("target-bitrate", bitrate),
            "x264enc" | "nvh264enc" => self
                .element
                .set_property("bitrate", (bitrate / 1000) as u32),
            _ => unreachable!(),
        }

        let mut s = self
            .filter
            .property::<gst::Caps>("caps")
            .structure(0)
            .unwrap()
            .to_owned();

        // Hardcoded thresholds, may be tuned further in the future, and
        // adapted according to the codec in use
        if bitrate < 500000 {
            let height = 360i32.min(self.video_info.height() as i32);
            let width = self.scale_height_round_2(height);

            s.set("height", height);
            s.set("width", width);
            s.set("framerate", self.halved_framerate);

            self.mitigation_mode =
                WebRTCSinkMitigationMode::DOWNSAMPLED | WebRTCSinkMitigationMode::DOWNSCALED;
        } else if bitrate < 1000000 {
            let height = 360i32.min(self.video_info.height() as i32);
            let width = self.scale_height_round_2(height);

            s.set("height", height);
            s.set("width", width);
            s.remove_field("framerate");

            self.mitigation_mode = WebRTCSinkMitigationMode::DOWNSCALED;
        } else if bitrate < 2000000 {
            let height = 720i32.min(self.video_info.height() as i32);
            let width = self.scale_height_round_2(height);

            s.set("height", height);
            s.set("width", width);
            s.remove_field("framerate");

            self.mitigation_mode = WebRTCSinkMitigationMode::DOWNSCALED;
        } else {
            s.remove_field("height");
            s.remove_field("width");
            s.remove_field("framerate");

            self.mitigation_mode = WebRTCSinkMitigationMode::NONE;
        }

        let caps = gst::Caps::builder_full().structure(s).build();

        gst_log!(
            CAT,
            obj: element,
            "consumer {}: setting bitrate {} and caps {} on encoder {:?}",
            self.peer_id,
            bitrate,
            caps,
            self.element
        );

        self.filter.set_property("caps", caps);
    }

    fn gather_stats(&self) -> gst::Structure {
        gst::Structure::builder("application/x-webrtcsink-video-encoder-stats")
            .field("bitrate", self.bitrate())
            .field("mitigation-mode", self.mitigation_mode)
            .field("codec-name", self.codec_name.as_str())
            .field(
                "fec-percentage",
                self.transceiver.property::<u32>("fec-percentage"),
            )
            .build()
    }
}

impl CongestionController {
    fn new(peer_id: &str, min_bitrate: u32, max_bitrate: u32) -> Self {
        Self {
            target_bitrate: 0,
            bitrate_ema: None,
            bitrate_emvar: 0.,
            last_update_time: None,
            peer_id: peer_id.to_string(),
            min_bitrate,
            max_bitrate,
        }
    }

    fn update(
        &mut self,
        element: &super::WebRTCSink,
        twcc_stats: &gst::StructureRef,
        rtt: f64,
    ) -> CongestionControlOp {
        let target_bitrate = self.target_bitrate as f64;
        // Unwrap, all those fields must be there or there's been an API
        // break, which qualifies as programming error
        let bitrate_sent = twcc_stats.get::<u32>("bitrate-sent").unwrap();
        let bitrate_recv = twcc_stats.get::<u32>("bitrate-recv").unwrap();
        let delta_of_delta = twcc_stats.get::<i64>("avg-delta-of-delta").unwrap();
        let loss_percentage = twcc_stats.get::<f64>("packet-loss-pct").unwrap();

        let sent_minus_received = bitrate_sent.saturating_sub(bitrate_recv);

        let delay_factor = sent_minus_received as f64 / target_bitrate;
        let last_update_time = self.last_update_time.replace(std::time::Instant::now());

        gst_trace!(
            CAT,
            obj: element,
            "consumer {}: considering stats {}",
            self.peer_id,
            twcc_stats
        );

        if delay_factor > 0.1 {
            CongestionControlOp::Decrease(if delay_factor < 0.64 {
                gst_trace!(
                    CAT,
                    obj: element,
                    "consumer {}: low delay factor {}",
                    self.peer_id,
                    delay_factor,
                );
                0.96
            } else {
                gst_trace!(
                    CAT,
                    obj: element,
                    "consumer {}: High delay factor",
                    self.peer_id
                );
                delay_factor.sqrt().sqrt().clamp(0.8, 0.96)
            })
        } else if delta_of_delta > 1000000 {
            CongestionControlOp::Decrease(if loss_percentage < 10. {
                gst_trace!(
                    CAT,
                    obj: element,
                    "consumer {}: moderate loss high delta",
                    self.peer_id
                );
                0.97
            } else {
                gst_log!(
                    CAT,
                    obj: element,
                    "consumer: {}: high loss high delta",
                    self.peer_id
                );
                ((100. - loss_percentage) / 100.).clamp(0.7, 0.98)
            })
        } else if loss_percentage > 10. {
            CongestionControlOp::Decrease(
                ((100. - (0.5 * loss_percentage)) / 100.).clamp(0.7, 0.98),
            )
        } else if loss_percentage > 2. {
            gst_trace!(
                CAT,
                obj: element,
                "consumer {}: moderate loss",
                self.peer_id
            );
            CongestionControlOp::Hold
        } else {
            gst_trace!(
                CAT,
                obj: element,
                "consumer {}: no detected congestion",
                self.peer_id
            );
            CongestionControlOp::Increase(if let Some(ema) = self.bitrate_ema {
                let bitrate_stdev = self.bitrate_emvar.sqrt();

                gst_trace!(
                    CAT,
                    obj: element,
                    "consumer {}: Old bitrate: {}, ema: {}, stddev: {}",
                    self.peer_id,
                    target_bitrate,
                    ema,
                    bitrate_stdev,
                );

                // gcc section 5.5 advises 3 standard deviations, but experiments
                // have shown this to be too low, probably related to the rest of
                // homegrown algorithm not implementing gcc, revisit when implementing
                // the rest of the RFC
                if target_bitrate < ema - 7. * bitrate_stdev {
                    gst_trace!(
                        CAT,
                        obj: element,
                        "consumer {}: below last congestion window",
                        self.peer_id
                    );
                    /* Multiplicative increase */
                    IncreaseType::Multiplicative(1.03)
                } else if target_bitrate > ema + 7. * bitrate_stdev {
                    gst_trace!(
                        CAT,
                        obj: element,
                        "consumer {}: above last congestion window",
                        self.peer_id
                    );
                    /* We have gone past our last estimated max bandwidth
                     * network situation may have changed, go back to
                     * multiplicative increase
                     */
                    self.bitrate_ema.take();
                    IncreaseType::Multiplicative(1.03)
                } else {
                    let rtt_ms = rtt * 1000.;
                    let response_time_ms = 100. + rtt_ms;
                    let time_since_last_update_ms = match last_update_time {
                        None => 0.,
                        Some(instant) => {
                            (self.last_update_time.unwrap() - instant).as_millis() as f64
                        }
                    };
                    // gcc section 5.5 advises 0.95 as the smoothing factor, but that
                    // seems intuitively much too low, granting disproportionate importance
                    // to the last measurement. 0.5 seems plenty enough, I don't have maths
                    // to back that up though :)
                    let alpha = 0.5 * f64::min(time_since_last_update_ms / response_time_ms, 1.0);
                    let bits_per_frame = target_bitrate / 30.;
                    let packets_per_frame = f64::ceil(bits_per_frame / (1200. * 8.));
                    let avg_packet_size_bits = bits_per_frame / packets_per_frame;

                    gst_trace!(
                        CAT,
                        obj: element,
                        "consumer {}: still in last congestion window",
                        self.peer_id,
                    );

