[FFmpeg-devel] [PATCH 1/2] avfilter/vf_fps: add way to get CFR output without knowing input frame rate

[Gyan]

On 29-10-2019 07:17 PM, Paul B Mahol wrote:
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
>   doc/filters.texi     |  3 +++
>   libavfilter/vf_fps.c | 10 +++++++++-
>   2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/doc/filters.texi b/doc/filters.texi
> index 11f715319a..1e815bf940 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -10737,6 +10737,9 @@ Pass through last frame if input duration has not been reached yet.
>   @end table
>   The default is @code{round}.
>   
> + at item input
> +Pick output frame rate from input if it is available. The default is disabled.
> +Useful to change input to constant frame rate without needing to know input frame rate.
>   @end table
>   
>   Alternatively, the options can be specified as a flat string:
> diff --git a/libavfilter/vf_fps.c b/libavfilter/vf_fps.c
> index cf1e36726a..3561332f0e 100644
> --- a/libavfilter/vf_fps.c
> +++ b/libavfilter/vf_fps.c
> @@ -70,6 +70,7 @@ typedef struct FPSContext {
>       int frames_out;            ///< number of frames on output
>       int dup;                   ///< number of frames duplicated
>       int drop;                  ///< number of framed dropped
> +    int input;                 ///< should filter use input framerate if one is set
>   } FPSContext;
>   
>   #define OFFSET(x) offsetof(FPSContext, x)
> @@ -87,6 +88,7 @@ static const AVOption fps_options[] = {
>       { "eof_action", "action performed for last frame", OFFSET(eof_action), AV_OPT_TYPE_INT, { .i64 = EOF_ACTION_ROUND }, 0, EOF_ACTION_NB-1, V|F, "eof_action" },
>           { "round", "round similar to other frames",  0, AV_OPT_TYPE_CONST, { .i64 = EOF_ACTION_ROUND }, 0, 0, V|F, "eof_action" },
>           { "pass",  "pass through last frame",        0, AV_OPT_TYPE_CONST, { .i64 = EOF_ACTION_PASS  }, 0, 0, V|F, "eof_action" },
> +    { "input", "use input framerate is available", OFFSET(input), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, V|F },
>       { NULL }
>   };
>   
> @@ -99,7 +101,8 @@ static av_cold int init(AVFilterContext *ctx)
>       s->status_pts   = AV_NOPTS_VALUE;
>       s->next_pts     = AV_NOPTS_VALUE;
>   
> -    av_log(ctx, AV_LOG_VERBOSE, "fps=%d/%d\n", s->framerate.num, s->framerate.den);
> +    if (!s->input)
> +        av_log(ctx, AV_LOG_VERBOSE, "fps=%d/%d\n", s->framerate.num, s->framerate.den);
>       return 0;
>   }
>   
> @@ -153,8 +156,13 @@ static int config_props(AVFilterLink* outlink)
>       AVFilterLink    *inlink = ctx->inputs[0];
>       FPSContext      *s      = ctx->priv;
>   
> +    if (s->input && inlink->frame_rate.num > 0 && inlink->frame_rate.den > 0) {
> +        outlink->time_base  = av_inv_q(inlink->frame_rate);
> +        outlink->frame_rate = inlink->frame_rate;

Maybe add some sanity checks for very high frame rates e.g. some WebMs 
whose video fps is detected as 1000.

> +    } else {
>       outlink->time_base  = av_inv_q(s->framerate);
>       outlink->frame_rate = s->framerate;
> +    }
>   
>       /* Calculate the input and output pts offsets for start_time */
>       if (s->start_time != DBL_MAX && s->start_time != AV_NOPTS_VALUE) {

Gyan