[FFmpeg-devel] [PATCH] avformat/matroskaenc: Allow changing the time stamp precision via option

Michael Fabian 'Xaymar' Dirks michael.dirks at xaymar.com
Thu May 20 20:30:55 EEST 2021


On 2021-05-20 19:18, michael.dirks at xaymar.com wrote:
> From: Michael Fabian 'Xaymar' Dirks <michael.dirks at xaymar.com>
>
> Adds "timestamp_precision" to the available option for Matroska/WebM
> muxing. The option enables users and developers to change the precision
> of the time stamps in the Matroska/WebM container up to 1 nanosecond,
> which can aid with the proper detection of constant and variable rate
> content.
>
> Work-around fix for: 259, 6406, 7927, 8909 and 9124.
>
> Signed-off-by: Michael Fabian 'Xaymar' Dirks <michael.dirks at xaymar.com>
> ---
>   doc/muxers.texi           |  8 ++++++++
>   libavformat/matroskaenc.c | 28 ++++++++++++++++++++--------
>   2 files changed, 28 insertions(+), 8 deletions(-)
>
> diff --git a/doc/muxers.texi b/doc/muxers.texi
> index e1c6ad0829..d9f7badae1 100644
> --- a/doc/muxers.texi
> +++ b/doc/muxers.texi
> @@ -1583,6 +1583,14 @@ bitmap is stored bottom-up. Note that this option does not flip the bitmap
>   which has to be done manually beforehand, e.g. by using the vflip filter.
>   Default is @var{false} and indicates bitmap is stored top down.
>   
> + at item timestamp_precision
> +Sets the timestamp precision up to 1 nanosecond for Matroska/WebM, which can
> +improve detection of constant rate content in demuxers. Note that some poorly
> +implemented demuxers may require a timestamp precision of 1 millisecond, so
> +increasing it past that point may result in playback issues. Higher precision
> +also reduces the maximum possible timestamp significantly.
> +Default is @var{1/1000000000} (1 nanosecond).
> +
>   @end table
>   
>   @anchor{md5}
> diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
> index 186a25d920..bff8c8e7f2 100644
> --- a/libavformat/matroskaenc.c
> +++ b/libavformat/matroskaenc.c
> @@ -20,6 +20,7 @@
>    */
>   
>   #include <stdint.h>
> +#include <float.h>
>   
>   #include "av1.h"
>   #include "avc.h"
> @@ -158,6 +159,8 @@ typedef struct MatroskaMuxContext {
>       int                 default_mode;
>   
>       uint32_t            segment_uid[4];
> +
> +    AVRational          time_base;
>   } MatroskaMuxContext;
>   
>   /** 2 bytes * 7 for EBML IDs, 7 1-byte EBML lengths, 6 1-byte uint,
> @@ -1814,6 +1817,7 @@ static int mkv_write_header(AVFormatContext *s)
>       const AVDictionaryEntry *tag;
>       int ret, i, version = 2;
>       int64_t creation_time;
> +    int64_t time_base = 1;
>   
>       if (mkv->mode != MODE_WEBM ||
>           av_dict_get(s->metadata, "stereo_mode", NULL, 0) ||
> @@ -1850,7 +1854,10 @@ static int mkv_write_header(AVFormatContext *s)
>           return ret;
>       pb = mkv->info.bc;
>   
> -    put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 1000000);
> +    time_base = av_rescale_q(time_base, mkv->time_base, (AVRational){1, 1000000000});
> +    av_log(s, AV_LOG_DEBUG, "TimestampScale is: %" PRId64 " ns\n", time_base);
> +    put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 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)) {
> @@ -1883,11 +1890,11 @@ 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 = av_rescale_q(s->duration, AV_TIME_BASE_Q, mkv->time_base);
>               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 = av_rescale_q(metadata_duration, AV_TIME_BASE_Q, mkv->time_base);
>               put_ebml_float(pb, MATROSKA_ID_DURATION, scaledDuration);
>               av_log(s, AV_LOG_DEBUG, "Write early duration from metadata = %" PRIu64 "\n", scaledDuration);
