fmp4mux: Create FLAC dfLa box when receiving the caps too

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/2208>

mux/fmp4/src/fmp4mux/boxes.rs

@@ -1399,10 +1399,11 @@ fn write_audio_sample_entry(
             let bitrate = s.get::<i32>("bitrate").context("no ADPCM bitrate field")?;
             (bitrate / 8000) as u16
         }
-        "audio/x-flac" => with_flac_metadata(&stream.caps, |streaminfo, _| {
-            1 + ((u16::from_be_bytes([streaminfo[16], streaminfo[17]]) >> 4) & 0b11111)
-        })
-        .context("FLAC metadata error")?,
+        "audio/x-flac" => {
+            let (streamheader, _headers) =
+                flac::parse_stream_header(&stream.caps).context("FLAC streamheader")?;
+            streamheader.stream_info.bits_per_sample as u16
+        }
         _ => 16u16,
     };
 
@@ -1446,7 +1447,9 @@ fn write_audio_sample_entry(
                 write_dops(v, &stream.caps)?;
             }
             "audio/x-flac" => {
-                write_dfla(v, &stream.caps)?;
+                assert!(!stream.codec_specific_boxes.is_empty());
+                assert!(&stream.codec_specific_boxes[4..8] == b"dfLa");
+                v.extend_from_slice(&stream.codec_specific_boxes);
             }
             "audio/x-alaw" | "audio/x-mulaw" | "audio/x-adpcm" => {
                 // Nothing to do here
@@ -1673,35 +1676,6 @@ fn write_dops(v: &mut Vec<u8>, caps: &gst::Caps) -> Result<(), Error> {
     })
 }
 
-fn with_flac_metadata<R>(
-    caps: &gst::Caps,
-    cb: impl FnOnce(&[u8], &[gst::glib::SendValue]) -> R,
-) -> Result<R, Error> {
-    let caps = caps.structure(0).unwrap();
-    let header = caps.get::<gst::ArrayRef>("streamheader").unwrap();
-    let (streaminfo, remainder) = header.as_ref().split_first().unwrap();
-    let streaminfo = streaminfo.get::<&gst::BufferRef>().unwrap();
-    let streaminfo = streaminfo.map_readable().unwrap();
-    // 13 bytes for the Ogg/FLAC prefix and 38 for the streaminfo itself.
-    match <&[_; 13 + 38]>::try_from(streaminfo.as_slice()) {
-        Ok(i) if i.starts_with(b"\x7FFLAC\x01\x00") => Ok(cb(&i[13..], remainder)),
-        Ok(_) | Err(_) => bail!("Unknown streamheader format"),
-    }
-}
-
-fn write_dfla(v: &mut Vec<u8>, caps: &gst::Caps) -> Result<(), Error> {
-    write_full_box(v, b"dfLa", 0, 0, move |v| {
-        with_flac_metadata(caps, |streaminfo, remainder| {
-            v.extend(streaminfo);
-            for metadata in remainder {
-                let metadata = metadata.get::<&gst::BufferRef>().unwrap();
-                let metadata = metadata.map_readable().unwrap();
-                v.extend(&metadata[..]);
-            }
-        })
-    })
-}
-
 fn write_xml_meta_data_sample_entry(
     v: &mut Vec<u8>,
     _cfg: &super::HeaderConfiguration,
@@ -2408,6 +2382,158 @@ pub(crate) fn create_mfra(
     Ok(gst::Buffer::from_mut_slice(v))
 }
 
