From 20f25ba775880adefe18b03674d4575ce93a6031 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Tue, 8 Apr 2025 13:04:43 +0300
Subject: [PATCH] Revert "dav1ddec: Use max-frame-delay value from the decoder
 instead of calculating it"

This reverts commit 64b6661548a3bb116ece1b48a4d7bc1b254f88f7.

This needs more work because the decoder often does not know the correct
value in the beginning.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/2189>
---
 video/dav1d/src/dav1ddec/imp.rs | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/video/dav1d/src/dav1ddec/imp.rs b/video/dav1d/src/dav1ddec/imp.rs
index af05eb5e2..b7065d903 100644
--- a/video/dav1d/src/dav1ddec/imp.rs
+++ b/video/dav1d/src/dav1ddec/imp.rs
@@ -58,6 +58,7 @@ struct State {
     input_state: gst_video::VideoCodecState<'static, gst_video::video_codec_state::Readable>,
     output_info: Option<gst_video::VideoInfo>,
     video_meta_supported: bool,
+    n_cpus: usize,
 }
 
 // We make our own settings object so we don't have to deal with a Sync impl for dav1d::Settings
@@ -94,6 +95,17 @@ static CAT: LazyLock<gst::DebugCategory> = LazyLock::new(|| {
 });
 
 impl Dav1dDec {
+    // FIXME: drop this once we have API from dav1d to query this value
+    // https://code.videolan.org/videolan/dav1d/-/merge_requests/1407
+    fn estimate_frame_delay(&self, max_frame_delay: u32, n_threads: u32) -> u32 {
+        if max_frame_delay > 0 {
+            std::cmp::min(max_frame_delay, n_threads)
+        } else {
+            let n_tc = n_threads as f64;
+            std::cmp::min(8, n_tc.sqrt().ceil() as u32)
+        }
+    }
+
     fn gst_video_format_from_dav1d_picture(&self, pic: &dav1d::Picture) -> gst_video::VideoFormat {
         let bpc = pic.bits_per_component();
         let format_desc = match (pic.pixel_layout(), bpc) {
@@ -920,10 +932,14 @@ impl VideoDecoderImpl for Dav1dDec {
                             if self.obj().sink_pad().peer_query(&mut upstream_latency) {
                                 let (live, mut min, mut max) = upstream_latency.result();
                                 // For autodetection: 1 if live, else whatever dav1d gives us
-                                let frame_latency = if max_frame_delay < 0 && live {
+                                let frame_latency: u64 = if max_frame_delay < 0 && live {
                                     1
                                 } else {
-                                    state.decoder.get_frame_delay() as u64
+                                    self.estimate_frame_delay(
+                                        max_frame_delay as u32,
+                                        state.n_cpus as u32,
+                                    )
+                                    .into()
                                 };
 
                                 let fps_n = match info.fps().numer() {
@@ -1027,6 +1043,7 @@ impl VideoDecoderImpl for Dav1dDec {
             input_state: input_state.clone(),
             output_info: None,
             video_meta_supported: false,
+            n_cpus,
         });
 
         self.parent_set_format(input_state)