[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 21:00:47 EEST 2021
On 2021-05-20 19:26, James Almer wrote:
> On 5/20/2021 2:18 PM, 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).
>
> Like i said, the default must be the one defined in the spec. This version not only would need FATE test updates, it also like you described makes all new files by default have a lot of overhead from having one block per cluster.
I am aware of what you said and I am also aware of Lynne said. I do not know who has the actual final say in this, all I know is that the maintainers for matroskaenc.c are "David Conrad" and "Andreas Rheinhardt" - both of which have not commented on this yet.
>
> I'll apply the previous version later if no one has any comment about the implementation, or the option name (I'd prefer timestamp_scale instead, following the element name).
I chose "timestamp_precision" over "timestamp_scale", as the latter has different meanings when read. "timestamp_precision" directly implies that the option modifies how accurate the time stamps will be, while "timestamp_scale" has no such meaning to readers.
>
>> +
>> @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 },
>> };
>>
--
Sincerely | Mit freundlichen Grüßen
Michael Fabian 'Xaymar' Dirks
Software Designer & Engineer
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