[FFmpeg-devel] [PATCH] avfilter/vf_fps: extend support for expressions

[Gyan Doshi]

On 2021-06-05 21:22, James Almer wrote:
> AV_OPT_TYPE_VIDEO_RATE AVOption types are parsed as expressions, but in a
> limited way. For example, name constants can only be parsed alone and not as
> part of a longer expression.
>
> This change allows usage like
>
> ffmpeg -i IN -vf fps="if(eq(source_fps\,film)\,ntsc_film\,source_fps)" OUT
>
> Suggested-by: ffmpeg at fb.com
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>   libavfilter/vf_fps.c | 65 ++++++++++++++++++++++++++++++++++++++++----
>   1 file changed, 60 insertions(+), 5 deletions(-)
>
> diff --git a/libavfilter/vf_fps.c b/libavfilter/vf_fps.c
> index b7b2d6f2db..29588a5f6e 100644
> --- a/libavfilter/vf_fps.c
> +++ b/libavfilter/vf_fps.c
> @@ -30,6 +30,7 @@
>   #include <stdint.h>
>   
>   #include "libavutil/avassert.h"
> +#include "libavutil/eval.h"
>   #include "libavutil/mathematics.h"
>   #include "libavutil/opt.h"
>   #include "avfilter.h"
> @@ -42,12 +43,47 @@ enum EOFAction {
>       EOF_ACTION_NB
>   };
>   
> +static const char *const var_names[] = {
> +  "source_fps",
> +  "ntsc",
> +  "pal",
> +  "qntsc",
> +  "qpal",
> +  "sntsc",
> +  "spal",
> +  "film",
> +  "ntsc_film",
> +  NULL
> +};
> +
> +enum var_name {
> +  VAR_SOURCE_FPS,
> +  VAR_FPS_NTSC,
> +  VAR_FPS_PAL,
> +  VAR_FPS_QNTSC,
> +  VAR_FPS_QPAL,
> +  VAR_FPS_SNTSC,
> +  VAR_FPS_SPAL,
> +  VAR_FPS_FILM,
> +  VAR_FPS_NTSC_FILM,
> +  VARS_NB
> +};
> +
> +static const double ntsc_fps = 30000.0 / 1001.0;
> +static const double pal_fps = 25.0;
> +static const double qntsc_fps = 30000.0 / 1001.0;
> +static const double qpal_fps = 25.0;
> +static const double sntsc_fps = 30000.0 / 1001.0;
> +static const double spal_fps = 25.0;
> +static const double film_fps = 24.0;
> +static const double ntsc_film_fps = 24000.0 / 1001.0;

Sorry, I missed this before you applied it but what's the q- and s- 
prefixed standards with identical rates?
I can't find any specs or docs online.


> +
>   typedef struct FPSContext {
>       const AVClass *class;
>   
>       double start_time;      ///< pts, in seconds, of the expected first frame
>   
> -    AVRational framerate;   ///< target framerate
> +    char *framerate;        ///< expression that defines the target framerate
>       int rounding;           ///< AVRounding method for timestamps
>       int eof_action;         ///< action performed for last frame in FIFO
>   
> @@ -76,7 +112,7 @@ typedef struct FPSContext {
>   #define V AV_OPT_FLAG_VIDEO_PARAM
>   #define F AV_OPT_FLAG_FILTERING_PARAM
>   static const AVOption fps_options[] = {
> -    { "fps", "A string describing desired output framerate", OFFSET(framerate), AV_OPT_TYPE_VIDEO_RATE, { .str = "25" }, 0, INT_MAX, V|F },
> +    { "fps", "A string describing desired output framerate", OFFSET(framerate), AV_OPT_TYPE_STRING, { .str = "25" }, 0, 0, V|F },
>       { "start_time", "Assume the first PTS should be this value.", OFFSET(start_time), AV_OPT_TYPE_DOUBLE, { .dbl = DBL_MAX}, -DBL_MAX, DBL_MAX, V|F },
>       { "round", "set rounding method for timestamps", OFFSET(rounding), AV_OPT_TYPE_INT, { .i64 = AV_ROUND_NEAR_INF }, 0, 5, V|F, "round" },
>           { "zero", "round towards 0",                 0, AV_OPT_TYPE_CONST, { .i64 = AV_ROUND_ZERO     }, 0, 0, V|F, "round" },
> @@ -99,7 +135,6 @@ 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);
>       return 0;
>   }
>   
> @@ -153,8 +188,26 @@ static int config_props(AVFilterLink* outlink)
>       AVFilterLink    *inlink = ctx->inputs[0];
>       FPSContext      *s      = ctx->priv;
>   
> -    outlink->time_base  = av_inv_q(s->framerate);
> -    outlink->frame_rate = s->framerate;
> +    double var_values[VARS_NB], res;
> +    int ret;
> +
> +    var_values[VAR_SOURCE_FPS]    = av_q2d(inlink->frame_rate);
> +    var_values[VAR_FPS_NTSC]      = ntsc_fps;
> +    var_values[VAR_FPS_PAL]       = pal_fps;
> +    var_values[VAR_FPS_QNTSC]     = qntsc_fps;
> +    var_values[VAR_FPS_QPAL]      = qpal_fps;
> +    var_values[VAR_FPS_SNTSC]     = sntsc_fps;
> +    var_values[VAR_FPS_SPAL]      = spal_fps;
> +    var_values[VAR_FPS_FILM]      = film_fps;
> +    var_values[VAR_FPS_NTSC_FILM] = ntsc_film_fps;
> +    ret = av_expr_parse_and_eval(&res, s->framerate,
> +                                 var_names, var_values,
> +                                 NULL, NULL, NULL, NULL, NULL, 0, ctx);
> +    if (ret < 0)
> +        return ret;
> +
> +    outlink->frame_rate = av_d2q(res, INT_MAX);
> +    outlink->time_base  = av_inv_q(outlink->frame_rate);
>   
>       /* Calculate the input and output pts offsets for start_time */
>       if (s->start_time != DBL_MAX && s->start_time != AV_NOPTS_VALUE) {
> @@ -173,6 +226,8 @@ static int config_props(AVFilterLink* outlink)
>                  s->in_pts_off, s->out_pts_off, s->start_time);
>       }
>   
> +    av_log(ctx, AV_LOG_VERBOSE, "fps=%d/%d\n", outlink->frame_rate.num, outlink->frame_rate.den);
> +
>       return 0;
>   }
>