[FFmpeg-devel] Exposing preroll and remainder info for aac and mp3.

Dale Curtis dalecurtis at chromium.org
Wed Jul 4 02:30:34 CEST 2012

Hi all,

We're running into problems with leading and trailing silence due to
pre-roll and remainder with aac and mp3 encodes. To illustrate here's a
demo showing the decoded output of a couple mp3 and aac files:


(requires Chrome or very recent Safari). Compare the aac and mp3 results
with ogg.

We're wondering what the best approach is here. Should ffmpeg/libav be
cutting the codec specific preroll information before sending it on? Or
should we simply expose this information through say
AVCodecContext->metadata for downstream consumers to do what they wish with?

See the following for the AAC specific information:

The reason this is necessary is for sample accurate playback of clips which
is important for applications like WebAudio.

Has anyone looked into this before?

Thanks in advance!

- dale

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