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marshiyar
0498cfc075
When a candidate page failed its CRC, `open` had already read and hashed the whole page without charging `recovery_budget`, so the work spent on dense fake capture patterns exceeded the budget that bounds resynchronisation. The page length is now charged, and the scan stops once the budget is spent. The AVI part is already fixed on main; the Matroska part lives in storytold/craft-libs (crates/media/src/matroska/demux.rs), not in this repo. Tested with a counting ByteSource over a file of repeated fake `OggS` headers: total bytes read stay within the budget plus one page (they exceeded it before). Ogg part of #2794; the Matroska part needs a craft-libs change.
filmcraft-ogg
A clean-room Ogg demuxer. Layer L0: no dependencies beyond std, no unsafe, builds for
wasm32-unknown-unknown. No libogg / libopusfile / FFmpeg code was consulted; FFmpeg is used only
as an external fixture generator and test oracle.
Specifications
| Document | Used for |
|---|---|
| RFC 3533 (2003) | pages, lacing, packet continuation, CRC-32, logical bitstreams |
| RFC 7845 (2016) | Ogg Opus: OpusHead / OpusTags, granule positions, pre-skip, end trimming (§4) |
| RFC 6716 (2012) §3.1 | Opus TOC byte: packet durations |
| Vorbis I specification (2020-07-04), §4.2.2 and Appendix A | Vorbis identification header, Ogg mapping |
Use
let bytes = std::fs::read("voice.opus")?;
let ogg = filmcraft_ogg::open(&bytes)?;
let s = ogg.stream_of(filmcraft_ogg::Codec::Opus).unwrap();
let head = &ogg.streams[s].headers[0]; // OpusHead
let pre_skip = u16::from_le_bytes([head[10], head[11]]) as u32;
let timing = filmcraft_ogg::OpusTiming::of(&ogg.streams[s], pre_skip);
let k = timing.starts.partition_point(|&x| x <= 48_000) - 1; // packet holding sample 48 000
let packet = ogg.read_packet(&bytes, s, k)?;
- Every page is read and its CRC checked; damaged pages are dropped and the reader resynchronises
on the next
OggS. Packets spanning pages are lists of byte ranges; a continued page whose start was lost drops the fragment. OpusTiming: packet durations from the TOC; positions anchored on the first page's granule (backwards from it), then accumulated forwards, re-anchoring on any granule discontinuity; the final (end-of-stream) page's smaller granule trims the end. Positions are relative to the first sample after the pre-skip (pre-skip samples are negative).
Tests
src/tests.rs writes synthetic pages: timing with pre-skip and end trimming, packets across pages,
a corrupted page (CRC), every truncation and 300 mutations. crates/codecs/tests/it/ogg_oracle.rs
compares with FFmpeg's libopus / Vorbis decodes (exact length; SNR ≥ 50 dB CELT, ≥ 10 dB SILK,
Vorbis 139 dB) and checks random seeks against the continuous decode.