perf(audio): stretch speed regions through libavfilter atempo instead of WSOLA — fixes exports frozen at ~80% - #371
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… of WSOLA WSOLA is O(grain x search-radius) per rendered sample. On a long clip with speed regions (measured: 65.4M samples after speed-segment quantization) it runs for many minutes at 100% of one core, and the export appears frozen at ~80% progress — audio stretching is the pipeline's last big job. Users kill the export; nothing fails, it is just unreachably slow. Route stretch_pcm_to_length through an in-process abuffer -> atempo -> abuffersink graph instead. atempo is the same pitch-preserving time-stretch, but O(n) with ffmpeg's SIMD routines: the same input takes seconds. avfilter already ships in the app — fetch-ffmpeg.mjs vendors every av*.dll of the BtbN LGPL-shared build, and the addon sits beside those DLLs — so this only links a library that was already in the box. - build.rs: link avfilter (bindgen already allowlists avfilter_*/ via the existing "av.*" filter, and the Linux osff_ symbol-rename table derives from the soname list) - build-linux-compositor-addon.mjs: stage libavfilter.so.11 alongside the other renamed libs - wrappers: include libavfilter headers - audio.rs: avfilter_atempo_stretch() mounts the graph, feeds planar f32 chunks, drains, and pads/truncates to the exact target length; speeds outside atempo's [0.5, 100] window chain multiple stages (0.2 -> atempo=0.5,atempo=0.5,atempo=0.8). Any failure returns None and falls back to the existing WSOLA path unchanged. - sink negotiation may yield flt (interleaved) or fltp (planar); both are deinterleaved into PlanarPcm Verified with cargo test: a 10 s 440 Hz stereo sine at speed 1.25 returns exactly 8 s and measures 440 Hz +/- 2 Hz by zero crossings (pitch preserved — a plain resample would shift it).
Two hardening guards found while diagnosing the slow-export hang: - decode_clip_audio: a container whose audio track is truncated or corrupt at the end can keep av_read_frame from ever returning AVERROR_EOF, so decoder_eof never propagates and the demux loop spins at 100% CPU forever. Cap it with a 60 s time budget — time, not iterations, because av_read_frame can be slow on a corrupt stream and an iteration cap would either never trigger or cut healthy long clips short. - WsolaTimeStretcher::process: if find_best_delta keeps returning a delta that puts grain_pos back where it was, the buf_end break is never reached and the loop spins forever. Detect the stagnation (100 consecutive non-advancing grains) and force the exit — the fallback path after the previous commit's atempo change, so this only protects the unlikely case where WSOLA still runs.
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📝 WalkthroughWalkthroughThe compositor adds public audio finalization, FFmpeg ChangesAudio time-stretching
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to No actionable merge-blocking risk remains. The PR is merge-ready after normal review, with minor follow-up recommended to correct documentation of progress timing and audio sample-format handling. Sequence Diagram(s)sequenceDiagram
participant stretch_pcm_to_length
participant FFmpegFilterGraph
participant WSOLA
stretch_pcm_to_length->>FFmpegFilterGraph: Process PCM with chained atempo filters
FFmpegFilterGraph-->>stretch_pcm_to_length: Return sufficient output or failure
stretch_pcm_to_length->>WSOLA: Use fallback when FFmpeg processing fails or returns insufficient output
Suggested reviewers: 🚥 Pre-merge checks | ✅ 3 | ❌ 2❌ Failed checks (2 warnings)
✅ Passed checks (3 passed)
Full details: Description checkExplanation The description explains the problem, root cause, implementation, fallback behavior, and testing results. However, it does not follow the repository template and omits the required Summary, Related issue, Type of change, Release impact, Desktop impact, and Screenshots / video sections. Resolution Rewrite the description using all template headings. Add a Summary, provide a related issue reference or state that none applies, select the applicable change type, release impact, and desktop impact checkboxes, mark Screenshots / video as not applicable if appropriate, and retain the existing Testing details. Full details: Docstring CoverageExplanation Docstring coverage is 72.73% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 4 files. (4 skipped: 4 unsupported.) ✨ Finishing Touches🧪 Generate unit tests (beta)
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Inline comments:
In `@crates/compositor/src/audio.rs`:
- Around line 284-305: Update the decode loop budget near loop_start and
loop_budget so it scales with the requested window duration while retaining a
minimum floor, rather than using a fixed 60-second limit. Derive the duration
from the existing window or source timing symbols, preserve the timeout’s
guaranteed termination and forced decoder_eof behavior, and keep the existing
timeout logging and loop flow intact.
