[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 20:34:00 EEST 2021
On 2021-05-19 17:14, Lynne wrote:
> May 19, 2021, 17:12 by dev at lynne.ee:
>
>> 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.
>> 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.
>>
>> We're bumping to 5.0 next release anyway, and if any users have issues,
>> they can manually set this to 1ms.
>>
> Or better yet, use the timebase to decide the value.
> That way, remuxing Matroska won't break anything, and the overhead
> will be lower.
Most likely 1 ns would already cover any possible situation that could break, if the remote has a proper implementation of the Matroska spec. Calculating the time scale based on the time base of every stream is possible, but I'm fairly sure it would involve semi-complex code.
--
Sincerely | Mit freundlichen Grüßen
Michael Fabian 'Xaymar' Dirks
Software Designer & Engineer
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