On 1/13/2021 5:50 PM, Thierry Foucu wrote:
a note with this change: If we set the timecodescale to microsecond, and we encode a 30 fps video, the duration of each frame are then 33333 us. In this case, (int16_t)cluster_time != cluster_time Will almost every time faile and we will need to create a new block per frame (it seems to me at least) Because in the block header, there is a timestamp relative to Cluster timestamp (signed int16) which cannot represent 33333On Wed, Jan 13, 2021 at 12:02 PM James Almer <jamr...@gmail.com> wrote:On 1/13/2021 2:46 PM, Thierry Foucu wrote:By default the time code scale in a MKV file in millisecond. With this option we can set the time code scale to microsecond or nanoseconds for very high frame rate. --- libavformat/matroskaenc.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c index 233c472b8f..cfad6a4693 100644 --- a/libavformat/matroskaenc.c +++ b/libavformat/matroskaenc.c @@ -158,6 +158,8 @@ typedef struct MatroskaMuxContext { int default_mode; uint32_t segment_uid[4]; + + int64_t timecodescale; } MatroskaMuxContext; /** 2 bytes * 7 for EBML IDs, 7 1-byte EBML lengths, 6 1-byte uint, @@ -1827,7 +1829,7 @@ static int mkv_write_header(AVFormatContext *s) return ret; pb = mkv->info.bc; - put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 1000000); + put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, mkv->timecodescale); 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)) { @@ -1927,12 +1929,12 @@ 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 = 5*(1000000000/mkv->timecodescale);Either 1000000000LL, or use av_rescale(). Same for the two belowif (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 = 1*(1000000000/mkv->timecodescale); if (mkv->cluster_size_limit < 0) mkv->cluster_size_limit = 32 * 1024; } @@ -2708,7 +2710,7 @@ static int mkv_init(struct AVFormatContext *s) } // ms precision is the de-facto standard timescale for mkvfiles- avpriv_set_pts_info(st, 64, 1, 1000); + avpriv_set_pts_info(st, 64, 1, 1000000000/mkv->timecodescale); if (st->codecpar->codec_type == AVMEDIA_TYPE_ATTACHMENT) { if (mkv->mode == MODE_WEBM) { @@ -2795,6 +2797,7 @@ static const AVOption options[] = { { "infer", "For each track type, mark the first track ofdisposition 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 ofdisposition 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" },+ { "timecodescale", "Time code scale for all tracks in nanoseconds",OFFSET(timecodescale), AV_OPT_TYPE_INT64, { .i64 = 1000000 }, 1, 1000000000, FLAGS },{ NULL }, };Does this cover all cases? A timecodescale of 1000000 was implied until now, so many parts of the code could be hardcoding it in a non obvious way. I see for example MATROSKA_ID_DURATION is set as av_rescale(s->duration, 1000, AV_TIME_BASE). Should that AV_TIME_BASE be changed to mkv->timecodescale? The spec says "Duration of the Segment in nanoseconds based on TimestampScale."Interesting. I did not have to change this because if I check the Metadata DURATION coming from the demuxer with a default ms and set to microsecond, I do see in both: DURATION : 00:00:01.001000000 or is it another duration I need to look at, like this one: https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/matroskaenc.c#L1863
That and the one immediately after it are the ones i was talking about, yes. In any case, it seems to be a temporary value written to the output that will afterwards be overwritten in https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/matroskaenc.c#L2559 when writing the trailer.
The commit that added the code in mkv_write_header() is 70c1647a350. I guess you could ensure the temp value written there is correct by forcing the muxing process to stop without calling mkv_write_trailer(), or commenting out the code writing the final duration value.
See output: # default behavoir ./ffmpeg -f lavfi -i "testsrc=r=30000/1001" -debug_ts -t 1 -y -f matroska /tmp/test.mkv ./ffmpeg -i /tmp/test.mkv ffmpeg version N-100413-g3799e77f93 Copyright (c) 2000-2020 the FFmpeg developers built with gcc 10 (Debian 10.2.0-19) configuration: --disable-optimizations libavutil 56. 62.100 / 56. 62.100 libavcodec 58.115.102 / 58.115.102 libavformat 58. 65.100 / 58. 65.100 libavdevice 58. 11.103 / 58. 11.103 libavfilter 7. 93.100 / 7. 93.100 libswscale 5. 8.100 / 5. 8.100 libswresample 3. 8.100 / 3. 8.100 Input #0, matroska,webm, from '/tmp/test.mkv': Metadata: ENCODER : Lavf58.65.100 Duration: 00:00:01.00, start: 0.000000, bitrate: 412 kb/s Stream #0:0: Video: mpeg4 (Simple Profile), yuv420p(tv, progressive), 320x240 [SAR 1:1 DAR 4:3], 29.97 fps, 29.97 tbr, 1k tbn, 30k tbc (default) Metadata: ENCODER : Lavc58.115.102 mpeg4 DURATION : 00:00:01.001000000 # set the timecodescale to microsecond ./ffmpeg -f lavfi -i "testsrc=r=30000/1001" -debug_ts -t 1 -timecodescale 1000 -y -f matroska /tmp/test_2.mkv ./ffmpeg -i /tmp/test_2.mkv ffmpeg version N-100413-g3799e77f93 Copyright (c) 2000-2020 the FFmpeg developers built with gcc 10 (Debian 10.2.0-19) configuration: --disable-optimizations libavutil 56. 62.100 / 56. 62.100 libavcodec 58.115.102 / 58.115.102 libavformat 58. 65.100 / 58. 65.100 libavdevice 58. 11.103 / 58. 11.103 libavfilter 7. 93.100 / 7. 93.100 libswscale 5. 8.100 / 5. 8.100 libswresample 3. 8.100 / 3. 8.100 Input #0, matroska,webm, from '/tmp/test_2.mkv': Metadata: ENCODER : Lavf58.65.100 Duration: 00:00:01.00, start: 0.000000, bitrate: 416 kb/s Stream #0:0: Video: mpeg4 (Simple Profile), yuv420p(tv, progressive), 320x240 [SAR 1:1 DAR 4:3], 29.97 fps, 29.97 tbr, 1000k tbn, 30k tbc (default) Metadata: ENCODER : Lavc58.115.102 mpeg4 DURATION : 00:00:01.001000000 _______________________________________________ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
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