                    /* Additive increase */
                    IncreaseType::Additive(f64::max(1000., alpha * avg_packet_size_bits))
                }
            } else {
                /* Multiplicative increase */
                gst_trace!(
                    CAT,
                    obj: element,
                    "consumer {}: outside congestion window",
                    self.peer_id
                );
                IncreaseType::Multiplicative(1.03)
            })
        }
    }

    fn clamp_bitrate(&mut self, bitrate: i32, n_encoders: i32) {
        self.target_bitrate = bitrate.clamp(
            self.min_bitrate as i32 * n_encoders,
            self.max_bitrate as i32 * n_encoders,
        );
    }

    fn control(
        &mut self,
        element: &super::WebRTCSink,
        stats: &gst::StructureRef,
        encoders: &mut Vec<VideoEncoder>,
    ) {
        let n_encoders = encoders.len() as i32;

        let rtt = lookup_remote_inbound_rtp_stats(stats)
            .and_then(|s| s.get::<f64>("round-trip-time").ok())
            .unwrap_or(0.);

        if let Some(twcc_stats) = lookup_transport_stats(stats).and_then(|transport_stats| {
            transport_stats.get::<gst::Structure>("gst-twcc-stats").ok()
        }) {
            let control_op = self.update(element, &twcc_stats, rtt);

            gst_trace!(
                CAT,
                obj: element,
                "consumer {}: applying congestion control operation {:?}",
                self.peer_id,
                control_op
            );

            match control_op {
                CongestionControlOp::Hold => (),
                CongestionControlOp::Increase(IncreaseType::Additive(value)) => {
                    self.clamp_bitrate(self.target_bitrate + value as i32, n_encoders);
                }
                CongestionControlOp::Increase(IncreaseType::Multiplicative(factor)) => {
                    self.clamp_bitrate((self.target_bitrate as f64 * factor) as i32, n_encoders);
                }
                CongestionControlOp::Decrease(factor) => {
                    self.clamp_bitrate((self.target_bitrate as f64 * factor) as i32, n_encoders);

                    // Smoothing factor
                    let alpha = 0.75;
                    if let Some(ema) = self.bitrate_ema {
                        let sigma: f64 = (self.target_bitrate as f64) - ema;
                        self.bitrate_ema = Some(ema + (alpha * sigma));
                        self.bitrate_emvar =
                            (1. - alpha) * (self.bitrate_emvar + alpha * sigma.powi(2));
                    } else {
                        self.bitrate_ema = Some(self.target_bitrate as f64);
                        self.bitrate_emvar = 0.;
                    }
                }
            }

            let target_bitrate = self.target_bitrate / n_encoders;

            let fec_ratio = {
                if target_bitrate <= 2000000 || self.max_bitrate <= 2000000 {
                    0f64
                } else {
                    (target_bitrate as f64 - 2000000f64) / (self.max_bitrate as f64 - 2000000f64)
                }
            };

            let fec_percentage = (fec_ratio * 50f64) as u32;

            for encoder in encoders.iter_mut() {
                encoder.set_bitrate(element, target_bitrate);
                encoder
                    .transceiver
                    .set_property("fec-percentage", fec_percentage);
            }
        }
    }
}

impl State {
    fn finalize_consumer(&mut self, element: &super::WebRTCSink, consumer: Consumer, signal: bool) {
        consumer.pipeline.debug_to_dot_file_with_ts(
            gst::DebugGraphDetails::all(),
            format!("removing-peer-{}-", consumer.peer_id,),
        );

        for webrtc_pad in consumer.webrtc_pads.values() {
            if let Some(producer) = self
                .streams
                .get(&webrtc_pad.stream_name)
                .and_then(|stream| stream.producer.as_ref())
            {
                consumer.disconnect_input_stream(producer);
            }
        }

        consumer.pipeline.call_async(|pipeline| {
            let _ = pipeline.set_state(gst::State::Null);
        });

        if signal {
            self.signaller.consumer_removed(element, &consumer.peer_id);
        }
    }

    fn remove_consumer(&mut self, element: &super::WebRTCSink, peer_id: &str, signal: bool) {
        if let Some(consumer) = self.consumers.remove(peer_id) {
            self.finalize_consumer(element, consumer, signal);
        }
    }

    fn maybe_start_signaller(&mut self, element: &super::WebRTCSink) {
        if self.signaller_state == SignallerState::Stopped
            && element.current_state() == gst::State::Playing
            && self.codec_discovery_done
        {
            if let Err(err) = self.signaller.start(element) {
                gst_error!(CAT, obj: element, "error: {}", err);
                gst::element_error!(
                    element,
                    gst::StreamError::Failed,
                    ["Failed to start signaller {}", err]
                );
            } else {
                gst_info!(CAT, "Started signaller");
                self.signaller_state = SignallerState::Started;
            }
        }
    }

    fn maybe_stop_signaller(&mut self, element: &super::WebRTCSink) {
        if self.signaller_state == SignallerState::Started {
            self.signaller.stop(element);
            self.signaller_state = SignallerState::Stopped;
            gst_info!(CAT, "Stopped signaller");
        }
    }
}

impl Consumer {
    fn gather_stats(&self) -> gst::Structure {
        let mut ret = self.stats.to_owned();

        let encoder_stats: Vec<_> = self
            .encoders
            .iter()
            .map(VideoEncoder::gather_stats)
            .map(|s| s.to_send_value())
            .collect();

        let our_stats = gst::Structure::builder("application/x-webrtcsink-consumer-stats")
            .field("video-encoders", gst::Array::from(encoder_stats))
            .build();

        ret.set("consumer-stats", our_stats);

        ret
    }

    fn generate_ssrc(&self) -> u32 {
        loop {
            let ret = fastrand::u32(..);

            if !self.webrtc_pads.contains_key(&ret) {
                return ret;
            }
        }
    }

    /// Request a sink pad on our webrtcbin, and set its transceiver's codec_preferences
    fn request_webrtcbin_pad(
        &mut self,
        element: &super::WebRTCSink,
        settings: &Settings,
        stream: &InputStream,
    ) {
        let ssrc = self.generate_ssrc();
        let media_idx = self.webrtc_pads.len() as i32;

        let mut payloader_caps = stream.out_caps.as_ref().unwrap().to_owned();

        {
            let payloader_caps_mut = payloader_caps.make_mut();
            payloader_caps_mut.set_simple(&[("ssrc", &ssrc)]);
        }

        gst_info!(
            CAT,
            obj: element,
            "Requesting WebRTC pad for consumer {} with caps {}",
            self.peer_id,
            payloader_caps
        );

        let pad = self
            .webrtcbin
            .request_pad_simple(&format!("sink_{}", media_idx))
            .unwrap();

        let transceiver = pad.property::<gst_webrtc::WebRTCRTPTransceiver>("transceiver");

        transceiver.set_property(
            "direction",
            gst_webrtc::WebRTCRTPTransceiverDirection::Sendonly,
        );

        transceiver.set_property("codec-preferences", &payloader_caps);

        if stream.sink_pad.name().starts_with("video_") {
            if settings.do_fec {
                transceiver.set_property("fec-type", gst_webrtc::WebRTCFECType::UlpRed);
            }

            transceiver.set_property("do-nack", settings.do_retransmission);
        }

        self.webrtc_pads.insert(
            ssrc,
            WebRTCPad {
                pad,
                in_caps: stream.in_caps.as_ref().unwrap().clone(),
                media_idx: media_idx as u32,
                ssrc,
                stream_name: stream.sink_pad.name().to_string(),
                payload: None,
            },
        );
    }

