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

[Marios Titas]

ffmpeg | branch: release/2.8 | Marios Titas <redneb at gmx.com> | Sat Apr  2 21:11:44 2016 +0300| [21fb4d1282788abf21f7e9a7b0078be748304179] | committer: Michael Niedermayer

avfilter/src_movie: fix how we check for overflows with seek_point

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 -

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

Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit c1f9734f977f59bc0034096afbe8e43e40d93a5d)

Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=21fb4d1282788abf21f7e9a7b0078be748304179
---

 libavfilter/src_movie.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavfilter/src_movie.c b/libavfilter/src_movie.c
index a7024b9..c006d99 100644
--- a/libavfilter/src_movie.c
+++ b/libavfilter/src_movie.c
@@ -241,7 +241,7 @@ static av_cold int movie_common_init(AVFilterContext *ctx)
         timestamp = movie->seek_point;
         // add the stream start time, should it exist
         if (movie->format_ctx->start_time != AV_NOPTS_VALUE) {
-            if (timestamp > INT64_MAX - movie->format_ctx->start_time) {
+            if (timestamp > 0 && movie->format_ctx->start_time > INT64_MAX - timestamp) {
                 av_log(ctx, AV_LOG_ERROR,
                        "%s: seek value overflow with start_time:%"PRId64" seek_point:%"PRId64"\n",
                        movie->file_name, movie->format_ctx->start_time, movie->seek_point);