- Around line 986-1044: Update the atempo drain logic around
av_buffersrc_add_frame and av_buffersink_get_frame to check and propagate
non-AVERROR_EOF/AVERROR_EAGAIN failures as None instead of padding them with
silence. Track the flush result, classify sink returns correctly, and reject
implausibly short stretched output so stretch_pcm_to_length uses the WSOLA
fallback; preserve normal EOF/EAGAIN completion and exact resize behavior for
valid output.
In `@crates/compositor/wrapper_macos.h`:
- Around line 20-22: Separate the concatenated libswscale and libavfilter
include directives in the macOS wrapper so each `#include` occupies its own line,
preserving the existing buffersrc and buffersink includes.
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- wrapper_macos.h: the appended avfilter include landed on the same line as the trailing swscale include (the file had no final newline), so the preprocessor never saw it — split them onto separate lines. macOS builds would have produced no avfilter bindings at all. - decode budget: scale with the requested window (x8, floor 60 s) instead of a flat 60 s, so slow storage / heavy codecs decoding a long window are not cut off into trailing silence. - atempo drain: only AVERROR_EOF / AVERROR_EAGAIN are benign; any other negative return is a real filter failure — return None so the WSOLA fallback runs instead of exporting partial audio padded with silence. The buffersrc flush return is checked for the same reason.
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Revue ciblée sur les points bloquants uniquement — la direction de la PR me paraît bonne (le chemin WSOLA est réellement pathologique, et atempo est le bon outil), mais trois défauts produisent du silence audio ou une app non chargeable, tous sans remontée à l'UI.
audio.rs:1058— un span de moins de 1024 échantillons fait sortiratempoà vide ; leresizeconvertit ça en silence numérique retourné comme un succès, donc le fallback WSOLA est inatteignable. Reachable via n'importe quel écart entre deux speed regions.audio.rs:292-299— la sortie forcée fabrique un EOF au lieu d'échouer (clip muet dans un export « réussi »), le budget est dimensionné sur la fenêtre de trim alors que le travail dépend de la distance de seek, et il n'a pas de plafond : il s'auto-désactive sur les conteneurs à durée inconnue, soit exactement le cas visé.build.rs:72—avfilterentre dans la table d'import de l'addon, mais la sonde « déjà vendored » defetch-ffmpeg.mjset les trois gardes debefore-pack.cjsne le connaissent pas : un workspace tiède ou un build partiel livre un addon qui meurt àrequire().
Détail et scénarios de reproduction dans les commentaires inline.
Deux notes hors bloquants, pour la suite : atempo est appelé au-dessus du passthrough PASSTHROUGH_EPSILON de WSOLA, donc tout span 1× de plus de ~33 s @30 fps (~17 s @60 fps) est désormais resynthétisé là où c'était un copy_from_slice — remonter ce test au-dessus de la ligne 782 le règle. Et le « figé à ~80 % » est en partie un défaut de reporting : on_clip_end fait décodage + stretch en synchrone sur le thread de rendu sans jamais appeler progress().
Generated by Claude Code
- getopenscreen#1: avfilter_atempo_stretch returns None (-> WSOLA fallback) when atempo drains fewer than 90% of target samples, instead of padding the near-empty output to target_samples and exporting silence on short speed spans (gaps between regions, single video frames). - getopenscreen#3: avfilter is now a fully-known vendoring/packaging dependency: * fetch-ffmpeg.mjs probes ALL six shared DLLs (was: any av*.dll) so a warm tree with the five pre-avfilter DLLs re-vendors avfilter-11.dll. * before-pack.cjs lists avfilter on Linux, Windows and macOS (mac atLeast 3 -> 4). * build-linux-compositor-addon.mjs header + build-and-packaging.md note the sixth ffmpeg soname. - getopenscreen#2 (decode loop budget guard) removed here and split into its own PR to keep this one single-concern (atempo stretch).
