[FFmpeg-devel] [PATCH] avformat/matroskaenc: Allow customizing the time stamp precision via option
Michael Fabian 'Xaymar' Dirks
michael.dirks at xaymar.com
Wed May 19 20:25:18 EEST 2021
On 2021-05-19 17:12, Lynne wrote:
> May 19, 2021, 03:44 by michael.dirks at xaymar.com:
>
>> From: Michael Fabian 'Xaymar' Dirks <michael.dirks at xaymar.com>
>>
>> Adds the "timestamp_precision" option to matroskaenc, which allows users
>> to increase the time stamp precision up to 1 nanosecond. This aids with
>> certain demuxers being unable to detect constant rate. It is a work
>> around fix for the problems reported in 259, 6406, 7927, 8909 and 9124.
>>
>> Signed-off-by: Michael Fabian 'Xaymar' Dirks <michael.dirks at xaymar.com>
>> ---
>> libavformat/matroskaenc.c | 25 ++++++++++++++++++-------
>> 1 file changed, 18 insertions(+), 7 deletions(-)
>>
>> diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
>> index b4284a8778..8e2813c36e 100644
>> --- a/libavformat/matroskaenc.c
>> +++ b/libavformat/matroskaenc.c
>> @@ -158,6 +158,8 @@ 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,
>> @@ -1816,6 +1818,7 @@ 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) ||
>> @@ -1852,7 +1855,10 @@ 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)) {
>> @@ -1885,11 +1891,11 @@ 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) {
>> @@ -1950,12 +1956,12 @@ 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;
>> }
>> @@ -2736,8 +2742,8 @@ 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) {
>> @@ -2757,6 +2763,10 @@ 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);
>>
>> @@ -2824,6 +2834,7 @@ 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 = 0.001 }, 0.000000001, 1.0, FLAGS},
>> { NULL },
>> };
>>
> Make the default 1 ns.
In the original patch submission it was requested to be 1 ms for compatibility reasons. The main problem with 1 ns is that we only have a 16-bit signed integer to work with when offsetting the timestamp within a cluster. There is no way to represent anything higher than 32767 ns, so every new frame is a new cluster for any stream.
> This is 2021. I'm not accepting any compromises. Matroska has
> dragged its heels for long enough, video players have resorted to hacks
> to fix time stamps, and high-framerate video is still unacceptably jittery.
If you have any input, the best way to make it heard would be via the standardization process. There are proposed changes to support per-track time bases in the IETF repository for Matroska/WebM video:
- https://github.com/ietf-wg-cellar/matroska-specification/pull/425
- https://github.com/ietf-wg-cellar/matroska-specification/pull/437
At least one of those would permanently solve the issue, with the other being a work-around for the issue.
--
Sincerely | Mit freundlichen Grüßen
Michael Fabian 'Xaymar' Dirks
Software Designer & Engineer
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