[FFmpeg-devel] [PATCH] avformat/matroskaenc: Increase time stamp precision to AV_TIME_BASE

[Michael Fabian 'Xaymar' Dirks]

On 2021-05-19 01:47, michael.dirks at xaymar.com wrote:
> From: Michael Fabian 'Xaymar' Dirks <info at xaymar.com>
>
> Increases the time stamp precision to 1 microsecond, the same as
> AV_TIME_BASE. This hopefully prevents demuxers from being confused on
> the number of frames/samples we actually have per second, and should
> mark all future Matroska/WebM content as being constant rate.
>
> Work-around for: 259, 6406, 7927, 8909, 9124.
>
> Signed-off-by: Michael Fabian 'Xaymar' Dirks <info at xaymar.com>
> ---
>   libavformat/matroskaenc.c | 19 ++++++++++++-------
>   1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
> index ad7b0bf2c6..474e44485a 100644
> --- a/libavformat/matroskaenc.c
> +++ b/libavformat/matroskaenc.c
> @@ -1917,7 +1917,8 @@ static int mkv_write_header(AVFormatContext *s)
>           return ret;
>       pb = mkv->info_bc;
>   
> -    put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 1000000);
> +    // Set time base to 1 microsecond.
> +    put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 1000000000 / AV_TIME_BASE);
>       if ((tag = av_dict_get(s->metadata, "title", NULL, 0)))
>           put_ebml_string(pb, MATROSKA_ID_TITLE, tag->value);
>       if (!(s->flags & AVFMT_FLAG_BITEXACT)) {
> @@ -1959,11 +1960,11 @@ static int mkv_write_header(AVFormatContext *s)
>           int64_t metadata_duration = get_metadata_duration(s);
>   
>           if (s->duration > 0) {
> -            int64_t scaledDuration = av_rescale(s->duration, 1000, AV_TIME_BASE);
> +            int64_t scaledDuration = s->duration;
>               put_ebml_float(pb, MATROSKA_ID_DURATION, scaledDuration);
>               av_log(s, AV_LOG_DEBUG, "Write early duration from recording time = %" PRIu64 "\n", scaledDuration);
>           } else if (metadata_duration > 0) {
> -            int64_t scaledDuration = av_rescale(metadata_duration, 1000, AV_TIME_BASE);
> +            int64_t scaledDuration = metadata_duration;
>               put_ebml_float(pb, MATROSKA_ID_DURATION, scaledDuration);
>               av_log(s, AV_LOG_DEBUG, "Write early duration from metadata = %" PRIu64 "\n", scaledDuration);
>           } else {
> @@ -2038,12 +2039,12 @@ static int mkv_write_header(AVFormatContext *s)
>       // after 4k and on a keyframe
>       if (pb->seekable & AVIO_SEEKABLE_NORMAL) {
>           if (mkv->cluster_time_limit < 0)
> -            mkv->cluster_time_limit = 5000;
> +            mkv->cluster_time_limit = 5000000;
>           if (mkv->cluster_size_limit < 0)
>               mkv->cluster_size_limit = 5 * 1024 * 1024;
>       } else {
>           if (mkv->cluster_time_limit < 0)
> -            mkv->cluster_time_limit = 1000;
> +            mkv->cluster_time_limit = 1000000;
>           if (mkv->cluster_size_limit < 0)
>               mkv->cluster_size_limit = 32 * 1024;
>       }
> @@ -2724,6 +2725,7 @@ static int webm_query_codec(enum AVCodecID codec_id, int std_compliance)
>   static int mkv_init(struct AVFormatContext *s)
>   {
>       int i;
> +    MatroskaMuxContext *mkv = s->priv_data;
>   
>       if (s->nb_streams > MAX_TRACKS) {
>           av_log(s, AV_LOG_ERROR,
> @@ -2752,10 +2754,13 @@ static int mkv_init(struct AVFormatContext *s)
>       }
>   
>       for (i = 0; i < s->nb_streams; i++) {
> -        // ms precision is the de-facto standard timescale for mkv files
> -        avpriv_set_pts_info(s->streams[i], 64, 1, 1000);
> +        // Use µs precision (same as FFmpeg)
> +        avpriv_set_pts_info(s->streams[i], 64, 1, AV_TIME_BASE);
>       }
>   
> +    // Scale the configured cluster_time_limit to microseconds.
> +    mkv->cluster_time_limit = av_rescale(mkv->cluster_time_limit, 1000, AV_TIME_BASE);
> +
>       return 0;
>   }
>   

This is the patch for release/4.2, I should have added that to the commit message.

-- 
Sincerely | Mit freundlichen Grüßen

Michael Fabian 'Xaymar' Dirks
Software Designer & Engineer