    /// Called when we have received an answer, connects an InputStream
    /// to a given WebRTCPad
    fn connect_input_stream(
        &mut self,
        element: &super::WebRTCSink,
        producer: &StreamProducer,
        webrtc_pad: &WebRTCPad,
        codecs: &BTreeMap<i32, Codec>,
    ) -> Result<(), Error> {
        gst_info!(
            CAT,
            obj: element,
            "Connecting input stream {} for consumer {}",
            webrtc_pad.stream_name,
            self.peer_id
        );

        let payload = webrtc_pad.payload.unwrap();

        let codec = codecs
            .get(&payload)
            .ok_or_else(|| anyhow!("No codec for payload {}", payload))?;

        let appsrc = make_element("appsrc", None)?;
        self.pipeline.add(&appsrc).unwrap();

        let pay_filter = make_element("capsfilter", None)?;
        self.pipeline.add(&pay_filter).unwrap();

        let (enc, raw_filter, pay) =
            setup_encoding(&self.pipeline, &appsrc, codec, Some(webrtc_pad.ssrc), false)?;

        // At this point, the peer has provided its answer, and we want to
        // let the payloader / encoder perform negotiation according to that.
        //
        // This means we need to unset our codec preferences, as they would now
        // conflict with what the peer actually requested (see webrtcbin's
        // caps query implementation), and instead install a capsfilter downstream
        // of the payloader with caps constructed from the relevant SDP media.
        let transceiver = webrtc_pad
            .pad
            .property::<gst_webrtc::WebRTCRTPTransceiver>("transceiver");
        transceiver.set_property("codec-preferences", None::<gst::Caps>);

        let mut global_caps = gst::Caps::new_simple("application/x-unknown", &[]);

        let sdp = self.sdp.as_ref().unwrap();
        let sdp_media = sdp.media(webrtc_pad.media_idx).unwrap();

        sdp.attributes_to_caps(global_caps.get_mut().unwrap())
            .unwrap();
        sdp_media
            .attributes_to_caps(global_caps.get_mut().unwrap())
            .unwrap();

        let caps = sdp_media
            .caps_from_media(payload)
            .unwrap()
            .intersect(&global_caps);
        let s = caps.structure(0).unwrap();
        let mut filtered_s = gst::Structure::new_empty("application/x-rtp");

        filtered_s.extend(s.iter().filter_map(|(key, value)| {
            if key.starts_with("a-") {
                None
            } else {
                Some((key, value.to_owned()))
            }
        }));
        filtered_s.set("ssrc", webrtc_pad.ssrc);

        let caps = gst::Caps::builder_full().structure(filtered_s).build();

        pay_filter.set_property("caps", caps);

        if codec.is_video {
            let video_info = gst_video::VideoInfo::from_caps(&webrtc_pad.in_caps)?;
            let mut enc = VideoEncoder::new(
                enc,
                raw_filter,
                video_info,
                &self.peer_id,
                codec.caps.structure(0).unwrap().name(),
                transceiver,
            );

            if let Some(congestion_controller) = self.congestion_controller.as_mut() {
                congestion_controller.target_bitrate += enc.bitrate();
                enc.transceiver.set_property("fec-percentage", 0u32);
            } else {
                /* If congestion control is disabled, we simply use the highest
                 * known "safe" value for the bitrate. */
                enc.set_bitrate(element, self.max_bitrate as i32);
                enc.transceiver.set_property("fec-percentage", 50u32);
            }

            self.encoders.push(enc);
        }

        let appsrc = appsrc.downcast::<gst_app::AppSrc>().unwrap();

        appsrc.set_format(gst::Format::Time);
        appsrc.set_is_live(true);
        appsrc.set_handle_segment_change(true);

        self.pipeline
            .sync_children_states()
            .with_context(|| format!("Connecting input stream for {}", self.peer_id))?;

        pay.link(&pay_filter)?;

        let srcpad = pay_filter.static_pad("src").unwrap();

        srcpad
            .link(&webrtc_pad.pad)
            .with_context(|| format!("Connecting input stream for {}", self.peer_id))?;

        producer.add_consumer(&appsrc, &self.peer_id);

        Ok(())
    }

    /// Called when tearing down the consumer
    fn disconnect_input_stream(&self, producer: &StreamProducer) {
        producer.remove_consumer(&self.peer_id);
    }
}

impl Drop for PipelineWrapper {
    fn drop(&mut self) {
        let _ = self.0.set_state(gst::State::Null);
    }
}

impl InputStream {
    /// Called when transitioning state up to Paused
    fn prepare(&mut self, element: &super::WebRTCSink) -> Result<(), Error> {
        let clocksync = make_element("clocksync", None)?;
        let appsink = make_element("appsink", None)?
            .downcast::<gst_app::AppSink>()
            .unwrap();

        element.add(&clocksync).unwrap();
        element.add(&appsink).unwrap();

        clocksync
            .link(&appsink)
            .with_context(|| format!("Linking input stream {}", self.sink_pad.name()))?;

        element
            .sync_children_states()
            .with_context(|| format!("Linking input stream {}", self.sink_pad.name()))?;

        self.sink_pad
            .set_target(Some(&clocksync.static_pad("sink").unwrap()))
            .unwrap();

        let producer = StreamProducer::from(&appsink);
        producer.forward();

        self.producer = Some(producer);

        Ok(())
    }

    /// Called when transitioning state back down to Ready
    fn unprepare(&mut self, element: &super::WebRTCSink) {
        self.sink_pad.set_target(None::<&gst::Pad>).unwrap();

        if let Some(clocksync) = self.clocksync.take() {
            element.remove(&clocksync).unwrap();
            clocksync.set_state(gst::State::Null).unwrap();
        }

        if let Some(producer) = self.producer.take() {
            let appsink = producer.appsink().upcast_ref::<gst::Element>();
            element.remove(appsink).unwrap();
            appsink.set_state(gst::State::Null).unwrap();
        }
    }
}

impl WebRTCSink {
    /// Build an ordered map of Codecs, given user-provided audio / video caps */
    fn lookup_codecs(&self) -> BTreeMap<i32, Codec> {
        /* First gather all encoder and payloader factories */
        let encoders = gst::ElementFactory::factories_with_type(
            gst::ElementFactoryType::ENCODER,
            gst::Rank::Marginal,
        );

        let payloaders = gst::ElementFactory::factories_with_type(
            gst::ElementFactoryType::PAYLOADER,
            gst::Rank::Marginal,
        );

        /* Now iterate user-provided codec preferences and determine
         * whether we can fulfill these preferences */
        let settings = self.settings.lock().unwrap();
        let mut payload = 96..128;

        settings
            .video_caps
            .iter()
            .map(|s| (true, s))
            .chain(settings.audio_caps.iter().map(|s| (false, s)))
            .filter_map(move |(is_video, s)| {
                let caps = gst::Caps::builder_full().structure(s.to_owned()).build();

                Option::zip(
                    encoders
                        .iter()
                        .find(|factory| factory.can_src_any_caps(&caps)),
                    payloaders
                        .iter()
                        .find(|factory| factory.can_sink_any_caps(&caps)),
                )
                .and_then(|(encoder, payloader)| {
                    /* Assign a payload type to the codec */
                    if let Some(pt) = payload.next() {
                        Some(Codec {
                            is_video,
                            encoder: encoder.clone(),
                            payloader: payloader.clone(),
                            caps,
                            payload: pt,
                        })
                    } else {
                        gst_warning!(CAT, obj: &self.instance(),
                                "Too many formats for available payload type range, ignoring {}",
                                s);
                        None
                    }
                })
            })
            .map(|codec| (codec.payload, codec))
            .collect()
    }

    /// Prepare for accepting consumers, by setting
    /// up StreamProducers for each of our sink pads
    fn prepare(&self, element: &super::WebRTCSink) -> Result<(), Error> {
        gst_debug!(CAT, obj: element, "preparing");

        self.state
            .lock()
            .unwrap()
            .streams
            .iter_mut()
            .try_for_each(|(_, stream)| stream.prepare(element))?;

