michael.di...@xaymar.com:
> From: Michael Fabian 'Xaymar' Dirks <michael.di...@xaymar.com>
>
> Adds "timestamp_precision" to the available options for Matroska muxing.
> The option enables users and developers to change the precision of the
> time stamps in the Matroska 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.di...@xaymar.com>
> ---
> doc/muxers.texi | 8 ++++++++
> libavformat/matroskaenc.c | 33 ++++++++++++++++++++++++++-------
> 2 files changed, 34 insertions(+), 7 deletions(-)
>
> diff --git a/doc/muxers.texi b/doc/muxers.texi
> index e1c6ad0829..8655be94ff 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.
>
> +@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.
This should mention that a too high precision will increase container
overhead.
> +Default is @var{1/1000} (1 millisecond).
> +
> @end table
>
> @anchor{md5}
> diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
> index 186a25d920..1b911a648c 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,
> @@ -1814,6 +1816,7 @@ 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 +1853,10 @@ 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);
There is a serious problem here: mkv->time_base is the time base that
the muxer uses; yet if mkv->time_base is not a multiple of 1/1000000000,
then av_rescale_q will have to round a bit and then the demuxer will
read a different time base, leading to a drift of all timestamps. This
is not acceptable.
> +
> 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 +1889,11 @@ 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 +1954,12 @@ 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);
There are three places where you rescale this; it would be better if you
did it unconditionally in one place (namely after this block here).
> if (mkv->cluster_size_limit < 0)
> mkv->cluster_size_limit = 32 * 1024;
> }
> @@ -2713,6 +2719,14 @@ static int mkv_init(struct AVFormatContext *s)
> } else
> mkv->mode = MODE_MATROSKAv2;
>
> + // WebM requires a timestamp precision of 1ms.
> + if (mkv->mode == MODE_WEBM) {
> + if (av_cmp_q(mkv->time_base, (AVRational){1, 1000}) != 0) {
> + av_log(s, AV_LOG_ERROR, "WebM requires 1ms timestamp
> precision\n");
> + return AVERROR(EINVAL);
> + }
(This could be put into the same block as the one just above that sets
the mode.)
> + }
> +
> mkv->cur_audio_pkt = av_packet_alloc();
> if (!mkv->cur_audio_pkt)
> return AVERROR(ENOMEM);
> @@ -2738,8 +2752,8 @@ 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 +2773,10 @@ 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 +2844,7 @@ 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, INT_MAX, FLAGS},
Using a default value that is a valid value makes it impossible to
distinguish whether the user set a value at all; but I'd like to
preserve that possibility.
> { NULL },
> };
>
>
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