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@EtienneLescot thanks for the detailed review — all three blockers are addressed in the updated head
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Inline comments:
In `@scripts/before-pack.cjs`:
- Around line 79-83: Update scripts/before-pack.cjs lines 79-83 to require
libswresample and libswscale with separate checks so duplicate versions cannot
satisfy the count; update scripts/before-pack.cjs lines 237-242 to add
swresample and swscale to the Windows DLL requirements; update
technical-documentation/engineering/build-and-packaging.md line 207 to document
all six required FFmpeg dylib families.
In `@scripts/fetch-ffmpeg.mjs`:
- Around line 425-435: Update fetchSharedDlls to ensure binDir exists before
calling fs.readdirSync for vendoredFiles, including the --sdk-only path. Create
the directory recursively and preserve the existing vendored DLL detection
behavior.
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…ll six ffmpeg libs, guard --sdk-only - before-pack.cjs macOS: split the combined av* regex (atLeast: 4) into one requirement per library — avcodec/avformat/avutil/swresample/swscale/avfilter — matching the LINUX_REQUIRED style so duplicate versions of one library cannot satisfy the count while another is missing. - before-pack.cjs Windows: add swresample/swscale to the required DLL list (was: avcodec/avformat/avutil/avfilter). - build-and-packaging.md: document all six dylib families in the macOS guard table. - fetch-ffmpeg.mjs: create binDir before readdirSync in fetchSharedDlls, so the --sdk-only path no longer throws on a fresh checkout (binDir is normally created by the CLI branch before the shared-DLL fetch).
build.rs prefixes every av* function in ffi.rs, so the atempo path makes
the addon import osff_avfilter_graph_alloc, osff_av_buffersrc_add_frame
and friends. preBuild only staged lib{avformat,avcodec,avutil,swscale,
swresample}, so no libavfilter.so was renamed and no unversioned symlink
existed for -lavfilter: the build either failed to link or bound against
nixpkgs' unrenamed copy. installPhase's leak check does not catch that --
it only rejects names that are NOT osff_-prefixed -- so the derivation
succeeded and require() failed at runtime with "undefined symbol:
osff_avfilter_graph_alloc", leaving compositorViewService as a no-op and
preview plus every export dead on the whole NixOS package.
Add avfilter to the staged set, matching the six libraries
crates/compositor/build.rs links and scripts/build-linux-compositor-addon.mjs
already ships. Both filters keep working unchanged: avfilter's exports are
av-prefixed (avfilter_*, av_buffersrc_*, av_buffersink_*), so the preBuild
awk and the installPhase leak check already cover them. Also corrects the
installPhase comment that counted five direct DT_NEEDED libraries.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
export-pipeline.md and native-compositor.md still said WSOLA stretches each speed sub-segment. atempo is now the primary path and WSOLA is the fallback stretch_pcm_to_length takes when the filter graph cannot be built, configured or run, or when it drains under 90% of the target samples on a span shorter than atempo's analysis window. export-pipeline.md also claimed the stretch "is kicked off before the video loop so it overlaps the encode and does not add to the wall". It does not: decode and stretch run synchronously in walk_composited_timeline's on_clip_end callback, which fires once per clip after that clip's frames are encoded, on the same thread -- and progress() is driven only by encoded video frames, so nothing moves while the stretch runs. Describe the real shape, which is also why the O(n) atempo path matters. build-and-packaging.md named avcodec/avformat/avutil as the addon's ffmpeg dependencies. build.rs links six -- avcodec, avformat, avutil, swresample, swscale, avfilter -- and before-pack.cjs now requires each of them individually on all three platforms. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Inline comments:
In `@technical-documentation/architecture/export-pipeline.md`:
- Around line 78-84: Update the export-pipeline timing description to state that
progress is driven by composed timeline frames, not only encoded frames. Explain
that encoding may lag by the readback ring, and that the final readback drain
occurs after the timeline walk, so the last composed frame can still be pending
when stretching begins.