        Ok(())
    }

    /// Unprepare by stopping consumers, then the signaller object.
    /// Might abort codec discovery
    fn unprepare(&self, element: &super::WebRTCSink) -> Result<(), Error> {
        gst_info!(CAT, obj: element, "unpreparing");

        let mut state = self.state.lock().unwrap();

        let consumer_ids: Vec<_> = state.consumers.keys().map(|k| k.to_owned()).collect();

        for id in consumer_ids {
            state.remove_consumer(element, &id, true);
        }

        state
            .streams
            .iter_mut()
            .for_each(|(_, stream)| stream.unprepare(element));

        if let Some(handle) = state.codecs_abort_handle.take() {
            handle.abort();
        }

        if let Some(receiver) = state.codecs_done_receiver.take() {
            task::block_on(async {
                let _ = receiver.await;
            });
        }

        state.maybe_stop_signaller(element);

        state.codec_discovery_done = false;
        state.codecs = BTreeMap::new();

        Ok(())
    }

    /// When using a custom signaller
    pub fn set_signaller(&self, signaller: Box<dyn super::SignallableObject>) -> Result<(), Error> {
        let mut state = self.state.lock().unwrap();

        state.signaller = signaller;

        Ok(())
    }

    /// Called by the signaller when it has encountered an error
    pub fn handle_signalling_error(&self, element: &super::WebRTCSink, error: anyhow::Error) {
        gst_error!(CAT, obj: element, "Signalling error: {:?}", error);

        gst::element_error!(
            element,
            gst::StreamError::Failed,
            ["Signalling error: {:?}", error]
        );
    }

    fn on_offer_created(
        &self,
        element: &super::WebRTCSink,
        offer: gst_webrtc::WebRTCSessionDescription,
        peer_id: String,
    ) {
        let mut state = self.state.lock().unwrap();

        if let Some(consumer) = state.consumers.get(&peer_id) {
            consumer
                .webrtcbin
                .emit_by_name::<()>("set-local-description", &[&offer, &None::<gst::Promise>]);

            if let Err(err) = state.signaller.handle_sdp(element, &peer_id, &offer) {
                gst_warning!(
                    CAT,
                    "Failed to handle SDP for consumer {}: {}",
                    peer_id,
                    err
                );

                state.remove_consumer(element, &peer_id, true);
            }
        }
    }

    fn on_negotiation_needed(&self, element: &super::WebRTCSink, peer_id: String) {
        let state = self.state.lock().unwrap();

        gst_debug!(
            CAT,
            obj: element,
            "On negotiation needed for peer {}",
            peer_id
        );

        if let Some(consumer) = state.consumers.get(&peer_id) {
            let element = element.downgrade();
            gst_debug!(CAT, "Creating offer for peer {}", peer_id);
            let promise = gst::Promise::with_change_func(move |reply| {
                gst_debug!(CAT, "Created offer for peer {}", peer_id);

                if let Some(element) = element.upgrade() {
                    let this = Self::from_instance(&element);
                    let reply = match reply {
                        Ok(Some(reply)) => reply,
                        Ok(None) => {
                            gst_warning!(
                                CAT,
                                obj: &element,
                                "Promise returned without a reply for {}",
                                peer_id
                            );
                            let _ = this.remove_consumer(&element, &peer_id, true);
                            return;
                        }
                        Err(err) => {
                            gst_warning!(
                                CAT,
                                obj: &element,
                                "Promise returned with an error for {}: {:?}",
                                peer_id,
                                err
                            );
                            let _ = this.remove_consumer(&element, &peer_id, true);
                            return;
                        }
                    };

                    if let Ok(offer) = reply
                        .value("offer")
                        .map(|offer| offer.get::<gst_webrtc::WebRTCSessionDescription>().unwrap())
                    {
                        this.on_offer_created(&element, offer, peer_id);
                    } else {
                        gst_warning!(
                            CAT,
                            "Reply without an offer for consumer {}: {:?}",
                            peer_id,
                            reply
                        );
                        let _ = this.remove_consumer(&element, &peer_id, true);
                    }
                }
            });

            consumer
                .webrtcbin
                .emit_by_name::<()>("create-offer", &[&None::<gst::Structure>, &promise]);
        } else {
            gst_debug!(
                CAT,
                obj: element,
                "consumer for peer {} no longer exists",
                peer_id
            );
        }
    }

    fn on_ice_candidate(
        &self,
        element: &super::WebRTCSink,
        peer_id: String,
        sdp_mline_index: u32,
        candidate: String,
    ) {
        let mut state = self.state.lock().unwrap();
        if let Err(err) =
            state
                .signaller
                .handle_ice(element, &peer_id, &candidate, Some(sdp_mline_index), None)
        {
            gst_warning!(
                CAT,
                "Failed to handle ICE for consumer {}: {}",
                peer_id,
                err
            );

            state.remove_consumer(element, &peer_id, true);
        }
    }

    /// Called by the signaller to add a new consumer
    pub fn add_consumer(
        &self,
        element: &super::WebRTCSink,
        peer_id: &str,
    ) -> Result<(), WebRTCSinkError> {
        let settings = self.settings.lock().unwrap();
        let mut state = self.state.lock().unwrap();

        if state.consumers.contains_key(peer_id) {
            return Err(WebRTCSinkError::DuplicateConsumerId(peer_id.to_string()));
        }

        gst_info!(CAT, obj: element, "Adding consumer {}", peer_id);

        let pipeline = gst::Pipeline::new(Some(&format!("consumer-pipeline-{}", peer_id)));

        let webrtcbin = make_element("webrtcbin", None).map_err(|err| {
            WebRTCSinkError::ConsumerPipelineError {
                peer_id: peer_id.to_string(),
                details: err.to_string(),
            }
        })?;

        webrtcbin.set_property_from_str("bundle-policy", "max-bundle");

        if let Some(stun_server) = settings.stun_server.as_ref() {
            webrtcbin.set_property("stun-server", stun_server);
        }

        if let Some(turn_server) = settings.turn_server.as_ref() {
            webrtcbin.set_property("turn-server", turn_server);
        }

        pipeline.add(&webrtcbin).unwrap();

        let element_clone = element.downgrade();
        let peer_id_clone = peer_id.to_owned();
        webrtcbin.connect("on-negotiation-needed", false, move |_| {
            if let Some(element) = element_clone.upgrade() {
                let this = Self::from_instance(&element);
                this.on_negotiation_needed(&element, peer_id_clone.to_string());
            }

            None
        });

        let element_clone = element.downgrade();
        let peer_id_clone = peer_id.to_owned();
        webrtcbin.connect("on-ice-candidate", false, move |values| {
            if let Some(element) = element_clone.upgrade() {
                let this = Self::from_instance(&element);
                let sdp_mline_index = values[1].get::<u32>().expect("Invalid argument");
                let candidate = values[2].get::<String>().expect("Invalid argument");
                this.on_ice_candidate(
                    &element,
                    peer_id_clone.to_string(),
                    sdp_mline_index,
                    candidate,
                );
            }
            None
        });

        let element_clone = element.downgrade();
        let peer_id_clone = peer_id.to_owned();
        webrtcbin.connect_notify(Some("connection-state"), move |webrtcbin, _pspec| {
            if let Some(element) = element_clone.upgrade() {
                let state =
                    webrtcbin.property::<gst_webrtc::WebRTCPeerConnectionState>("connection-state");

                match state {
                    gst_webrtc::WebRTCPeerConnectionState::Failed => {
                        let this = Self::from_instance(&element);
                        gst_warning!(
                            CAT,
                            obj: &element,
                            "Connection state for consumer {} failed",
                            peer_id_clone
                        );
                        let _ = this.remove_consumer(&element, &peer_id_clone, true);
                    }
                    _ => {
                        gst_log!(
                            CAT,
                            obj: &element,
                            "Connection state for consumer {} changed: {:?}",
                            peer_id_clone,
                            state
                        );
                    }
                }
            }
        });

