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fix(enc-ffmpeg): use encoder_time_base in H264PacketEncoder to fix 4-8x playback speed #1970

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Merged
richiemcilroy merged 1 commit into from
Jul 2, 2026
+8 −4
Merged

fix(enc-ffmpeg): use encoder_time_base in H264PacketEncoder to fix 4-8x playback speed #1970

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12 changes: 8 additions & 4 deletions crates/enc-ffmpeg/src/video/h264_packet.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -198,16 +198,20 @@ impl H264PacketEncoder {
}

fn update_pts(&mut self, frame: &mut frame::Video, timestamp: Duration) {
// Use encoder_time_base (the value sent to the muxer subprocess via InitVideo),
// NOT self.encoder.time_base() which may be overridden by the codec after open.
// Mismatching these causes the muxer to rescale PTS using the wrong time base,
// producing wrong playback speed (observed as 4-8x too fast with h264_videotoolbox).
let tb = self.encoder_time_base;
if timestamp != Duration::MAX {
let tb = self.encoder.time_base();
let rate = tb.denominator() as f64 / tb.numerator() as f64;

@tembo tembo Bot Jul 2, 2026

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tb is now coming from config (vs the post-open codec), so it might be worth guarding against an invalid/zero Rational here — otherwise rate can become inf/NaN and the float->int cast can silently produce huge PTS.

Suggested change
let rate = tb.denominator() as f64 / tb.numerator() as f64;
debug_assert!(
tb.numerator() > 0 && tb.denominator() > 0,
"invalid encoder_time_base"
);
let rate = tb.denominator() as f64 / tb.numerator() as f64;

let pts = (timestamp.as_secs_f64() * rate).round() as i64;
let first_pts = *self.first_pts.get_or_insert(pts);
let pts = normalize_input_pts(
pts - first_pts,
self.last_frame_pts,
tb,
self.encoder.frame_rate(),
self.frame_rate,
);
self.last_frame_pts = Some(pts);
frame.set_pts(Some(pts));
Expand All @@ -216,8 +220,8 @@ impl H264PacketEncoder {
let pts = normalize_input_pts(
pts - first_pts,
self.last_frame_pts,
self.encoder.time_base(),
self.encoder.frame_rate(),
tb,
self.frame_rate,
);
self.last_frame_pts = Some(pts);
frame.set_pts(Some(pts));
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