In `@technical-documentation/architecture/native-compositor.md`:
- Around line 202-208: Update the speed-region description around
avfilter_atempo_stretch to state that abuffer is configured for fltp/48
kHz/stereo, while the unconstrained abuffersink may produce either FLTP or FLT;
document that the drain path accepts both and normalizes them to planar PCM,
replacing the claims that atempo preserves format and performs no conversion.
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The atempo swap is the right instinct and the factor-chaining is neatly done. Two things before this can merge, though, and one of them I need you to check because I couldn't build it.
I pushed two commits to your branch (8dc0483, 01e991c), since "allow edits from maintainers" is on.
The first is the one that worries me. nix/compositor-view.nix builds its symbols.map from a five-library glob, and build.rs prefixes every av* function — so your new code makes the addon import osff_avfilter_graph_alloc, osff_av_buffersrc_add_frame and friends, which that glob never defines. The build either fails on cannot find -lavfilter or links against nixpkgs' unrenamed copy and ships a .node with undefined symbols; the installPhase leak check only flags names without the osff_ prefix, so it passes either way. With nixpkgs' default -z now, require() then fails, compositorViewService logs "native addon not present; running as no-op", and preview plus every export are dead on the whole NixOS/AUR package. You updated scripts/build-linux-compositor-addon.mjs for exactly this; nix/ was missed.
I could not verify that fix — there's no nix on my machine, so it isn't even parse-checked. Please have someone run nix build before merging, and confirm two things: that nixpkgs' ffmpeg .lib output actually contains libavfilter.so.*, and that the case "$lib" in *.so.*.*) continue ;; esac filter still leaves exactly one libavfilter.so.<major>.
The second commit is documentation — export-pipeline.md, native-compositor.md and engineering/build-and-packaging.md still described the WSOLA world and the three-library ffmpeg set. Note export-pipeline.md:74 claimed the stretch "is kicked off before the video loop so it overlaps the encode", which isn't what the code does; that's the progress comment below.
Still stale and out of scope: .github/workflows/ci.yml:116 lists only five libraries in a prose comment (harmless — Homebrew's ffmpeg ships avfilter).
The rest, on lines outside the diff hunks:
crates/compositor/src/audio.rs:766 — I don't think atempo actually fixes the freeze — it routes around it, and every remaining fallback still hits it.
The cost is here: stretch_pcm_to_length feeds the entire region into stretcher.push(pcm), so self.buf holds all source samples, and then every grain does self.buf[channel] = self.buf[channel][drop..].to_vec() plus the same on self.mono — reallocating and copying the whole remaining buffer while it shrinks by only ha (~960-1920) samples per grain.
For the 65.4M-sample export you cite that's roughly N²/(2·ha) ≈ 1.1e12 f32 per channel, ~9TB of memcpy, which dominates find_best_delta by about 7x. Your diagnosis at :794 names the per-sample search cost, which is the smaller term.
A VecDeque or a read offset would fix it in a few lines — and it would also fix the WSOLA path that's still reached when avfilter is missing, when graph_config fails, and on the new 90% bail at :1078.
crates/compositor/src/pipeline_windows.rs:1436 — Progress is still driven only by encoded video frames, so "frozen at ~80%" comes back whenever this path is slow.
progress(frame_index + 1) fires from the video walk callback at :1427, while stretch_clip_pcm_by_speed runs synchronously here with no reporting at all. The bar stops at whatever fraction the clip's frames reached and sits there for the whole stretch.
atempo shortens that from minutes to seconds, which is a real improvement — but a long clip, a fallback to WSOLA, or any future audio stage reproduces the symptom exactly. Since the PR is named after that bug, reporting progress across the audio phase seems worth doing here rather than leaving it to the next report.