+/// Create FLAC `dfLa` box.
+pub(crate) fn write_dfla(caps: &gst::CapsRef) -> Result<Vec<u8>, Error> {
+    let mut dfla = Vec::new();
+
+    let (_streamheader, headers) = flac::parse_stream_header(caps).context("FLAC streamheader")?;
+
+    write_full_box(&mut dfla, b"dfLa", 0, 0, move |v| {
+        for header in headers {
+            let map = header.map_readable().unwrap();
+            v.extend(&map[..]);
+        }
+
+        Ok(())
+    })?;
+
+    Ok(dfla)
+}
+
+mod flac {
+    use anyhow::{bail, Context as _, Error};
+    use bitstream_io::FromBitStream;
+
+    #[allow(unused)]
+    #[derive(Debug, Clone)]
+    pub(crate) struct StreamHeader {
+        pub mapping_major_version: u8,
+        pub mapping_minor_version: u8,
+        pub num_headers: u16,
+        pub stream_info: StreamInfo,
+    }
+
+    impl FromBitStream for StreamHeader {
+        type Error = anyhow::Error;
+
+        fn from_reader<R: bitstream_io::BitRead + ?Sized>(r: &mut R) -> Result<Self, Self::Error>
+        where
+            Self: Sized,
+        {
+            let packet_type = r.read_to::<u8>().context("packet_type")?;
+            if packet_type != 0x7f {
+                bail!("Invalid packet type");
+            }
+            let signature = r.read_to::<[u8; 4]>().context("signature")?;
+            if &signature != b"FLAC" {
+                bail!("Invalid FLAC signature");
+            }
+
+            let mapping_major_version = r.read_to::<u8>().context("mapping_major_version")?;
+            let mapping_minor_version = r.read_to::<u8>().context("mapping_minor_version")?;
+            let num_headers = r.read_to::<u16>().context("num_headers")?;
+            let signature = r.read_to::<[u8; 4]>().context("signature")?;
+            if &signature != b"fLaC" {
+                bail!("Invalid fLaC signature");
+            }
+
+            let stream_info = r.parse::<StreamInfo>().context("stream_info")?;
+
+            Ok(StreamHeader {
+                mapping_major_version,
+                mapping_minor_version,
+                num_headers,
+                stream_info,
+            })
+        }
+    }
+
+    #[allow(unused)]
+    #[derive(Debug, Clone)]
+    pub(crate) struct StreamInfo {
+        pub min_block_size: u16,
+        pub max_block_size: u16,
+        pub min_frame_size: u32,
+        pub max_frame_size: u32,
+        pub sample_rate: u32,
+        pub num_channels: u8,
+        pub bits_per_sample: u8,
+        pub num_samples: u64,
+        pub md5: [u8; 16],
+    }
+
+    impl FromBitStream for StreamInfo {
+        type Error = anyhow::Error;
+
+        fn from_reader<R: bitstream_io::BitRead + ?Sized>(r: &mut R) -> Result<Self, Self::Error>
+        where
+            Self: Sized,
+        {
+            let _is_last = r.read_bit().context("is_last")?;
+            let metadata_block_type = r.read::<7, u8>().context("metadata_block_type")?;
+            if metadata_block_type != 0 {
+                bail!("Invalid metadata block type {metadata_block_type}");
+            }
+            let _metadata_block_size = r.read::<24, u32>().context("metadata_block_size")?;
+
+            let min_block_size = r.read_to::<u16>().context("min_block_size")?;
+            let max_block_size = r.read_to::<u16>().context("max_block_size")?;
+            let min_frame_size = r.read::<24, u32>().context("min_frame_size")?;
+            let max_frame_size = r.read::<24, u32>().context("max_frame_size")?;
+            let sample_rate = r.read::<20, u32>().context("sample_rate")?;
+            let num_channels = r.read::<3, u8>().context("num_channels")? + 1;
+            let bits_per_sample = r.read::<5, u8>().context("bits_per_sample")? + 1;
+            let num_samples = r.read::<36, u64>().context("num_samples")?;
+            let md5 = r.read_to::<[u8; 16]>().context("md5")?;
+
+            Ok(StreamInfo {
+                min_block_size,
+                max_block_size,
+                min_frame_size,
+                max_frame_size,
+                sample_rate,
+                num_channels,
+                bits_per_sample,
+                num_samples,
+                md5,
+            })
+        }
+    }
+
+    pub(crate) fn parse_stream_header(
+        caps: &gst::CapsRef,
+    ) -> Result<(StreamHeader, Vec<gst::Buffer>), Error> {
+        use bitstream_io::BitRead as _;
+
+        let s = caps.structure(0).unwrap();
+        let Ok(streamheader) = s.get::<gst::ArrayRef>("streamheader") else {
+            bail!("Need streamheader in caps for FLAC");
+        };
+
+        let Some((streaminfo, remainder)) = streamheader.as_ref().split_first() else {
+            bail!("Empty FLAC streamheader");
+        };
+        let streaminfo = streaminfo.get::<&gst::Buffer>().unwrap();
+        let map = streaminfo.map_readable().unwrap();
+
+        let mut reader = bitstream_io::BitReader::endian(
+            std::io::Cursor::new(map.as_slice()),
+            bitstream_io::BigEndian,
+        );
+
+        let header = reader
+            .parse::<StreamHeader>()
+            .context("Parsing FLAC streamheader")?;
+
+        Ok((
+            header,
+            std::iter::once(gst::Buffer::from_mut_slice(Vec::from(&map[13..])))
+                .chain(remainder.iter().map(|v| v.get::<gst::Buffer>().unwrap()))
+                .collect::<Vec<_>>(),
+        ))
+    }
+}
+
 /// Create AC-3 `dac3` box.
 pub(crate) fn create_dac3(buffer: &gst::BufferRef) -> Result<Vec<u8>, Error> {
     use bitstream_io::{BitRead as _, BitWrite as _};

mux/fmp4/src/fmp4mux/imp.rs

@@ -3568,14 +3568,17 @@ impl FMP4Mux {
                 }
                 "audio/x-flac" => {
                     discard_header_buffers = true;
-                    if let Err(e) = s.get::<gst::ArrayRef>("streamheader") {
-                        gst::error!(
-                            CAT,
-                            obj = pad,
-                            "Muxing FLAC into MP4 needs streamheader: {}",
-                            e
-                        );
-                        return Err(gst::FlowError::NotNegotiated);
+
+                    codec_specific_boxes = match boxes::write_dfla(&caps) {
+                        Ok(boxes) => boxes,
+                        Err(err) => {
+                            gst::error!(
+                                CAT,
+                                obj = pad,
+                                "Failed to create FLAC codec specific box: {err}"
+                            );
+                            return Err(gst::FlowError::NotNegotiated);
+                        }
                     };
                 }
                 "audio/x-ac3" | "audio/x-eac3" => {