[FFmpeg-user] Transcoding MPEG .ts results in slow playback speed

[Peter B.]

Hi Carl Eugen :)


On 25/01/2019 20:12, Carl Eugen Hoyos wrote:
> (Please do not compress compressed files and no, I don't think
> an md5 sum is necessary in this case, if it is necessary you can
> put it in your email)

You're absolutely right of course.

I usually don't compress compress files (no size gain), but I wanted to
provide a hashcode.
And since I usually leave the samples on my server "forever" I thought a
package might be convenient to keep it tidier (though tar would have
sufficed).


Anyways:
> How did you create this file?
> The file looks as if you used FFmpeg to cut instead of dd...

Not this time :D
We spoke about this last time, so I used dd:

$ dd if=ORIGINAL.ts of=short.ts bs=1k count=8100


> If this is the original file, it is most likely broken but I must say
> it could be interesting to find out what happened...

I'm also curious.
Unfortunately, this file was provided by some private individual to the
archive, so this part of the story is unknown.
But I'll try to find out, as I'm curious how files like these are
created with "regular" workflows :P


> (The file was created with FFmpeg.)

I saw that in the metadata, too:
"service_provider: FFmpeg"
And was surprised, because I'm pretty sure they created it using a GUI.


> You can "fix" it by forcing the input frame rate to "25" but this
> often has unintended side-effects (like desync), setpts should
> have the same effect but may be more difficult to tune.

Interesting!

Works with added "-r 25" before "-i":
$ ffmpeg-git -r 25 -i ORIGINAL.ts -c:v ffv1 -c:a copy out/test-fps25.avi

But how come it requires the 25fps information, when ffprobe, mediainfo
and VLC all say that the source already has 25fps set anyways?

I'm currently reading the docs [1] for setpts... :D


Thanks so far for all your answers,
Peter


== References:
[1] https://ffmpeg.org/ffmpeg-filters.html#setpts_002c-asetpts