[FFmpeg-devel] [PATCH] avformat/movenc: Explicitly address potential division by zero.

[Lucas Cooper]

I realized that I missed the indentation. I've fixed it in the latest
patch.

On 27 April 2017 at 09:52, Lucas Cooper <bobobo at google.com> wrote:

> find_fps attempts to infer framerate from AVCodec's timebase. When this
> results in a frame rate that isn't explicitly marked as supported in
> av_timecode_check_frame_rate, find_fps returns the AVStream's
> avg_frame_rate, which, per avformat.h, _may_ be set (or not).
>
> mov_get_mpeg2_xdcam_codec_tag, mov_get_h264_codec_tag and
> find_compressor attempt to call av_q2d on the return value of find_fps,
> which in the above case, may result in division by zero and therefore,
> an undefined frame rate when NaN is converted to int.
> ---
>  libavformat/movenc.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
> index e6e2313c53..a5c6ab88f1 100644
> --- a/libavformat/movenc.c
> +++ b/libavformat/movenc.c
> @@ -1321,12 +1321,21 @@ static AVRational find_fps(AVFormatContext *s,
> AVStream *st)
>      return rate;
>  }
>
> +static int defined_frame_rate(AVFormatContext *s, AVStream *st)
> +{
> +    AVRational rational_framerate = find_fps(s, st);
> +    int rate = 0;
> +    if (rational_framerate.den != 0)
> +      rate = av_q2d(rational_framerate);
> +    return rate;
> +}
> +
>  static int mov_get_mpeg2_xdcam_codec_tag(AVFormatContext *s, MOVTrack
> *track)
>  {
>      int tag = track->par->codec_tag;
>      int interlaced = track->par->field_order > AV_FIELD_PROGRESSIVE;
>      AVStream *st = track->st;
> -    int rate = av_q2d(find_fps(s, st));
> +    int rate = defined_frame_rate(s, st);
>
>      if (!tag)
>          tag = MKTAG('m', '2', 'v', '1'); //fallback tag
> @@ -1388,7 +1397,7 @@ static int mov_get_h264_codec_tag(AVFormatContext
> *s, MOVTrack *track)
>      int tag = track->par->codec_tag;
>      int interlaced = track->par->field_order > AV_FIELD_PROGRESSIVE;
>      AVStream *st = track->st;
> -    int rate = av_q2d(find_fps(s, st));
> +    int rate = defined_frame_rate(s, st);
>
>      if (!tag)
>          tag = MKTAG('a', 'v', 'c', 'i'); //fallback tag
> @@ -1850,7 +1859,7 @@ static void find_compressor(char * compressor_name,
> int len, MOVTrack *track)
>      } else if (track->par->codec_id == AV_CODEC_ID_MPEG2VIDEO &&
> xdcam_res) {
>          int interlaced = track->par->field_order > AV_FIELD_PROGRESSIVE;
>          AVStream *st = track->st;
> -        int rate = av_q2d(find_fps(NULL, st));
> +        int rate = defined_frame_rate(NULL, st);
>          av_strlcatf(compressor_name, len, "XDCAM");
>          if (track->par->format == AV_PIX_FMT_YUV422P) {
>              av_strlcatf(compressor_name, len, " HD422");
> --
> 2.13.0.rc0.306.g87b477812d-goog
>
>