[FFmpeg-devel] [PATCH] ffmpeg: avoid possible undefined behavior

Ganesh Ajjanagadde gajjanagadde at gmail.com
Fri Oct 9 16:39:27 CEST 2015

On lines 1633,1634 FFABS(pts) is performed. However, if av_stream_get_end_pts
returns AV_NOPTS_VALUE always, pts remains stuck at INT64_MIN, leading
to undefined behavior on FFABS.

One could conceive of a solution using FFNABS. However, such a solution
has to deal with the implementation defined rounding of integer division
with at least one negative operand in ANSI C89. C99 forces truncation to
zero, but I am not sure that all of our platforms compile with full C99
support, and in particular whether we can safely assume a fixed
rounding behavior across all platforms.

This solution is simple, and I doubt changing INT64_MIN to INT64_MIN + 1
has any practical loss - if it is stuck at its initial value, the stream
is messed up anyway.

Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
 ffmpeg.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ffmpeg.c b/ffmpeg.c
index e31a2c6..85cc6e4 100644
--- a/ffmpeg.c
+++ b/ffmpeg.c
@@ -1529,7 +1529,7 @@ static void print_report(int is_last_report, int64_t timer_start, int64_t cur_ti
     AVCodecContext *enc;
     int frame_number, vid, i;
     double bitrate;
-    int64_t pts = INT64_MIN;
+    int64_t pts = INT64_MIN + 1;
     static int64_t last_time = -1;
     static int qp_histogram[52];
     int hours, mins, secs, us;

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