[LAU] OT - syncing partially out of sync video and audio in existing files

[pshirkey at boosthardware.com]

> Excerpts from pshirkey's message of 2011-06-10 21:56:06 +0200:
>> > Excerpts from Ralf Mardorf's message of 2011-06-10 19:24:54 +0200:
>> >> On Fri, 2011-06-10 at 18:57 +0200, Renato wrote:
>> >> > On Fri, 10 Jun 2011 17:58:46 +0200
>> >> > Philipp <hollunder at lavabit.com> wrote:
>> >> >
>> >> > > Hi,
>> >> > > sorry for abusing this list for a mostly video editing question,
>> but
>> >> I
>> >> > > didn't find a proper list and knew that we have some video people
>> on
>> >> > > this list.
>> >> > >
>> >> > > I'd like to fix some videos that have partially out of sync video
>> >> and
>> >> > > audio, meaning that beginning at a certain point in the video the
>> >> > > audio is suddenly out of sync by a couple of seconds. There's no
>> >> > > constant change, the delay seems fixed once it's there.
>> >> > >
>> >> > > I wonder how to fix such a thing. The files are xvid encoded
>> videos
>> >> > > and vbr mp3 audio inside avi containers. I thought it should be
>> >> > > reasonably easy to cut and move the audio (re-encode if
>> unavoidable,
>> >> > > but I know it's in principle possible without) and put it back in
>> a
>> >> > > container, but I didn't manage.
>> >> > >
>> >> > > Can someone recommend a program/workflow that would allow this?
>> >> > >
>> >> > > I tried:
>> >> > > - Avidemux: seems like actual editing is not what this program
>> was
>> >> > >   written for, couldn't figure it out, but it seems close
>> >> > >
>> >> > > - openshot: couldn't figure out how to separate video/audio
>> >> > >
>> >> > > - kino: seems to only work with DV-files, apparently takes ages
>> to
>> >> > >   decode the file, doesn't seem to be what I need
>> >> > >
>> >> > > - openmovieeditor: I figured it might work by dragging the file
>> to
>> >> > > both a video and an audio track, but I got extremely garbled
>> audio
>> >> > > output, no idea what's wrong
>> >> > >
>> >> > > - cinelerra-cv: Doesn't start. No error message, it simply shows
>> no
>> >> > >   window, nothing. Well, it does something with the screen, but
>> it
>> >> > > shows nothing.
>> >> > >
>> >> > > - pitivi: Doesn't seem like it can play back the video. I can
>> drag
>> >> the
>> >> > >   video to the tracks and it starts to draw a waveform, I guess
>> no
>> >> > > video thumbnails because of: gst.ElementNotFoundError: pngenc
>> >> > >   Doesn't seem to be able to play the video.
>> >> > >
>> >> > > - kdenlive: would require me to install 30 additional packages,
>> >> total
>> >> > >   about 200MB, no thanks.
>> >> > >
>> >> > > I thought it would be a simple task, really nothing fancy. Seems
>> >> like
>> >> > > I was wrong.
>> >> > >
>> >> > > Regards,
>> >> > > Philipp
>> >> > >
>> >> >
>> >> > Hi, unfortunately can't give you a full solution, but only a hint:
>> in
>> >> > mplayer with "-" and "+" you can adjust audio/video syncronization
>> by
>> >> > multiples of 100ms (maybe you cand do finer, but I'm not sure).
>> >> >
>> >> > maybe you could then somehow record the output to a new file?
>> >
>> > Thanks Renato, I've played with that already and know the approximate
>> > offsets, but that doesn't help much. I'm not sure screen recorders
>> > typically can pause and resume, and even then it would be less than
>> > optimal anyway due to the transcoding of both audio and video.
>> >
>> > Also, to clarify, those offsets are constant but only appear beginning
>> > at a certain point in the file, imaginary example: after 97 Minutes
>> the
>> > offset is suddenly approximately -9600ms. Hence shifting the offset of
>> > the whole file doesn't help.
>> >
>>
>>
>> I went through this a couple of years back with pretty much the same
>> result. The general consensus round here was that it is not possible to
>> shrink a video to fit with an audio track. Instead you should stretch
>> the
>> audio track to fit the video.
>>
>> I ended up using Blender to edit the video into chunks and align chunks
>> of
>> audio to fit as best as possible.
>>
>> I don't understand why it is not possible to resize a video track. It
>> seems to me that dropping video frames is significantly easier
>> programatically than time stretching audio.
>
> I've only done this with one video so far, so I don't know whether it
> works fine in general, but in this case mencoder dropped a couple of
> seconds that were just black anyway, so no real loss. It was a fade out
> to black and I jugged down the time the moment it was black. I somewhat
> wonder how it was messed up, I suspect files were put together and some
> black frames were added without caring for audio, or something like
> that. Anyways, there's no loss of content with this file, which was with
> almost ten seconds delay by far the worst of the bunch. Ok, according to
> mplayer the file is now 13 seconds shorter instead of 9.55, but who
> cares as long as the result is fine.
>
> So it seems mencoder can just drop video frames.

That's good to know. For references sake, what was the commandline that
you ended up using?


> I was also surprised about the speed. I guess it took at most a minute
> per operation on this old cheap laptop and ~3h video, most likely it
> avoided re-encoding of anything, which is a good thing in my book. In
> contrast, just loading the video into kino would probably have taken an
> hour.
>
> Regards,
> Philipp
>
>