On 2021-03-19 03:22, Jan Ekström wrote:
On Thu, Mar 18, 2021 at 5:07 PM Jan Ekström <jee...@gmail.com> wrote:
On Thu, Mar 18, 2021, 17:01 Gyan Doshi <ffm...@gyani.pro> wrote:
On 2021-03-18 20:12, Jan Ekström wrote:
So right now we do have an option in ffmpeg.c called itsoffset. It
lets you configure the input offset in time (seconds - such as
"1337.123" or time format - such as "00:00:01.123"). The only problem
with it right now is that unless you set -copyts it will not get
applied for anything else than subtitles, as the offset gets applied
before and is not taken into account in the "start from PTS 0"
calculation for video/audio streams.
Not the case.
ffmpeg -f lavfi -itsoffset 3 -i nullsrc=r=1:d=3 -vf showinfo -f null -
gives
[Parsed_showinfo_0 @ 0000019cc1b88540] n: 0 pts: 3 pts_time:3 ...
[Parsed_showinfo_0 @ 0000019cc1b88540] n: 1 pts: 4 pts_time:4 ...
[Parsed_showinfo_0 @ 0000019cc1b88540] n: 2 pts: 5 pts_time:5 ...
I've used it many times to adjust sync among streams.
Regards,
Gyan
Very interesting!
I will have to retest, I just recall that the last time I tried it got applied
when there were multiple streams in an input when the start_time based
adjustment was done.
Right, so taking in a Matroska file it works fine, but when taking in
an MPEG-TS file with a start_time it not only transforms (start_time +
input_ts_offset) to (input_ts_offset), but just to 0 :) .
Example:
ffmpeg -v verbose -debug_ts -itsoffset "1616090389" -i
'https://megumin.fushizen.eu/samples/switchingaudio.ts' -c copy -bsf:a
aac_adtstoasc -movflags dash+frag_discont+delay_moov -vframes 5 -f mp4
- > test.mp4
Probed start_time:
Duration: 00:00:15.25, start: 19516.478644, bitrate: 23823 kb/s
And how ffmpeg.c then adjusted it:
demuxer -> ist_index:2 type:audio next_dts:NOPTS next_dts_time:NOPTS
next_pts:NOPTS next_pts_time:NOPTS pkt_pts:1756483078
pkt_pts_time:19516.5 pkt_dts:1756483078 pkt_dts_time:19516.5
off:1616070872521356 off_time:1.61607e+09
demuxer+ffmpeg -> ist_index:2 type:audio pkt_pts:0 pkt_pts_time:0
pkt_dts:0 pkt_dts_time:0 off:-19516478644 off_time:-19516.5
Thus, ffmpeg.c is not only adjusting the timestamp to start at zero
with the start_time, but also takes the itsoffset off as well.
This affects formats with AVFMT_TS_DISCONT flag, ffmpeg checks for a
discontinuity and readjusts the file offset to make output timestamps
smooth.
Add -dts_delta_threshold 1616090389 alongside itsoffset to prevent this
readjustment. Perhaps, both the itsoffset and ts_scale adjustments
should be moved to after the discontinuity checks.
Regards,
Gyan
_______________________________________________
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".
