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fix(rendering): FFmpeg decoder seeks instead of guessing on backward cache misses #2665

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Merged
richiemcilroy merged 2 commits into from
Oct 17, 2026
Merged

fix(rendering): FFmpeg decoder seeks instead of guessing on backward cache misses #2665

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d537fae
fix(rendering): FFmpeg decoder seeks instead of guessing on backward …
richiemcilroy Oct 17, 2026
b5822c3
style: cargo fmt
richiemcilroy Oct 17, 2026
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115 changes: 39 additions & 76 deletions crates/rendering/src/decoder/ffmpeg.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,6 @@ struct PendingRequest {
reply: oneshot::Sender<DecodedFrame>,
}

const MAX_FRAME_LOOKBACK_TOLERANCE: u32 = 2;
const MAX_FRAME_CACHE_BYTES: usize = 128 * 1024 * 1024;
/// Cache weight of a frame still on the GPU (it pins an NVDEC surface).
#[cfg(target_os = "linux")]
Expand Down Expand Up @@ -765,24 +764,28 @@ impl FfmpegDecoder {
continue;
}

if is_backward_seek {
let best_cached_frame = sw_cache
.range(..=requested_frame)
.next_back()
.filter(|(k, _)| {
requested_frame.saturating_sub(**k) <= MAX_FRAME_LOOKBACK_TOLERANCE
})
.map(|(k, _)| *k);

if let Some(frame_num) = best_cached_frame
&& let Some(cached) = sw_cache.get_mut(&frame_num)
{
let data = cached.produce(&mut sw_converter);
// Requests inside a KNOWN pts hole are answered with the
// hole's start frame — the true VFR hold — without
// touching the decoder; see the hardware path below.
if let Some(hole_start) = sw_pts_holes
.range(..=requested_frame)
.next_back()
.filter(|&(_, &end)| requested_frame < end)
.map(|(&start, _)| start)
{
let data = sw_cache
.get_mut(&hole_start)
.map(|c| c.produce(&mut sw_converter))
.or_else(|| sw_gap_hold.clone().filter(|h| h.number == hole_start));
if let Some(data) = data {
sw_gap_hold = Some(data.clone());
*sw_last_sent_frame.borrow_mut() = Some(data.clone());
let _ = reply.send(data.frame);
continue;
}
}

if is_backward_seek {
if let Err(error) = sw_this.reset(requested_time)
&& let Some(control) = &managed
{
Expand All @@ -799,28 +802,6 @@ impl FfmpegDecoder {
sw_reader_at = None;
}

// Requests inside a KNOWN pts hole are answered with the
// hole's start frame — the true VFR hold — without
// touching the decoder; see the hardware path above.
if !is_backward_seek
&& let Some(hole_start) = sw_pts_holes
.range(..=requested_frame)
.next_back()
.filter(|&(_, &end)| requested_frame < end)
.map(|(&start, _)| start)
{
let data = sw_cache
.get_mut(&hole_start)
.map(|c| c.produce(&mut sw_converter))
.or_else(|| sw_gap_hold.clone().filter(|h| h.number == hole_start));
if let Some(data) = data {
sw_gap_hold = Some(data.clone());
*sw_last_sent_frame.borrow_mut() = Some(data.clone());
let _ = reply.send(data.frame);
continue;
}
}

if reply.is_closed() {
continue;
}
Expand Down Expand Up @@ -1348,24 +1329,33 @@ impl FfmpegDecoder {
continue;
}

if is_backward_seek {
let best_cached_frame = cache
.range(..=requested_frame)
.next_back()
.filter(|(k, _)| {
requested_frame.saturating_sub(**k) <= MAX_FRAME_LOOKBACK_TOLERANCE
})
.map(|(k, _)| *k);

if let Some(frame_num) = best_cached_frame
&& let Some(cached) = cache.get_mut(&frame_num)
{
let data = cached.produce(&mut converter);
// Requests inside a KNOWN pts hole are answered with the
// hole's start frame — the true VFR hold (the frame simply
// stayed on screen) — without touching the decoder. This
// keeps the post-hole frames cached and the reader parked,
// however long the hole runs. Only recorded holes qualify: a
// bare "some cached frame lies beyond the request" test would
// also match disjoint cache islands left by seeks, and
// serving stale content there would freeze playback.
if let Some(hole_start) = pts_holes
.range(..=requested_frame)
.next_back()
.filter(|&(_, &end)| requested_frame < end)
.map(|(&start, _)| start)
{
let data = cache
.get_mut(&hole_start)
.map(|c| c.produce(&mut converter))
.or_else(|| gap_hold.clone().filter(|h| h.number == hole_start));
if let Some(data) = data {
gap_hold = Some(data.clone());
*last_sent_frame.borrow_mut() = Some(data.clone());
let _ = reply.send(data.frame);
continue;
}
}

if is_backward_seek {
if let Err(error) = this.reset(requested_time)
&& let Some(control) = &managed
{
Expand All @@ -1383,33 +1373,6 @@ impl FfmpegDecoder {
reader_at = None;
}

// Requests inside a KNOWN pts hole are answered with the
// hole's start frame — the true VFR hold (the frame simply
// stayed on screen) — without touching the decoder. This
// keeps the post-hole frames cached and the reader parked,
// however long the hole runs. Only recorded holes qualify: a
// bare "some cached frame lies beyond the request" test would
// also match disjoint cache islands left by seeks, and
// serving stale content there would freeze playback.
if !is_backward_seek
&& let Some(hole_start) = pts_holes
.range(..=requested_frame)
.next_back()
.filter(|&(_, &end)| requested_frame < end)
.map(|(&start, _)| start)
{
let data = cache
.get_mut(&hole_start)
.map(|c| c.produce(&mut converter))
.or_else(|| gap_hold.clone().filter(|h| h.number == hole_start));
if let Some(data) = data {
gap_hold = Some(data.clone());
*last_sent_frame.borrow_mut() = Some(data.clone());
let _ = reply.send(data.frame);
continue;
}
}

if reply.is_closed() {
continue;
}
Expand Down
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