Problem: footage audio kept only its first two channels, so the centre, LFE and surrounds of a 5.1 file were dropped. AAC 5.1 was worse: FilmCraft's AAC-LC decoder delivers AAC's own order (C L R Ls Rs LFE), so the left output was the centre and front-right was lost.
Fix: crates/media/src/downmix.rs holds one ITU-R BS.775 stereo downmix (centre and surrounds at -3 dB, LFE left out, fixed normalisation by the largest row sum so full scale cannot clip), with channel orders for 3 to 8 channels in WAVE/SMPTE order and AAC's native order, and only the front pair for more than 8. MediaPool::read_stereo applies it, which preview, waveform and export mixdown all read through. Mono and stereo are unchanged.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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