fix(webrtc): force IDR on KeyframeRequest via forced-idr=1 + pict_type (closes #16)
WebRTC KeyframeRequest 响应延迟 2.1s（152 P 帧丢弃）→ 端到端 5-20ms。 - BitrateCommand::ForceKeyframe variant over existing bitrate_tx channel - SwEncEncode.force_keyframe_pending: bypass dedup, set AV_PICTURE_TYPE_I, clear only after avcodec_send_frame succeeds - libx264 forced-idr=1 via av_opt_set (FFmpeg-level option, not x264-native) - pict_type reset to NONE per frame (reused AVFrame leak guard) - WebRtcInner.force_keyframe_to_encode + take_force_keyframe() drain API - recreate_encoder sets force_keyframe_pending (resolution change → IDR) Verification: skipping non-IDR frame 152→0, ForceKeyframe→IDR 4-5ms stable.
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dailz
+38
-1
@@ -25,6 +25,9 @@ use crate::transform::{transpose_if_transform_transposed, Transform};
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pub enum BitrateCommand {
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UpdateBitrate { target_bps: u64 },
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UpdateResolution { width: u32, height: u32 },
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/// Force the next encoded frame to be an IDR. Sent by the WebRTC thread
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/// in response to str0m `Event::KeyframeRequest` or a resolution change.
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ForceKeyframe,
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}
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#[derive(Clone, Copy, Debug)]
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@@ -856,6 +859,7 @@ impl SwEncImport {
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requested = Some((width & !1, height & !1));
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}
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BitrateCommand::UpdateBitrate { .. } => {}
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BitrateCommand::ForceKeyframe => {}
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}
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}
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@@ -966,6 +970,10 @@ pub struct SwEncEncode {
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fps: u32,
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bitrate: u64,
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gop_size: u32,
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/// Set true when WebRTC requests a keyframe. Forces the next frame to
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/// `AV_PICTURE_TYPE_I` and bypasses the dedup hash check. Cleared only
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/// after `avcodec_send_frame` accepts the forced frame.
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force_keyframe_pending: bool,
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}
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const FNV1A_OFFSET_BASIS: u64 = 0xcbf29ce484222325;
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@@ -1028,6 +1036,7 @@ impl SwEncEncode {
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fps,
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bitrate,
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gop_size,
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force_keyframe_pending: false,
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})
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}
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@@ -1066,6 +1075,7 @@ impl SwEncEncode {
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fps,
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bitrate,
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gop_size,
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force_keyframe_pending: false,
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})
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}
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@@ -1103,8 +1113,14 @@ impl SwEncEncode {
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}
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}
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BitrateCommand::UpdateResolution { .. } => {}
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BitrateCommand::ForceKeyframe => {
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self.force_keyframe_pending = true;
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tracing::debug!("encode thread: ForceKeyframe requested");
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}
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}
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}
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let force_this_frame = self.force_keyframe_pending;
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while let Ok(change) = self.resolution_rx.try_recv() {
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self.recreate_encoder(change.width, change.height)?;
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@@ -1130,7 +1146,7 @@ impl SwEncEncode {
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self.frame_count = self.frame_count.saturating_add(1);
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let current_hash = hash_sampled_y_plane(&frame.y_data, width, height, frame.y_stride);
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let force_gop_frame = self.gop_size > 0 && frame_index % u64::from(self.gop_size) == 0;
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if frame_index > 0 && !force_gop_frame && current_hash == self.last_frame_hash {
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if frame_index > 0 && !force_gop_frame && !force_this_frame && current_hash == self.last_frame_hash {
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tracing::debug!(frame_index, "skipping duplicate frame");
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self.last_frame_hash = current_hash;
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return Ok(());
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@@ -1172,8 +1188,16 @@ impl SwEncEncode {
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let start_ts = self.starting_timestamp.unwrap_or(0);
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// SAFETY: yuv_frame is initialized, writable, and matches the opened encoder format.
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// pict_type is reset every frame: the AVFrame is reused, so without resetting to NONE
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// a previously-forced I-type would leak into subsequent P-frames. With forced-idr=1
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// set on the encoder, AV_PICTURE_TYPE_I produces a true IDR NALU.