The three blocking findings from the 27/08 review, plus the packaging invariant that keeps the six-library set from drifting again. atempo does not render exactly n/tempo samples: it falls short by a fixed amount per chain, independent of input length — 217 samples for one stage, ~2 700 for four, i.e. up to 56 ms at 0.1x. Pushing more input does not recover it, and zero-filling it left a hard silence gap butt-joined to the next segment, since the equal-power crossfade covers clip boundaries only. A first pass now measures the shortfall on the real content without keeping anything and a second asks for `target + shortfall`; measured across the whole editor speed ladder on spans of 0.05s to 3s, the trailing silence is now zero samples everywhere. Above 1x the shortfall is zero and the second pass is skipped. The chain is pinned to flt rather than fltp. af_atempo advertises packed formats only, so a planar abuffer made the negotiation insert an aresample and left the planar drain branch unreachable — the sink was already handing back AV_SAMPLE_FMT_FLT. Asking for flt on both ends leaves no conversion filter in the graph. The drain is interleaved with the feed. av_buffersrc_add_frame does not pull the graph, so pushing a whole region first queued all of it in the buffersrc — half a gigabyte on a 20-minute stereo region. The 90% threshold is gone. It padded up to a tenth of a region with silence above the line and fell back to WSOLA without a word below it; every fallback now logs its reason. WSOLA, still the fallback, no longer copies the remaining buffer on every grain. `discard_below` advances a read cursor and compacts only when the consumed head passes the remainder, which takes the total from O(N^2) to O(N): a measured export that ran over ten minutes without finishing now takes ~90 s, and the output is bit-identical at 0.25x/0.5x/1.25x/2x. Its stagnation guard is dropped: search_target grows by ha > 0 every iteration so the buf_end break always fires, and had the guard tripped it would have truncated the region into silence. scripts/ffmpeg-linked-libraries.test.mjs derives the linked set from build.rs and checks fetch-ffmpeg.mjs, before-pack.cjs (three tables), build-linux-compositor-addon.mjs and nix/compositor-view.nix against it — the nix glob especially, which no PR check builds.
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I've taken the branch over and pushed The silence hole. The chain is pinned to The drain is interleaved with the feed. The 90% threshold is gone. It padded up to a tenth of a region with silence above the line and fell back to WSOLA without a word below it. Every fallback path now logs its reason. WSOLA is no longer quadratic. This was the bigger half of the freeze you diagnosed: The WSOLA stagnation guard is dropped rather than fixed: Cost, release build, 5 minutes of source: atempo 0.6 s vs WSOLA 20 s at 1.25×; 4.9 s vs 55 s at 0.25× (two passes). Packaging. Still open: the nix derivation. That test catches glob drift, which is the mistake that actually happened, but it is not Out of scope and tracked separately: progress is still driven only by composed video frames, so the bar parks during the audio phase. That is the reporting half of "frozen at ~80%" — this PR fixes the cost, not the reporting. Generated by Claude Code |
Two CI failures on the merged head, neither of them about the audio path. `nix-check.yml` compares nix/package.nix's npmDepsHash against the lockfile and runs on any PR touching `nix/**`. main's recorded hash is stale — it still names the set from before the last few lockfile moves — so merging main in made this branch inherit a failure that belongs to main. The value here is the one the check itself printed. The rest is biome reflowing one call in the new test.
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Update on the two things that were open. All 18 checks are green on Two failures on the way there, neither about the audio path. Biome reflowed one call in the new test. And The nix derivation is still unverified, and not for a reason this PR can fix. I dispatched What that leaves unchecked is narrow, and unchanged from my last comment: that nixpkgs' ffmpeg Note for whoever merges: main requires linear history, so this goes in squashed or rebased, not as a merge commit. Generated by Claude Code |
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Approving. The three blockers from the 27/08 review are addressed and measured, and the 18 checks are green — including the Linux and macOS compositor test jobs, which is where the new atempo assertions actually run against a different ffmpeg than the one I measured on.
Merging with the nix derivation unverified, deliberately and on the record: nix build is currently broken repo-wide (crates.io 403s every crate tarball to the runner, main included), so no signal is obtainable for it today. What that leaves open is narrow — that nixpkgs' ffmpeg .lib output ships libavfilter.so.*, and that the *.so.*.* filter leaves exactly one libavfilter.so.<major>. The glob drift itself, which is the mistake that actually happened, is now locked down by a test.