        let element_clone = element.downgrade();
        let peer_id_clone = peer_id.to_owned();
        webrtcbin.connect_notify(Some("ice-connection-state"), move |webrtcbin, _pspec| {
            if let Some(element) = element_clone.upgrade() {
                let state = webrtcbin
                    .property::<gst_webrtc::WebRTCICEConnectionState>("ice-connection-state");
                let this = Self::from_instance(&element);

                match state {
                    gst_webrtc::WebRTCICEConnectionState::Failed => {
                        gst_warning!(
                            CAT,
                            obj: &element,
                            "Ice connection state for consumer {} failed",
                            peer_id_clone
                        );
                        let _ = this.remove_consumer(&element, &peer_id_clone, true);
                    }
                    _ => {
                        gst_log!(
                            CAT,
                            obj: &element,
                            "Ice connection state for consumer {} changed: {:?}",
                            peer_id_clone,
                            state
                        );
                    }
                }

                if state == gst_webrtc::WebRTCICEConnectionState::Completed {
                    let state = this.state.lock().unwrap();

                    if let Some(consumer) = state.consumers.get(&peer_id_clone) {
                        for webrtc_pad in consumer.webrtc_pads.values() {
                            if let Some(srcpad) = webrtc_pad.pad.peer() {
                                srcpad.send_event(
                                    gst_video::UpstreamForceKeyUnitEvent::builder()
                                        .all_headers(true)
                                        .build(),
                                );
                            }
                        }
                    }
                }
            }
        });

        let element_clone = element.downgrade();
        let peer_id_clone = peer_id.to_owned();
        webrtcbin.connect_notify(Some("ice-gathering-state"), move |webrtcbin, _pspec| {
            let state =
                webrtcbin.property::<gst_webrtc::WebRTCICEGatheringState>("ice-gathering-state");

            if let Some(element) = element_clone.upgrade() {
                gst_log!(
                    CAT,
                    obj: &element,
                    "Ice gathering state for consumer {} changed: {:?}",
                    peer_id_clone,
                    state
                );
            }
        });

        let mut consumer = Consumer {
            pipeline: pipeline.clone(),
            webrtcbin: webrtcbin.clone(),
            webrtc_pads: HashMap::new(),
            peer_id: peer_id.to_string(),
            congestion_controller: match settings.cc_heuristic {
                WebRTCSinkCongestionControl::Disabled => None,
                WebRTCSinkCongestionControl::Homegrown => Some(CongestionController::new(
                    peer_id,
                    settings.min_bitrate,
                    settings.max_bitrate,
                )),
            },
            encoders: Vec::new(),
            sdp: None,
            stats: gst::Structure::new_empty("application/x-webrtc-stats"),
            max_bitrate: settings.max_bitrate,
        };

        state
            .streams
            .iter()
            .for_each(|(_, stream)| consumer.request_webrtcbin_pad(element, &settings, stream));

        let clock = element.clock();

        pipeline.set_clock(clock.as_ref()).unwrap();
        pipeline.set_start_time(gst::ClockTime::NONE);
        pipeline.set_base_time(element.base_time().unwrap());

        let mut bus_stream = pipeline.bus().unwrap().stream();
        let element_clone = element.downgrade();
        let pipeline_clone = pipeline.downgrade();
        let peer_id_clone = peer_id.to_owned();

        task::spawn(async move {
            while let Some(msg) = bus_stream.next().await {
                if let Some(element) = element_clone.upgrade() {
                    let this = Self::from_instance(&element);
                    match msg.view() {
                        gst::MessageView::Error(err) => {
                            gst_error!(
                                CAT,
                                "Consumer {} error: {}, details: {:?}",
                                peer_id_clone,
                                err.error(),
                                err.debug()
                            );
                            let _ = this.remove_consumer(&element, &peer_id_clone, true);
                        }
                        gst::MessageView::StateChanged(state_changed) => {
                            if let Some(pipeline) = pipeline_clone.upgrade() {
                                if Some(pipeline.clone().upcast()) == state_changed.src() {
                                    pipeline.debug_to_dot_file_with_ts(
                                        gst::DebugGraphDetails::all(),
                                        format!(
                                            "webrtcsink-peer-{}-{:?}-to-{:?}",
                                            peer_id_clone,
                                            state_changed.old(),
                                            state_changed.current()
                                        ),
                                    );
                                }
                            }
                        }
                        gst::MessageView::Eos(..) => {
                            gst_error!(
                                CAT,
                                "Unexpected end of stream for consumer {}",
                                peer_id_clone
                            );
                            let _ = this.remove_consumer(&element, &peer_id_clone, true);
                        }
                        _ => (),
                    }
                }
            }
        });

        pipeline.set_state(gst::State::Ready).map_err(|err| {
            WebRTCSinkError::ConsumerPipelineError {
                peer_id: peer_id.to_string(),
                details: err.to_string(),
            }
        })?;

        element.emit_by_name::<()>("new-webrtcbin", &[&peer_id, &webrtcbin]);

        pipeline.set_state(gst::State::Playing).map_err(|err| {
            WebRTCSinkError::ConsumerPipelineError {
                peer_id: peer_id.to_string(),
                details: err.to_string(),
            }
        })?;

        state.consumers.insert(peer_id.to_string(), consumer);

        Ok(())
    }

    /// Called by the signaller to remove a consumer
    pub fn remove_consumer(
        &self,
        element: &super::WebRTCSink,
        peer_id: &str,
        signal: bool,
    ) -> Result<(), WebRTCSinkError> {
        let mut state = self.state.lock().unwrap();

        if !state.consumers.contains_key(peer_id) {
            return Err(WebRTCSinkError::NoConsumerWithId(peer_id.to_string()));
        }

        state.remove_consumer(element, peer_id, signal);

        Ok(())
    }

    fn process_webrtcbin_stats(
        &self,
        element: &super::WebRTCSink,
        peer_id: &str,
        stats: &gst::StructureRef,
    ) {
        let mut state = self.state.lock().unwrap();

        if let Some(consumer) = state.consumers.get_mut(peer_id) {
            if let Some(congestion_controller) = consumer.congestion_controller.as_mut() {
                congestion_controller.control(element, stats, &mut consumer.encoders);
            }
            consumer.stats = stats.to_owned();
        }
    }

    fn on_remote_description_set(&self, element: &super::WebRTCSink, peer_id: String) {
        let mut state = self.state.lock().unwrap();
        let mut remove = false;

        if let Some(mut consumer) = state.consumers.remove(&peer_id) {
            for webrtc_pad in consumer.webrtc_pads.clone().values() {
                if let Some(producer) = state
                    .streams
                    .get(&webrtc_pad.stream_name)
                    .and_then(|stream| stream.producer.as_ref())
                {
                    if let Err(err) =
                        consumer.connect_input_stream(element, producer, webrtc_pad, &state.codecs)
                    {
                        gst_error!(
                            CAT,
                            obj: element,
                            "Failed to connect input stream {} for consumer {}: {}",
                            webrtc_pad.stream_name,
                            peer_id,
                            err
                        );
                        remove = true;
                        break;
                    }
                } else {
                    gst_error!(
                        CAT,
                        obj: element,
                        "No producer to connect consumer {} to",
                        peer_id,
                    );
                    remove = true;
                    break;
                }
            }

            consumer.pipeline.debug_to_dot_file_with_ts(
                gst::DebugGraphDetails::all(),
                format!("webrtcsink-peer-{}-remote-description-set", peer_id,),
            );

            let element_clone = element.downgrade();
            let webrtcbin = consumer.webrtcbin.downgrade();
            let peer_id_clone = peer_id.clone();

            task::spawn(async move {
                let mut interval =
                    async_std::stream::interval(std::time::Duration::from_millis(100));

                while interval.next().await.is_some() {
                    let element_clone = element_clone.clone();
                    let peer_id_clone = peer_id_clone.clone();
                    if let Some(webrtcbin) = webrtcbin.upgrade() {
                        let promise = gst::Promise::with_change_func(move |reply| {
                            if let Some(element) = element_clone.upgrade() {
                                let this = Self::from_instance(&element);

