[FFmpeg-devel] [PATCH] Fix to prevent runaway ac3 detection

Marijn Meijles marijn at bitpit.net
Sat Jan 28 14:52:29 EET 2017


This is a fix for https://trac.ffmpeg.org/ticket/6106 .

The issue is that when detecting a swapped AC3 marker the data of the
frame is swapped. However, in subsequent frames the data swapped is
taken from the first frame rather than the current frame. So all frames
are considered to be correct even though they might not be. This
leads to a high probe score and eventual misidentification.

We run a service identifying millions of different wav files and 
apparently the chance of one 'correct' AC3 header in pcm data is big
enough to hit this. But the chance of subsequent frames to be 'correct'
is a lot smaller.

I tested this with AC3 and EAC3 files from your samples repo and with
some of our previously misidentified pcm wav files.


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