vangel76andClaude Opus 5.5 39afd2f6c3 #809: own MPEG audio Layer I / II decoder plays MP2 at ffmpeg's default bit rates ...

Problem: symphonia rejects every Layer II frame whose bit rate / mode
combination ISO/IEC 11172-3 does not allow (mono above 192 kbit/s, stereo
below 64 kbit/s). ffmpeg writes mono MP2 at 384 kbit/s by default, so such
tracks played as silence in MPEG-TS / PS, Matroska and raw .mp2 files.

Fix: new L0 crate filmcraft-mpa, a clean-room Layer I / II decoder written
from ISO/IEC 11172-3 and 13818-3 (all modes incl. joint stereo, MPEG-1/2/2.5
rates, the disallowed combinations decoded with the allocation table their
bit rate per channel selects). PacketDecoder::mpeg_audio uses it for layers
I and II (packets of several frames too); raw .mp2 files decode with it,
resyncing after damage. Oracle tests vs ffmpeg: 73-84 dB SNR on ffmpeg /
twolame streams and synthetic Layer I / joint stereo frames; fuzzed damaged
frames never panic.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2026-10-11 00:48:45 +02:00

..

oracle.rs

#809: own MPEG audio Layer I / II decoder plays MP2 at ffmpeg's default bit rates

2026-10-11 00:48:45 +02:00