                                if let Ok(Some(stats)) = reply {
                                    this.process_webrtcbin_stats(&element, &peer_id_clone, stats);
                                }
                            }
                        });

                        webrtcbin.emit_by_name::<()>("get-stats", &[&None::<gst::Pad>, &promise]);
                    } else {
                        break;
                    }
                }
            });

            if remove {
                state.finalize_consumer(element, consumer, true);
            } else {
                state.consumers.insert(consumer.peer_id.clone(), consumer);
            }
        }
    }

    /// Called by the signaller with an ice candidate
    pub fn handle_ice(
        &self,
        _element: &super::WebRTCSink,
        peer_id: &str,
        sdp_mline_index: Option<u32>,
        _sdp_mid: Option<String>,
        candidate: &str,
    ) -> Result<(), WebRTCSinkError> {
        let state = self.state.lock().unwrap();

        let sdp_mline_index = sdp_mline_index.ok_or(WebRTCSinkError::MandatorySdpMlineIndex)?;

        if let Some(consumer) = state.consumers.get(peer_id) {
            gst_trace!(CAT, "adding ice candidate for peer {}", peer_id);
            consumer
                .webrtcbin
                .emit_by_name::<()>("add-ice-candidate", &[&sdp_mline_index, &candidate]);
            Ok(())
        } else {
            Err(WebRTCSinkError::NoConsumerWithId(peer_id.to_string()))
        }
    }

    /// Called by the signaller with an answer to our offer
    pub fn handle_sdp(
        &self,
        element: &super::WebRTCSink,
        peer_id: &str,
        desc: &gst_webrtc::WebRTCSessionDescription,
    ) -> Result<(), WebRTCSinkError> {
        let mut state = self.state.lock().unwrap();

        if let Some(consumer) = state.consumers.get_mut(peer_id) {
            let sdp = desc.sdp();

            consumer.sdp = Some(sdp.to_owned());

            for webrtc_pad in consumer.webrtc_pads.values_mut() {
                let media_idx = webrtc_pad.media_idx;
                /* TODO: support partial answer, webrtcbin doesn't seem
                 * very well equipped to deal with this at the moment */
                if let Some(media) = sdp.media(media_idx) {
                    if media.attribute_val("inactive").is_some() {
                        gst_warning!(CAT, "consumer {} refused media {}", peer_id, media_idx);
                        state.remove_consumer(element, peer_id, true);

                        return Err(WebRTCSinkError::ConsumerRefusedMedia {
                            peer_id: peer_id.to_string(),
                            media_idx,
                        });
                    }
                }

                if let Some(payload) = sdp
                    .media(webrtc_pad.media_idx)
                    .and_then(|media| media.format(0))
                    .and_then(|format| format.parse::<i32>().ok())
                {
                    webrtc_pad.payload = Some(payload);
                } else {
                    gst_warning!(
                        CAT,
                        "consumer {} did not provide valid payload for media index {}",
                        peer_id,
                        media_idx
                    );

                    state.remove_consumer(element, peer_id, true);

                    return Err(WebRTCSinkError::ConsumerNoValidPayload {
                        peer_id: peer_id.to_string(),
                        media_idx,
                    });
                }
            }

            let element = element.downgrade();
            let peer_id = peer_id.to_string();

            let promise = gst::Promise::with_change_func(move |reply| {
                gst_debug!(CAT, "received reply {:?}", reply);
                if let Some(element) = element.upgrade() {
                    let this = Self::from_instance(&element);

                    this.on_remote_description_set(&element, peer_id);
                }
            });

            consumer
                .webrtcbin
                .emit_by_name::<()>("set-remote-description", &[desc, &promise]);

            Ok(())
        } else {
            Err(WebRTCSinkError::NoConsumerWithId(peer_id.to_string()))
        }
    }

    async fn run_discovery_pipeline(
        _element: &super::WebRTCSink,
        codec: &Codec,
        caps: &gst::Caps,
    ) -> Result<gst::Structure, Error> {
        let pipe = PipelineWrapper(gst::Pipeline::new(None));

        let src = match codec.is_video {
            true => make_element("videotestsrc", None)?,
            false => make_element("audiotestsrc", None)?,
        };
        let capsfilter = make_element("capsfilter", None)?;

        pipe.0.add_many(&[&src, &capsfilter]).unwrap();
        src.link(&capsfilter)
            .with_context(|| format!("Running discovery pipeline for caps {}", caps))?;

        let (_, _, pay) = setup_encoding(&pipe.0, &capsfilter, codec, None, true)?;

        let sink = make_element("fakesink", None)?;

        pipe.0.add(&sink).unwrap();

        pay.link(&sink)
            .with_context(|| format!("Running discovery pipeline for caps {}", caps))?;

        capsfilter.set_property("caps", caps);

        src.set_property("num-buffers", 1);

        let mut stream = pipe.0.bus().unwrap().stream();

        pipe.0
            .set_state(gst::State::Playing)
            .with_context(|| format!("Running discovery pipeline for caps {}", caps))?;

        while let Some(msg) = stream.next().await {
            match msg.view() {
                gst::MessageView::Error(err) => {
                    return Err(err.error().into());
                }
                gst::MessageView::Eos(_) => {
                    let caps = pay.static_pad("src").unwrap().current_caps().unwrap();

                    if let Some(s) = caps.structure(0) {
                        let mut s = s.to_owned();
                        s.remove_fields(&[
                            "timestamp-offset",
                            "seqnum-offset",
                            "ssrc",
                            "sprop-parameter-sets",
                            "a-framerate",
                        ]);
                        s.set("payload", codec.payload);
                        return Ok(s);
                    } else {
                        return Err(anyhow!("Discovered empty caps"));
                    }
                }
                _ => {
                    continue;
                }
            }
        }

        unreachable!()
    }

    async fn lookup_caps(
        element: &super::WebRTCSink,
        name: String,
        in_caps: gst::Caps,
        codecs: &BTreeMap<i32, Codec>,
    ) -> (String, gst::Caps) {
        let sink_caps = in_caps.as_ref().to_owned();

        let is_video = match sink_caps.structure(0).unwrap().name() {
            "video/x-raw" => true,
            "audio/x-raw" => false,
            _ => unreachable!(),
        };

        let mut payloader_caps = gst::Caps::new_empty();
        let payloader_caps_mut = payloader_caps.make_mut();

        let futs = codecs
            .iter()
            .filter(|(_, codec)| codec.is_video == is_video)
            .map(|(_, codec)| WebRTCSink::run_discovery_pipeline(element, codec, &sink_caps));

        for ret in futures::future::join_all(futs).await {
            match ret {
                Ok(s) => {
                    payloader_caps_mut.append_structure(s);
                }
                Err(err) => {
                    /* We don't consider this fatal, as long as we end up with one
                     * potential codec for each input stream
                     */
                    gst_warning!(
                        CAT,
                        obj: element,
                        "Codec discovery pipeline failed: {}",
                        err
                    );
                }
            }
        }

        (name, payloader_caps)
    }

    async fn lookup_streams_caps(&self, element: &super::WebRTCSink) -> Result<(), Error> {
        let codecs = self.lookup_codecs();
        let futs: Vec<_> = self
            .state
            .lock()
            .unwrap()
            .streams
            .iter()
            .map(|(name, stream)| {
                WebRTCSink::lookup_caps(
                    element,
                    name.to_owned(),
                    stream.in_caps.as_ref().unwrap().to_owned(),
                    &codecs,
                )
            })
            .collect();

        let caps: Vec<(String, gst::Caps)> = futures::future::join_all(futs).await;

        let mut state = self.state.lock().unwrap();

        for (name, caps) in caps {
            if caps.is_empty() {
                return Err(anyhow!("No caps found for stream {}", name));
            }

            if let Some(mut stream) = state.streams.get_mut(&name) {
                stream.out_caps = Some(caps);
            }
        }

        state.codecs = codecs;

