[FFmpeg-devel] [PATCH] avformat/mp3dec: improve junk skipping heuristic

Michael Niedermayer michael at niedermayer.cc
Tue Oct 20 02:12:00 CEST 2015

On Mon, Oct 19, 2015 at 11:12:03PM +0200, wm4 wrote:
> Commit 2b3e9bbfb529e6bde238aeb511b55ebe461664c8 caused problems for a
> certain API user:
> https://code.google.com/p/chromium/issues/detail?id=537725
> https://code.google.com/p/chromium/issues/detail?id=542032
> The problem seems rather arbitrary, because if there's junk, anything
> can happen. In this case, the imperfect junk skipping just caused it to
> read different junk, from what I can see.
> We can improve the accuracy of junk detection by a lot by checking if 2
> consecutive frames use the same configuration. While in theory it might
> be completely fine for the 1st frame to have a different format than the
> 2nd frame, it's exceedingly unlikely, and I can't think of a legitimate
> use-case.
> This is approximately the same mpg123 does for junk skipping. The
> set of compared header bits is the same as the libavcodec mp3 parser
> uses for similar purposes.
> ---
> Now compares less header bits, as requested.
> ---
>  libavformat/mp3dec.c | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)



Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many things microsoft did are stupid, but not doing something just because
microsoft did it is even more stupid. If everything ms did were stupid they
would be bankrupt already.
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