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unsafe {
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(*self.yuv_frame).pts = pts;
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(*self.yuv_frame).pict_type = if force_this_frame {
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ffi::AVPictureType::AV_PICTURE_TYPE_I
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} else {
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ffi::AVPictureType::AV_PICTURE_TYPE_NONE
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};
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let ret = ffi::avcodec_send_frame(self.enc_video.as_mut_ptr(), self.yuv_frame);
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if ret < 0 {
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bail!(
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@@ -1183,6 +1207,10 @@ impl SwEncEncode {
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}
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}
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if force_this_frame {
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self.force_keyframe_pending = false;
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}
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self.drain_encoder(start_ts)
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}
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@@ -1215,6 +1243,7 @@ impl SwEncEncode {
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self.enc_height = height;
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self.last_frame_hash = 0;
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self.frame_count = 0;
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self.force_keyframe_pending = true;
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Ok(())
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}
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@@ -1741,6 +1770,14 @@ fn create_software_h264_encoder(
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// avcodec_alloc_context3. Setting level is a simple i32 field
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// assignment on a properly aligned struct.
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(*enc.as_mut_ptr()).level = 42; // H.264 Level 4.2 (up to 1440p@30)
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// SAFETY: priv_data belongs to the unopened libx264 encoder context.
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// `forced-idr` is an FFmpeg-level private option (not x264-native),
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// so it must be set via av_opt_set, NOT via the x264opts string.
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// With forced-idr=1, setting AV_PICTURE_TYPE_I on an input frame
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// produces a true IDR NALU with inline SPS/PPS (repeat_headers=1).
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let key = CString::new("forced-idr").unwrap();
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let val = CString::new("1").unwrap();
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ffi::av_opt_set((*enc.as_mut_ptr()).priv_data, key.as_ptr(), val.as_ptr(), 0);
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let key = CString::new("x264opts").unwrap();
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let vbv_maxrate = bitrate;
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let vbv_bufsize = bitrate / 4;
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@@ -702,6 +702,10 @@ fn webrtc_thread_loop(
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break;
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}
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if wrtc.take_force_keyframe() {
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let _ = bitrate_tx.try_send(BitrateCommand::ForceKeyframe);
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}
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let connected = wrtc.is_connected();
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let was_paused = paused.load(Ordering::Relaxed);
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let now_paused = !connected;
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@@ -200,6 +200,7 @@ struct WebRtcInner {
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video_pt: Option<Pt>,
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connected: bool,
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need_keyframe: bool,
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force_keyframe_to_encode: bool,
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current_bwe_estimate: Option<Bitrate>,
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rtp_clock: u32,
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buf: Vec<u8>,
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@@ -353,6 +354,17 @@ impl WebRtcState {
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pub fn set_need_keyframe(&mut self) {
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if let Some(inner) = self.inner.as_mut() {
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inner.need_keyframe = true;
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inner.force_keyframe_to_encode = true;
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}
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}
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pub fn take_force_keyframe(&mut self) -> bool {
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if let Some(inner) = self.inner.as_mut() {
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let v = inner.force_keyframe_to_encode;
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inner.force_keyframe_to_encode = false;
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v
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} else {
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false
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}
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}
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}
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@@ -429,6 +441,7 @@ impl WebRtcInner {
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video_pt: None,
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connected: false,
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need_keyframe: false,
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force_keyframe_to_encode: false,
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current_bwe_estimate: None,
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rtp_clock: 0,
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buf: vec![0u8; 65535],
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@@ -446,6 +459,7 @@ impl WebRtcInner {
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.map_err(|e| anyhow::anyhow!("accept_offer: {e}"))?;
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self.need_keyframe = true;
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self.force_keyframe_to_encode = true;
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tracing::info!("SDP exchange complete, waiting for ICE/DTLS...");
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self.discover_video_params();
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@@ -503,6 +517,7 @@ impl WebRtcInner {
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tracing::info!("WebRTC connected!");
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self.connected = true;
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self.need_keyframe = true;
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self.force_keyframe_to_encode = true;
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self.discover_video_params();
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}
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Event::IceConnectionStateChange(IceConnectionState::Disconnected) => {
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@@ -525,6 +540,7 @@ impl WebRtcInner {
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Event::KeyframeRequest(_) => {
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tracing::info!("received keyframe request from viewer");
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self.need_keyframe = true;
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self.force_keyframe_to_encode = true;
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}
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Event::EgressBitrateEstimate(est) => {
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let bitrate = match est {
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