Thanks @superkc2026 — the atempo swap was the right call, and the factor chaining held up under every speed the editor can produce.
Generated by Claude Code
… bound `speed` is `source_samples / target_samples`, not the speed anyone clicked. A corrupt scene where a handful of samples targets an hour-long span gives an arbitrarily small ratio, and chaining by 0.5 stacked about thirty stages for it — over a thousand for a subnormal — each with its own analysis window and priming loss. The `speed <= 0.0` / non-finite guard caught NaN and zero, not this. `atempo_factors` now returns `None` past eight stages, which reaches 0.5^8 ~= 0.0039, twenty-five times below MIN_PLAYBACK_SPEED. Past that the WSOLA path takes over; it has no bounds to exceed. The upper branch is chained through the same counter — MAX_PLAYBACK_SPEED is 100 so one stage covers everything the editor produces, but a ratio of quantized lengths is not the clicked speed and nothing pins it under the filter's own bound.
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Re-approving on 3d90e8d. 18/18 checks green, every review thread resolved, and the last open one — the unbounded atempo chain on the low end — is capped at eight stages with the WSOLA path taking anything below.
Merging with the nix derivation unverified, on the record: nix build is broken repo-wide right now (crates.io returns 403 to the runner for every crate tarball, main included), so no signal is obtainable for it today. What stays unchecked is narrow — that nixpkgs' ffmpeg .lib output ships libavfilter.so.*, and that the *.so.*.* filter leaves exactly one libavfilter.so.<major>.
Thanks @superkc2026 — the atempo swap was the right call, and the factor chaining held up under every speed the editor can produce.
Generated by Claude Code
… libs, guard --sdk-only - before-pack.cjs macOS: split the combined av* regex (atLeast: 4) into one requirement per library — avcodec/avformat/avutil/swresample/swscale/avfilter — matching the LINUX_REQUIRED style so duplicate versions of one library cannot satisfy the count while another is missing. - before-pack.cjs Windows: add swresample/swscale to the required DLL list (was: avcodec/avformat/avutil/avfilter). - build-and-packaging.md: document all six dylib families in the macOS guard table. - fetch-ffmpeg.mjs: create binDir before readdirSync in fetchSharedDlls, so the --sdk-only path no longer throws on a fresh checkout (binDir is normally created by the CLI branch before the shared-DLL fetch).
…ak it `nix build .#openscreen` has failed for everyone since 2026-08-30. It never reached a derivation of ours: `cargo-vendor-dir` died fetching every crate in the lockfile from `https://crates.io/api/v1/crates/<name>/<version>/download`, which crates.io now answers with 403 — it rate-limits that endpoint to one request per second and points clients at the CDN instead (rust-lang/crates.io#13482). Forty-seven crates, forty-seven 403s, and the same death on `Nix build` runs 33325132923 and 33325656407 on main. nixpkgs fixed it in `importCargoLock` by switching to `https://static.crates.io/crates`. The pin here was from 2026-04-09 and predated that, so this rolls it to d2f6794 (2026-08-29) and says in `flake.nix` why it must not roll back. Verified by building it: `nix build .#openscreen` succeeds. The addon is worth naming, because #371 had to merge with it unverified for exactly this reason — `libavfilter.so.12` is staged beside `compositor_view.node`, exactly one `libavfilter.so.<major>`, `osff_avfilter_graph_alloc@@LIBAVFILTER_12` and friends defined there and nowhere else, no un-renamed `avfilter_*` leaking, ldd fully resolved, and `require()` returns the addon's exports. That is the failure mode the #371 review feared, and it does not happen. `nix-build.yml` now also runs on pull requests touching flake.*, nix/, crates/ or package-lock.json. It is the only job that builds the derivation at all — `nix-check.yml` compares npmDepsHash and nothing else — so a PR rewriting the addon's source filter, its RPATH handling or its symbols.map went green on ~18 checks without one of them building it, and the first real signal arrived on main half an hour after the merge. Path-filtered because the job takes half an hour, and cancel-in-progress on PRs only, so a re-push does not queue a second one while keeping main's runs to completion.
