[Ffmpeg-devel] [Ffmpeg-devel-old] Division by 0 in av_frac_add()

Nico Sabbi nsabbi
Mon Oct 3 22:57:58 CEST 2005

av_frad_add() doesn't check that f->den != 0; this leads to SIGFPE.

debugging a part of mencoder that recently crashes, and comparing it 
with the last
working revision, I discovered what follows:


AVCodecContext *ctx;
ctx->width = stream->bih->biWidth;
ctx->height = stream->bih->biHeight;

when ctx->width = ctx->height = 0 (non-sense but unfortunately true)
and soon after calling av_write_header() mencoder dies with SIGFPE because
av_frac_add() assigns:

f->val += num / den; with den==0.

The same code in mencoder, although buggy, worked without problems in 


    if(!den) return;

on top av_frac_add() fixes the code; I don't know if it's the right 
solution, but preventing
an invalid operation sounds reasonable in any case.


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