[FFmpeg-devel] [PATCH] avfilter/src_movie: fix how we check for overflows with seek_point

Michael Niedermayer michael at niedermayer.cc
Sun Apr 3 01:47:56 CEST 2016

On Sat, Apr 02, 2016 at 09:11:44PM +0300, Marios Titas wrote:
> Currently, if the movie source filter is used and a seek_point is
> specified on a file that has a negative start time, ffmpeg will fail.

> An easy way to reproduce this is as follows:
> $ ffmpeg -vsync passthrough -filter_complex 'color=d=10,setpts=PTS-1/TB' test.mp4
> $ ffmpeg -filter_complex 'movie=filename=test.mp4:seek_point=2' -f null -

can you add a fate test ?

> The problem is caused by checking for int64_t overflow the wrong way.
> In general, to check whether a + b overflows, it is not enough to do:
>     a > INT64_MAX - b
> because b might be negative; the correct way is:
>     b > 0 && > a > INT64_MAX - b
> ---
>  libavfilter/src_movie.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)


note, if one is pedantic then the timestamp > 0 check is unneeed or
if one assumes te surrounding code can be changed to produce < 0
then a underflow check is missing

just saying in case someone wants to fix that pedantic issue


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