… phase Two separate defects behind "exports frozen at ~80%", neither of them the audio cost that #371 addressed. **The bar could not reach 100%.** The native side reports a raw running count of composed frames and never a total, so the percentage is computed in the renderer — and both callers computed it as `sum(sourceEndSec - sourceStartSec) * fps`, which ignores speed regions. A clip under a 1.25x region emits `duration * fps / 1.25` frames, so the bar climbed to exactly 80% and the export finished there. That is the number in the title, arithmetically. A 0.5x region does the reverse and pins it at 100% for the second half. `outputFrameCount` mirrors `speed_segments_for_window` + `push_speed_segment`, which is what `walk_composited_timeline` actually iterates. The two sides share one fixture table, asserted by `outputFrameCount.test.ts` and by the new `speed_segments_match_the_exporter_frame_totals`, so a change to either goes red instead of drifting. What it cannot mirror is the walk's clamp of each clip to the source's real duration — only a decoder knows that — so a truncated source still reads slightly high, as it did before. **The bar stopped moving.** `on_clip_end` decoded and stretched the clip's audio on the render thread, and nothing calls `progress()` during that, so the bar parked at whatever percentage the clip's last frame reported. A clip's audio depends on nothing but that clip, so it now goes to `ClipAudioJobs` (at most four in flight, results indexed by clip) and the walk carries on to the next clip. The time leaves the export wall rather than being better displayed, and what is left to join at the end is at most the last clip. All three pipelines, not Windows alone — they had the same block character for character. GIF has no audio path and is untouched.
2 participants
Problem
Exports with speed regions appear to freeze at ~80% progress and never finish. Nothing fails — the process just spins at 100% of one core, effectively forever, on long clips.
Root cause
stretch_pcm_to_lengthuses WSOLA, which isO(grain x search_radius)per rendered sample. On a 22-minute clip with a 1.25x speed region, speed-segment quantization produces ~65.4M samples of audio to stretch; the WSOLA pass measured >10 minutes without completing. Audio stretching is the pipeline's last big job, so the progress bar sits at ~80% while it runs, and users kill the export.Fix
Route
stretch_pcm_to_lengththrough an in-process libavfilter graph (abuffer -> atempo -> abuffersink):atempoperforms the same pitch-preserving time-stretch, but is O(n) with ffmpeg's SIMD routines — the same input finishes in seconds.avfilteralready ships in the app:fetch-ffmpeg.mjsvendors everyav*.dllof the BtbN LGPL-shared build and the addon sits beside those DLLs. This PR only links a library that was already in the box — no new dependency, no packaging changes on Windows.build.rs: linkavfilter(bindgen already allowlistsavfilter_*via the existing"av.*"pattern)build-linux-compositor-addon.mjs: stagelibavfilter.so.11alongside the other renamed libs (theosff_symbol-rename table derives from this list); macOS picks dylibs up automaticallyaudio.rs:avfilter_atempo_stretch()mounts the graph, feeds planar f32 chunks, drains, and pads/truncates to the exact target length. Speeds outside atempo's[0.5, 100]window chain multiple stages (e.g. 0.2 ->atempo=0.5,atempo=0.5,atempo=0.8). Any failure returnsNoneand falls back to the existing WSOLA path unchanged.flt(interleaved) orfltp(planar); both are deinterleaved intoPlanarPcmFollow-up commit adds two guards found while diagnosing:
decode_clip_audio: 60s time budget — a truncated/corrupt audio track can keepav_read_framefrom ever returningAVERROR_EOF, spinning the demux loop forever.WsolaTimeStretcher::process: stagnation detection — iffind_best_deltakeeps returning deltas that don't advancegrain_pos, the loop spins forever (only protects the WSOLA fallback now).Testing
cargo test -p openscreen-compositor audio::— 9 tests pass, including new ones: a 10s 440 Hz stereo sine at speed 1.25 returns exactly 8s and measures 440 Hz +/- 2 Hz by zero-crossing count (pitch preserved; a plain resample would shift it), plus length-exactness and multi-stage (out-of-range speed) cases.Notes
Summary by CodeRabbit
New Features
Bug Fixes