>           } else if (s->pb->seekable & AVIO_SEEKABLE_NORMAL) {
> @@ -1948,12 +1955,12 @@ static int mkv_write_header(AVFormatContext *s)
>       // after 4k and on a keyframe
>       if (IS_SEEKABLE(pb, mkv)) {
>           if (mkv->cluster_time_limit < 0)
> -            mkv->cluster_time_limit = 5000;
> +            mkv->cluster_time_limit = av_rescale_q(5000, (AVRational){1, 1000}, mkv->time_base);
>           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 = av_rescale_q(1000, (AVRational){1, 1000}, mkv->time_base);
>           if (mkv->cluster_size_limit < 0)
>               mkv->cluster_size_limit = 32 * 1024;
>       }
> @@ -2323,7 +2330,7 @@ static int mkv_write_packet_internal(AVFormatContext *s, const AVPacket *pkt)
>               ret = mkv_end_cluster(s);
>               if (ret < 0)
>                   return ret;
> -            av_log(s, AV_LOG_WARNING, "Starting new cluster due to timestamp\n");
> +            av_log(s, AV_LOG_VERBOSE, "Starting new cluster as timestamp offset exceeds signed 16-bit integer range.\n");
>           }
>       }
>   
> @@ -2738,8 +2745,8 @@ static int mkv_init(struct AVFormatContext *s)
>               track->uid = mkv_get_uid(mkv->tracks, i, &c);
>           }
>   
> -        // ms precision is the de-facto standard timescale for mkv files
> -        avpriv_set_pts_info(st, 64, 1, 1000);
> +        // Use user-defined timescale.
> +        avpriv_set_pts_info(st, 64, mkv->time_base.num, mkv->time_base.den);
>   
>           if (st->codecpar->codec_type == AVMEDIA_TYPE_ATTACHMENT) {
>               if (mkv->mode == MODE_WEBM) {
> @@ -2759,6 +2766,10 @@ static int mkv_init(struct AVFormatContext *s)
>           track->track_num_size = ebml_num_size(track->track_num);
>       }
>   
> +    // Scale the configured cluster_time_limit.
> +    if (mkv->cluster_time_limit >= 0)
> +        mkv->cluster_time_limit = av_rescale_q(mkv->cluster_time_limit, (AVRational){1, 1000}, mkv->time_base);
> +
>       if (mkv->is_dash && nb_tracks != 1)
>           return AVERROR(EINVAL);
>   
> @@ -2826,6 +2837,7 @@ static const AVOption options[] = {
>       { "infer", "For each track type, mark the first track of disposition default as default; if none exists, mark the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER }, 0, 0, FLAGS, "default_mode" },
>       { "infer_no_subs", "For each track type, mark the first track of disposition default as default; for audio and video: if none exists, mark the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER_NO_SUBS }, 0, 0, FLAGS, "default_mode" },
>       { "passthrough", "Use the disposition flag as-is", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_PASSTHROUGH }, 0, 0, FLAGS, "default_mode" },
> +    { "timestamp_precision", "Timestamp precision to use for the entire container", OFFSET(time_base), AV_OPT_TYPE_RATIONAL, { .dbl = 0.000000001 }, 0.000000001, DBL_MAX, FLAGS},
>       { NULL },
>   };

This should have all the requested changes, including the update to documentation. Unfortunately I was not able to get rid of the new cluster spam, so I moved it down a few logging levels into "verbose". While I was at it, I also extended the positive range to an infinitely large number, as I found no valid reason to arbitrarily limit it when the format itself supports and positive unsigned 64-bit integer for the time stamp scale.

This should hopefully be the last change to the patch.

-- 
Sincerely | Mit freundlichen Grüßen

Michael Fabian 'Xaymar' Dirks
Software Designer & Engineer




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