On 21.11.2016 12:41, Hendrik Leppkes wrote:
On Mon, Nov 21, 2016 at 11:35 AM, Sampsa Riikonen
<[email protected]> wrote:
Hi,
At the current development branch, setting
AVStream->time_base
does not have any effect on the final stream time base anymore..!
(in earlier versions there where the codec time base and the stream time
base, and one had to do "av_packet_rescale_ts" when giving the AVPackets to
the muxer).
Whatever I put in the stream time base, the matroska muxer always writes
into the file header (you can check this with "mkvinfo -g filename.mkv")
like this:
Track => default duration => 1000 ms ("1000 frames/fields per second for a
video track")
Timestamps for individual frames are ok, but media players, live vlc, fail
miserably when seeking such a file.
.. in order for them to do decent seeking, they need the timebase to reflect
the actual frame rate of the video stream (i.e. for 20 fps "track => default
duration => 40 ms").
Unfortunately, in "avformat.h":
-------
...
* etc.) as known. The @ref AVStream.time_base "stream timebase" should
* be set to the timebase that the caller desires to use for this stream
(note
* that the timebase actually used by the muxer can be different, as will
be
* described later).
...
* information on the packets sent to the muxer must be in the corresponding
* AVStream's timebase. That timebase is set by the muxer (in the
* avformat_write_header() step) and may be different from the timebase
* requested by the caller.
-------
Why was this implemented? Is there any way to force the timebase to a
certain value?
You can set the default duration by setting AVStream.avg_frame_rate,
if thats not set then it'll use the time_base for that.
Thanks Hendrik - it worked.
As a side note, I discovered that older vlc(s) (like version 2.2.2 that
comes with stock ubuntu 16) require the 20 fps timebase in mkv muxer,
but the latest git pull (vlc 3+) doesn't mind
the timebase being the default 1 sec.
Regards,
Sampsa
I don't see anything that would overwrite the time_base in matroska, though.
- Hendrik
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