[FFmpeg-devel] [PATCH] ffmpeg_filter: switch sub2video.end_pts initialization value to 0

[Jan Ekström]

On Fri, Feb 22, 2019 at 9:56 PM Jan Ekström <jeebjp at gmail.com> wrote:
>
> This seems to fix use cases where the sub2video output is the only
> input to a filter chain.
>
> Additionally, this is the value to which the structure's values
> would implicitly get initialized to. The ballooning buffering case
> would not get hit by this as the value of end_pts after
> (re-)initialization would be less than INT64_MAX, thus hitting the
> sub2video AVFrame initialization logic via sub2video_update in
> sub2video_heartbeat.
> ---
>  fftools/ffmpeg_filter.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fftools/ffmpeg_filter.c b/fftools/ffmpeg_filter.c
> index 72838de1e2..536f9c9c46 100644
> --- a/fftools/ffmpeg_filter.c
> +++ b/fftools/ffmpeg_filter.c
> @@ -739,7 +739,7 @@ static int sub2video_prepare(InputStream *ist, InputFilter *ifilter)
>      if (!ist->sub2video.frame)
>          return AVERROR(ENOMEM);
>      ist->sub2video.last_pts = INT64_MIN;
> -    ist->sub2video.end_pts  = INT64_MIN;
> +    ist->sub2video.end_pts  = 0;
>      return 0;
>  }
>
> --
> 2.20.1
>

An alternative for this would be to:
1. add a flag to sub2video structure that timestamp initialization is
required, and set it as required during (re-)initializations.
2. pass heartbeat pts to sub2video_update
3. finally, in sub2video_update
    } else {
        pts       = !ist->sub2video.timestamp_initialized ?
heartbeat_pts : ist->sub2video.end_pts;
        end_pts   = INT64_MAX;
        num_rects = 0;
    }
   and ist->sub2video.timestamp_initialized = 1; at the end.

This way the sub2video logic would start with the first heartbeat's
timestamp (often zero, but not always), as opposed to the initial
value of end_pts.

Jan