[FFmpeg-devel] [PATCH] avfilter/f_realtime: add option to scale speed

[Nicolas George]

Moritz Barsnick (2018-12-25):
> Signed-off-by: Moritz Barsnick <barsnick at gmx.net>
> ---
> This adds two double precision divisions per frame, which seems acceptable.
> 
> I'm not sure scaling the limit by the factor is the correct idea.  It feels
> right regarding the discontinuities, but not according to the limit option's
> description.

I think it would be more logical to keep limit expressed as real time.
This option is a safety net, it is not nimble enough to select time gaps
to ignore in files that contain them.

> 
> 
>  doc/filters.texi         | 4 ++++
>  libavfilter/f_realtime.c | 7 +++++--
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/doc/filters.texi b/doc/filters.texi
> index 65ce25bc18..60ebf2aa99 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -20829,6 +20829,10 @@ They accept the following options:
>  @item limit
>  Time limit for the pauses. Any pause longer than that will be considered
>  a timestamp discontinuity and reset the timer. Default is 2 seconds.
> + at item speed
> +Speed factor for processing. The value must be a float larger than zero.
> +Values larger than 1.0 will speed up processing, smaller will slow it down.
> +The @var{limit} is automatically adapted accordingly. Default is 1.0.
>  @end table
>  
>  @anchor{select}
> diff --git a/libavfilter/f_realtime.c b/libavfilter/f_realtime.c
> index 171c16aaaa..8d4fbf642b 100644
> --- a/libavfilter/f_realtime.c
> +++ b/libavfilter/f_realtime.c
> @@ -22,11 +22,13 @@
>  #include "libavutil/time.h"
>  #include "avfilter.h"
>  #include "internal.h"
> +#include <float.h>
>  
>  typedef struct RealtimeContext {
>      const AVClass *class;
>      int64_t delta;
>      int64_t limit;
> +    double speed;
>      unsigned inited;
>  } RealtimeContext;
>  
> @@ -36,7 +38,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
>      RealtimeContext *s = ctx->priv;
>  
>      if (frame->pts != AV_NOPTS_VALUE) {
> -        int64_t pts = av_rescale_q(frame->pts, inlink->time_base, AV_TIME_BASE_Q);
> +        int64_t pts = av_rescale_q(frame->pts, inlink->time_base, AV_TIME_BASE_Q) / s->speed;
>          int64_t now = av_gettime_relative();
>          int64_t sleep = pts - now + s->delta;
>          if (!s->inited) {
> @@ -44,7 +46,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
>              sleep = 0;
>              s->delta = now - pts;
>          }
> -        if (sleep > s->limit || sleep < -s->limit) {

> +        if (sleep > s->limit / s->speed || sleep < -s->limit / s->speed) {

I should have used FFABS(sleep); if this hunk stays, then better make
the change to have only one division:

	if (FFABS(sleep) > s->limit / s->speed)

>              av_log(ctx, AV_LOG_WARNING,
>                     "time discontinuity detected: %"PRIi64" us, resetting\n",
>                     sleep);
> @@ -65,6 +67,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
>  #define FLAGS AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_FILTERING_PARAM
>  static const AVOption options[] = {
>      { "limit", "sleep time limit", OFFSET(limit), AV_OPT_TYPE_DURATION, { .i64 = 2000000 }, 0, INT64_MAX, FLAGS },
> +    { "speed", "speed factor", OFFSET(speed), AV_OPT_TYPE_DOUBLE, { .dbl = 1.0 }, DBL_MIN, DBL_MAX, FLAGS },
>      { NULL }
>  };
>  

LGTM apart from these nitpicks.

Regards,

-- 
  Nicolas George