        Ok(())
    }

    fn gather_stats(&self) -> gst::Structure {
        gst::Structure::from_iter(
            "application/x-webrtcsink-stats",
            self.state
                .lock()
                .unwrap()
                .consumers
                .iter()
                .map(|(name, consumer)| (name.as_str(), consumer.gather_stats().to_send_value())),
        )
    }

    fn sink_event(&self, pad: &gst::Pad, element: &super::WebRTCSink, event: gst::Event) -> bool {
        use gst::EventView;

        match event.view() {
            EventView::Caps(e) => {
                if let Some(caps) = pad.current_caps() {
                    if caps.is_strictly_equal(e.caps()) {
                        // Nothing changed
                        true
                    } else {
                        gst_error!(CAT, obj: pad, "Renegotiation is not supported");
                        false
                    }
                } else {
                    gst_info!(CAT, obj: pad, "Received caps event {:?}", e);

                    let mut all_pads_have_caps = true;

                    self.state
                        .lock()
                        .unwrap()
                        .streams
                        .iter_mut()
                        .for_each(|(_, mut stream)| {
                            if stream.sink_pad.upcast_ref::<gst::Pad>() == pad {
                                stream.in_caps = Some(e.caps().to_owned());
                            } else if stream.in_caps.is_none() {
                                all_pads_have_caps = false;
                            }
                        });

                    if all_pads_have_caps {
                        let element_clone = element.downgrade();
                        task::spawn(async move {
                            if let Some(element) = element_clone.upgrade() {
                                let this = Self::from_instance(&element);
                                let (fut, handle) =
                                    futures::future::abortable(this.lookup_streams_caps(&element));

                                let (codecs_done_sender, codecs_done_receiver) =
                                    futures::channel::oneshot::channel();

                                // Compiler isn't budged by dropping state before await,
                                // so let's make a new scope instead.
                                {
                                    let mut state = this.state.lock().unwrap();
                                    state.codecs_abort_handle = Some(handle);
                                    state.codecs_done_receiver = Some(codecs_done_receiver);
                                }

                                match fut.await {
                                    Ok(Err(err)) => {
                                        gst_error!(CAT, obj: &element, "error: {}", err);
                                        gst::element_error!(
                                            element,
                                            gst::StreamError::CodecNotFound,
                                            ["Failed to look up output caps: {}", err]
                                        );
                                    }
                                    Ok(Ok(_)) => {
                                        let mut state = this.state.lock().unwrap();
                                        state.codec_discovery_done = true;
                                        state.maybe_start_signaller(&element);
                                    }
                                    _ => (),
                                }

                                let _ = codecs_done_sender.send(());
                            }
                        });
                    }

                    pad.event_default(Some(element), event)
                }
            }
            _ => pad.event_default(Some(element), event),
        }
    }
}

#[glib::object_subclass]
impl ObjectSubclass for WebRTCSink {
    const NAME: &'static str = "RsWebRTCSink";
    type Type = super::WebRTCSink;
    type ParentType = gst::Bin;
    type Interfaces = (gst::ChildProxy,);
}

impl ObjectImpl for WebRTCSink {
    fn properties() -> &'static [glib::ParamSpec] {
        static PROPERTIES: Lazy<Vec<glib::ParamSpec>> = Lazy::new(|| {
            vec![
                glib::ParamSpecBoxed::new(
                    "video-caps",
                    "Video encoder caps",
                    "Governs what video codecs will be proposed",
                    gst::Caps::static_type(),
                    glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_READY,
                ),
                glib::ParamSpecBoxed::new(
                    "audio-caps",
                    "Audio encoder caps",
                    "Governs what audio codecs will be proposed",
                    gst::Caps::static_type(),
                    glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_READY,
                ),
                glib::ParamSpecString::new(
                    "stun-server",
                    "STUN Server",
                    "The STUN server of the form stun://hostname:port",
                    DEFAULT_STUN_SERVER,
                    glib::ParamFlags::READWRITE,
                ),
                glib::ParamSpecString::new(
                    "turn-server",
                    "TURN Server",
                    "The TURN server of the form turn(s)://username:password@host:port.",
                    None,
                    glib::ParamFlags::READWRITE,
                ),
                glib::ParamSpecEnum::new(
                    "congestion-control",
                    "Congestion control",
                    "Defines how congestion is controlled, if at all",
                    WebRTCSinkCongestionControl::static_type(),
                    DEFAULT_CONGESTION_CONTROL as i32,
                    glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_PLAYING,
                ),
                glib::ParamSpecUInt::new(
                    "min-bitrate",
                    "Minimal Bitrate",
                    "Minimal bitrate to use (in bit/sec) when computing it through the congestion control algorithm",
                    1,
                    u32::MAX as u32,
                    DEFAULT_MIN_BITRATE,
                    glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_READY,
                ),
                glib::ParamSpecUInt::new(
                    "max-bitrate",
                    "Minimal Bitrate",
                    "Minimal bitrate to use (in bit/sec) when computing it through the congestion control algorithm",
                    1,
                    u32::MAX as u32,
                    DEFAULT_MAX_BITRATE,
                    glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_READY,
                ),
                glib::ParamSpecBoxed::new(
                    "stats",
                    "Consumer statistics",
                    "Statistics for the current consumers",
                    gst::Structure::static_type(),
                    glib::ParamFlags::READABLE,
                ),
                glib::ParamSpecBoolean::new(
                    "do-fec",
                    "Do Forward Error Correction",
                    "Whether the element should negotiate and send FEC data",
                    DEFAULT_DO_FEC,
                    glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_READY
                ),
                glib::ParamSpecBoolean::new(
                    "do-retransmission",
                    "Do retransmission",
                    "Whether the element should offer to honor retransmission requests",
                    DEFAULT_DO_RETRANSMISSION,
                    glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_READY
                ),
            ]
        });

        PROPERTIES.as_ref()
    }

    fn set_property(
        &self,
        _obj: &Self::Type,
        _id: usize,
        value: &glib::Value,
        pspec: &glib::ParamSpec,
    ) {
        match pspec.name() {
            "video-caps" => {
                let mut settings = self.settings.lock().unwrap();
                settings.video_caps = value
                    .get::<Option<gst::Caps>>()
                    .expect("type checked upstream")
                    .unwrap_or_else(gst::Caps::new_empty);
            }
            "audio-caps" => {
                let mut settings = self.settings.lock().unwrap();
                settings.audio_caps = value
                    .get::<Option<gst::Caps>>()
                    .expect("type checked upstream")
                    .unwrap_or_else(gst::Caps::new_empty);
            }
            "stun-server" => {
                let mut settings = self.settings.lock().unwrap();
                settings.stun_server = value
                    .get::<Option<String>>()
                    .expect("type checked upstream")
            }
            "turn-server" => {
                let mut settings = self.settings.lock().unwrap();
                settings.turn_server = value
                    .get::<Option<String>>()
                    .expect("type checked upstream")
            }
            "congestion-control" => {
                let mut settings = self.settings.lock().unwrap();
                let new_heuristic = value
                    .get::<WebRTCSinkCongestionControl>()
                    .expect("type checked upstream");
                if new_heuristic != settings.cc_heuristic {
                    settings.cc_heuristic = new_heuristic;

