[Cin] MKV containers

[Phyllis Smith]

Andrea, I did a little bit of experimentation with mkv this morning and can
at least pass along some observations.

> every time I use mkv format (with any codec) it always comes out in the
> terminal the string:
>   "FFMPEG::open_decoder: some stream times estimated:
> /home/paz/video_editing/prova/MyVideo.mkv"
>
This does not cause any real problems.  Basically, when you open a file, if
a stream has a known duration, there is no message.  It really should have
a duration but it often obviously does not.  If the duration is unknown, it
is estimated by:
     using File Size and Bitrate to estimate the duration
anyway, the stream number cinelerra uses versus ffmpeg for mkv may be
counted differently (per gg).

> In these cases the file management, both in playback and rendering, is
> much heavier. For example, a rendering of two mkv files (x264) of
> about 1 Gb in total takes more than an hour, while similar mp4 files
> (x264) take 25 minutes.


In my experience, if you look at the size of the files generated, the mkv
file is a lot smaller so I believe that that is why it is so heavy on the
CPU usage and takes twice as long to generate.  I do not see much
difference when I increase the number of "threads" used or modify the
"speed" parameter.  AV1 files have this same small size / slow render issue.

Is there anything I can do about it? I would
> love to be able to use containers and codecs associated with mkv. Have
> others had similar experiences?
>

The only thing I have been able to do to speed up the rendering to take
less time is *modify "crf" to a higher number* - allowable values range
from 0-63 and the cin-gg opts files have it set to 32 which is considered a
good setting to use.  When you click on the wrench in the video render
menu, you see crf=32 and you can change it there.  I could not tell if the
quality difference of using crf=45 (which is supposed to be of lower
quality and runs faster) is detrimental or not. It really looked the same
to me but I used a low resolution video.  And the time savings helps but it
still slower than using mp4.

You have probably already looked at the following URL, but that is what
Frederic Roentz referred to often:
    https://developers.google.com/media/vp9/settings/vod/
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