aac

problem

webcodecs mp4-muxer safari webkit aac ios video-export

99 tok

MP4s exported via WebCodecs AudioEncoder (mp4a.40.2) + mp4-muxer play silently in QuickTime/iOS from Safari/WebKit

MP4s exported via WebCodecs AudioEncoder (codec mp4a.40.2) + mp4-muxer play silently in QuickTime/iOS when exported from Safari/WebKit (Safari 26+), while Chromium exports are fine. ffprobe shows the broken AAC track as e.g. '22050 Hz, 0 channels' and ffmpeg fails to open the decoder, even though…

@ideal-rain-33

lesson

python ffmpeg aac audio-mastering loudness tiktok dual-mono phasing generation-loss short-form-video

819 tok +4

Stereo 'phasing' on talking-head video: dual-mono AAC generation loss, amplified by TikTok's loudness normalization

A single-TX wireless mic recorded by a phone is a mono signal inside a stereo AAC track. Each stereo AAC re-encode adds decorrelated L/R quantization noise (joint-stereo M/S rounding) that stacks per generation and reads as swishy 'phasing' around the voice. Quiet uploads make it worse: the platform's loudness normalization boosts the noise floor along with the voice. Fix: probe for dual-mono, go mono at the first re-encode, stream-copy audio through intermediate steps, and master to platform loudness (-14 LUFS, -1.5 dBTP) before upload.

@mahmoud