                    let mut state = self.state.lock().unwrap();
                    for (peer_id, consumer) in state.consumers.iter_mut() {
                        match new_heuristic {
                            WebRTCSinkCongestionControl::Disabled => {
                                consumer.congestion_controller.take();
                                for encoder in &mut consumer.encoders {
                                    encoder
                                        .set_bitrate(&self.instance(), consumer.max_bitrate as i32);
                                    encoder.transceiver.set_property("fec-percentage", 50u32);
                                }
                            }
                            WebRTCSinkCongestionControl::Homegrown => {
                                let _ = consumer.congestion_controller.insert(
                                    CongestionController::new(
                                        peer_id,
                                        settings.min_bitrate,
                                        settings.max_bitrate,
                                    ),
                                );
                            }
                        }
                    }
                }
            }
            "min-bitrate" => {
                let mut settings = self.settings.lock().unwrap();
                settings.min_bitrate = value.get::<u32>().expect("type checked upstream");
            }
            "max-bitrate" => {
                let mut settings = self.settings.lock().unwrap();
                settings.max_bitrate = value.get::<u32>().expect("type checked upstream");
            }
            "do-fec" => {
                let mut settings = self.settings.lock().unwrap();
                settings.do_fec = value.get::<bool>().expect("type checked upstream");
            }
            "do-retransmission" => {
                let mut settings = self.settings.lock().unwrap();
                settings.do_retransmission = value.get::<bool>().expect("type checked upstream");
            }
            _ => unimplemented!(),
        }
    }

    fn property(&self, _obj: &Self::Type, _id: usize, pspec: &glib::ParamSpec) -> glib::Value {
        match pspec.name() {
            "video-caps" => {
                let settings = self.settings.lock().unwrap();
                settings.video_caps.to_value()
            }
            "audio-caps" => {
                let settings = self.settings.lock().unwrap();
                settings.audio_caps.to_value()
            }
            "congestion-control" => {
                let settings = self.settings.lock().unwrap();
                settings.cc_heuristic.to_value()
            }
            "stun-server" => {
                let settings = self.settings.lock().unwrap();
                settings.stun_server.to_value()
            }
            "turn-server" => {
                let settings = self.settings.lock().unwrap();
                settings.turn_server.to_value()
            }
            "min-bitrate" => {
                let settings = self.settings.lock().unwrap();
                settings.min_bitrate.to_value()
            }
            "max-bitrate" => {
                let settings = self.settings.lock().unwrap();
                settings.max_bitrate.to_value()
            }
            "do-fec" => {
                let settings = self.settings.lock().unwrap();
                settings.do_fec.to_value()
            }
            "do-retransmission" => {
                let settings = self.settings.lock().unwrap();
                settings.do_retransmission.to_value()
            }
            "stats" => self.gather_stats().to_value(),
            _ => unimplemented!(),
        }
    }

    fn signals() -> &'static [glib::subclass::Signal] {
        static SIGNALS: Lazy<Vec<glib::subclass::Signal>> = Lazy::new(|| {
            vec![
                /*
                 * RsWebRTCSink::new-webrtcbin:
                 * @peer_id: Identifier of the peer associated with the consumer added
                 * @webrtcbin: The new webrtcbin
                 *
                 * This signal can be used to tweak @webrtcbin, creating a data
                 * channel for example.
                 */
                glib::subclass::Signal::builder(
                    "new-webrtcbin",
                    &[
                        String::static_type().into(),
                        gst::Element::static_type().into(),
                    ],
                    glib::types::Type::UNIT.into(),
                )
                .build(),
            ]
        });

        SIGNALS.as_ref()
    }

    fn constructed(&self, obj: &Self::Type) {
        self.parent_constructed(obj);

        obj.set_suppressed_flags(gst::ElementFlags::SINK | gst::ElementFlags::SOURCE);
        obj.set_element_flags(gst::ElementFlags::SINK);
    }
}

impl GstObjectImpl for WebRTCSink {}

impl ElementImpl for WebRTCSink {
    fn metadata() -> Option<&'static gst::subclass::ElementMetadata> {
        static ELEMENT_METADATA: Lazy<gst::subclass::ElementMetadata> = Lazy::new(|| {
            gst::subclass::ElementMetadata::new(
                "WebRTCSink",
                "Sink/Network/WebRTC",
                "WebRTC sink",
                "Mathieu Duponchelle <mathieu@centricular.com>",
            )
        });

        Some(&*ELEMENT_METADATA)
    }

    fn pad_templates() -> &'static [gst::PadTemplate] {
        static PAD_TEMPLATES: Lazy<Vec<gst::PadTemplate>> = Lazy::new(|| {
            let caps = gst::Caps::builder("video/x-raw").build();
            let video_pad_template = gst::PadTemplate::new(
                "video_%u",
                gst::PadDirection::Sink,
                gst::PadPresence::Request,
                &caps,
            )
            .unwrap();

            let caps = gst::Caps::builder("audio/x-raw").build();
            let audio_pad_template = gst::PadTemplate::new(
                "audio_%u",
                gst::PadDirection::Sink,
                gst::PadPresence::Request,
                &caps,
            )
            .unwrap();

            vec![video_pad_template, audio_pad_template]
        });

        PAD_TEMPLATES.as_ref()
    }

    fn request_new_pad(
        &self,
        element: &Self::Type,
        templ: &gst::PadTemplate,
        _name: Option<String>,
        _caps: Option<&gst::Caps>,
    ) -> Option<gst::Pad> {
        if element.current_state() > gst::State::Ready {
            gst_error!(CAT, "element pads can only be requested before starting");
            return None;
        }

        let mut state = self.state.lock().unwrap();

        let name = if templ.name().starts_with("video_") {
            let name = format!("video_{}", state.video_serial);
            state.video_serial += 1;
            name
        } else {
            let name = format!("audio_{}", state.audio_serial);
            state.audio_serial += 1;
            name
        };

        let sink_pad = gst::GhostPad::builder_with_template(templ, Some(name.as_str()))
            .event_function(|pad, parent, event| {
                WebRTCSink::catch_panic_pad_function(
                    parent,
                    || false,
                    |sink, element| sink.sink_event(pad.upcast_ref(), element, event),
                )
            })
            .build();

        sink_pad.set_active(true).unwrap();
        sink_pad.use_fixed_caps();
        element.add_pad(&sink_pad).unwrap();

        state.streams.insert(
            name,
            InputStream {
                sink_pad: sink_pad.clone(),
                producer: None,
                in_caps: None,
                out_caps: None,
                clocksync: None,
            },
        );

        Some(sink_pad.upcast())
    }

    fn change_state(
        &self,
        element: &Self::Type,
        transition: gst::StateChange,
    ) -> Result<gst::StateChangeSuccess, gst::StateChangeError> {
        if let gst::StateChange::ReadyToPaused = transition {
            if let Err(err) = self.prepare(element) {
                gst::element_error!(
                    element,
                    gst::StreamError::Failed,
                    ["Failed to prepare: {}", err]
                );
                return Err(gst::StateChangeError);
            }
        }

        let mut ret = self.parent_change_state(element, transition);

        match transition {
            gst::StateChange::PausedToReady => {
                if let Err(err) = self.unprepare(element) {
                    gst::element_error!(
                        element,
                        gst::StreamError::Failed,
                        ["Failed to unprepare: {}", err]
                    );
                    return Err(gst::StateChangeError);
                }
            }
            gst::StateChange::ReadyToPaused => {
                ret = Ok(gst::StateChangeSuccess::NoPreroll);
            }
            gst::StateChange::PausedToPlaying => {
                let mut state = self.state.lock().unwrap();
                state.maybe_start_signaller(element);
            }
            _ => (),
        }

        ret
    }
}

impl BinImpl for WebRTCSink {}

impl ChildProxyImpl for WebRTCSink {
    fn child_by_index(&self, _object: &Self::Type, _index: u32) -> Option<glib::Object> {
        None
    }

    fn children_count(&self, _object: &Self::Type) -> u32 {
        0
    }

    fn child_by_name(&self, _object: &Self::Type, name: &str) -> Option<glib::Object> {
        match name {
            "signaller" => Some(
                self.state
                    .lock()
                    .unwrap()
                    .signaller
                    .as_ref()
                    .as_ref()
                    .clone(),
            ),
            _ => None,
        }
    }
}