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fix(recording): encode segmented video with real capture timestamps to fix white editor preview and cursor desync #1976

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fix(recording): encode segmented video with real capture timestamps to fix white editor preview and cursor desync #1976

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18 changes: 7 additions & 11 deletions crates/enc-ffmpeg/src/mux/segmented_stream.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,6 @@ pub struct SegmentedVideoEncoder {
segment_start_time: Option<Duration>,
last_frame_timestamp: Option<Duration>,
frames_in_segment: u32,
encoded_frame_count: u64,

completed_segments: Vec<VideoSegmentInfo>,

Expand Down Expand Up @@ -281,7 +280,6 @@ impl SegmentedVideoEncoder {
segment_start_time: None,
last_frame_timestamp: None,
frames_in_segment: 0,
encoded_frame_count: 0,
completed_segments: Vec::new(),
pending_segment_indices: Vec::new(),
frames_since_pending_flush: 0,
Expand Down Expand Up @@ -341,10 +339,14 @@ impl SegmentedVideoEncoder {

self.last_frame_timestamp = Some(timestamp);

let encoder_timestamp = self.next_encoder_timestamp();
// Encode with the real capture timestamp: the editor timeline, cursor
// events and the mic track are all addressed in wall-clock time, so
// frames must keep it too (WGC-style captures only deliver frames when
// the screen changes — a synthetic frame-index clock compresses those
// gaps and desyncs everything downstream). Non-monotonic capture
// timestamps are handled by normalize_input_pts inside the encoder.
self.encoder
.queue_frame(frame, encoder_timestamp, &mut self.output)?;
self.encoded_frame_count += 1;
.queue_frame(frame, timestamp, &mut self.output)?;
self.frames_in_segment += 1;

if is_first_frame {
Expand All @@ -367,12 +369,6 @@ impl SegmentedVideoEncoder {
Ok(())
}

fn next_encoder_timestamp(&self) -> Duration {
let frame_rate_num = self.codec_info.frame_rate_num.max(1) as f64;
let frame_rate_den = self.codec_info.frame_rate_den.max(1) as f64;
Duration::from_secs_f64(self.encoded_frame_count as f64 * frame_rate_den / frame_rate_num)
}

fn notify_segment(&self, event: SegmentCompletedEvent) {
if let Some(tx) = &self.segment_tx
&& let Err(e) = tx.send(event)
Expand Down
7 changes: 5 additions & 2 deletions crates/rendering/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -258,7 +258,6 @@ pub struct RecordingSegmentDecoders {
pub segment_offset: f64,
}

const SCREEN_MAX_FALLBACK_DISTANCE: u32 = 4;
const CAMERA_MAX_FALLBACK_DISTANCE: u32 = 2;

pub struct SegmentVideoPaths {
Expand Down Expand Up @@ -328,6 +327,11 @@ impl RecordingSegmentDecoders {
};

let screen_future = async {
// Screen capture is change-driven (WGC delivers nothing while the
// screen is static), so the nearest decoded frame is routinely many
// frame-times away from the requested time and is still the right
// content. Keep the default (wide) fallback distance; a tight cap
// here blanks the preview during static stretches.
spawn_decoder(
"screen",
display_path,
Expand All @@ -336,7 +340,6 @@ impl RecordingSegmentDecoders {
force_ffmpeg,
)
.await
.map(|decoder| decoder.with_max_fallback_distance(SCREEN_MAX_FALLBACK_DISTANCE))
.map_err(|e| format!("Screen:{e}"))
Comment on lines 342 to 343

@tembo tembo Bot Jul 3, 2026

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Minor maintainability thought: this relies on the decoder’s default fallback distance (currently 90). If that default ever changes again, this regression could come back; consider making the screen value explicit here.

Suggested change
.await
.map(|decoder| decoder.with_max_fallback_distance(SCREEN_MAX_FALLBACK_DISTANCE))
.map_err(|e| format!("Screen:{e}"))
.await
.map(|decoder| decoder.with_max_fallback_distance(90))
.map_err(|e| format!("Screen:{e}"))

};

Expand Down
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