[FFmpeg-devel] [PATCH 2/2] avformat/microdvd: export the declared frame rate

[Clément Bœsch]

On Sun, Mar 02, 2014 at 10:36:42PM +0100, wm4 wrote:
> MicroDVD files are normally frame-based (i.e. there are no absolute
> timestamps), but can have an optional frame rate header. If this
> header is missing, the timestamps depend on the frame rate of the
> video they were created for.
> 
> The demuxer will use a fallback frame rate if it's missing from the
> header. Currently, applications using libavformat can't know whether
> the time base is based on the fallback value, or if a frame rate
> header was present.
> 
> This commit introduces a subfps AVOption for MicroDVD, and the
> demuxer sets it if and only if a frame rate header was present.
> ---
>  libavformat/microdvddec.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/libavformat/microdvddec.c b/libavformat/microdvddec.c
> index 42c6de0..a705442 100644
> --- a/libavformat/microdvddec.c
> +++ b/libavformat/microdvddec.c
> @@ -24,12 +24,15 @@
>  #include "internal.h"
>  #include "subtitles.h"
>  #include "libavutil/intreadwrite.h"
> +#include "libavutil/opt.h"
>  
>  #define MAX_LINESIZE 2048
>  
>  
>  typedef struct {
> +    const AVClass *class;
>      FFDemuxSubtitlesQueue q;
> +    AVRational frame_rate;
>  } MicroDVDContext;
>  
>  
> @@ -80,6 +83,7 @@ static int microdvd_read_header(AVFormatContext *s)
>      AVStream *st = avformat_new_stream(s, NULL);
>      int i = 0;
>      char line_buf[MAX_LINESIZE];
> +    int has_real_fps = 0;
>  
>      if (!st)
>          return AVERROR(ENOMEM);
> @@ -105,8 +109,10 @@ static int microdvd_read_header(AVFormatContext *s)
>  
>              if ((sscanf(line, "{%d}{}%6lf",    &frame, &fps) == 2 ||
>                   sscanf(line, "{%d}{%*d}%6lf", &frame, &fps) == 2)
> -                && frame <= 1 && fps > 3 && fps < 100)
> +                && frame <= 1 && fps > 3 && fps < 100) {
>                  pts_info = av_d2q(fps, 100000);
> +                has_real_fps = 1;
> +            }
>              if (!st->codec->extradata && sscanf(line, "{DEFAULT}{}%c", &c) == 1) {
>                  st->codec->extradata = av_strdup(line + 11);
>                  if (!st->codec->extradata)
> @@ -135,6 +141,11 @@ static int microdvd_read_header(AVFormatContext *s)
>          sub->duration = get_duration(line);
>      }
>      ff_subtitles_queue_finalize(&microdvd->q);
> +    if (has_real_fps) {
> +        microdvd->frame_rate = pts_info;
> +    } else if (microdvd->frame_rate.num) {
> +        pts_info = microdvd->frame_rate;
> +    }
>      avpriv_set_pts_info(st, 64, pts_info.den, pts_info.num);
>      st->codec->codec_type = AVMEDIA_TYPE_SUBTITLE;
>      st->codec->codec_id   = AV_CODEC_ID_MICRODVD;
> @@ -162,6 +173,21 @@ static int microdvd_read_close(AVFormatContext *s)
>      return 0;
>  }
>  
> +
> +#define OFFSET(x) offsetof(MicroDVDContext, x)
> +#define SD AV_OPT_FLAG_SUBTITLE_PARAM|AV_OPT_FLAG_DECODING_PARAM
> +static const AVOption microdvd_options[] = {
> +    { "subfps", "set the movie frame rate", OFFSET(frame_rate), AV_OPT_TYPE_RATIONAL, {.dbl=0}, 0, INT_MAX, SD },
> +    { NULL }
> +};
> +
> +static const AVClass microdvd_class = {
> +    .class_name = "microdvddec",
> +    .item_name  = av_default_item_name,
> +    .option     = microdvd_options,
> +    .version    = LIBAVUTIL_VERSION_INT,
> +};
> +
>  AVInputFormat ff_microdvd_demuxer = {
>      .name           = "microdvd",
>      .long_name      = NULL_IF_CONFIG_SMALL("MicroDVD subtitle format"),
> @@ -171,4 +197,5 @@ AVInputFormat ff_microdvd_demuxer = {
>      .read_packet    = microdvd_read_packet,
>      .read_seek2     = microdvd_read_seek,
>      .read_close     = microdvd_read_close,
> +    .priv_class     = &microdvd_class,
>  };

Pushed with 3 changes: lavf micro bumped, added 2 comments, explicit that
the subfps is a fallback.

Thanks,

-- 
Clément B.
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