Audio Slowly gets out of sync

[sirius247]

Hello,
I'm trying to add a second audio track to a mkv file.

The second track comes from an avi file which i extracted using AoA Audio Extractor. I Then used belight making sure the Sample Rate was 48000Hz and the bitrate at 192kbps which the original audio track is set at.

Then using mkvmerge i set the delay for the audio track a second back to sync up the audio and video. Then merged it.

When playing it starts perfectly then slowly goes out of sync more and more into the movie till the point where the audio is totally in a different scene then the video.

I left the delay option alone to see if that was doing it but it was not.

How do i fix this?

BTW the avi file is 23.976fps and the MKV is 25fps.

Thanks in advance

[manono]

BTW the avi file is 23.976fps and the MKV is 25fps.

Don't you think that might have something to do with it? Either speed up the audio to match the 25fps video, or slow the video (and the original audio) to 23.976fps.

[sirius247]

BTW the avi file is 23.976fps and the MKV is 25fps.

Don't you think that might have something to do with it? Either speed up the audio to match the 25fps video, or slow the video (and the original audio) to 23.976fps.

Yep just did that and am getting the same results.

I used Belight, maybe i should try something else to speed up the audio to 25fps. Any software suggestions?

[johns0]

How did you speed up the audio?

[sirius247]

How did you speed up the audio?

In Belight i clicked on advanced settings and selected "Convert framerate from" and inputed 23976 to 25000

and then ran BeLight

[sirius247]

OK tried something different,

I extracted the h264 video file using mkvextract. Then using mkvmerge GUI i change the framerate under 'Format specific options' to 23.976024.

Then i merged that file with the audio file.

It is PERFECT at first, then the audio starts going faster then the video now!!
lol

Im out of ideas

[Calidore]

Fixing the framerate is a start, but the real issue is simply length. You said this audio track was from a different video, so apparently the length isn't a perfect match. Get the _exact_ length of both the audio file and the video it's going on, divide, and then stretch/shrink the audio as appropriate before grafting it on.

Example: When I'm using Virtualdub to convert a 25 fps video to 23.976 fps (I _hate_ the PAL speedup effect), I use its advanced "stretch" audio filter with a ratio of 1.04271. Perfect sync, every time.

Audacity has a stretch function, but the early version I used to use only went to two decimals, which wasn't precise enough for movie-length files. I don't know if current versions are better; otherwise, I'm sure someone here can recommend an audio tool that will do it.

[johns0]

Audacity lets you stretch or shrink with better precision now,up to .001 change.

[AlanHK]

Use Audacity's "Change tempo" effect; you specify either percent or the exact length of the new audio.

[johns0]

Use Audacity's "Change tempo" effect; you specify either percent or the exact length of the new audio.

You might want to use the change speed if you want the pitch to match the original file.

[sirius247]

Ok thanks for the help guys.
Now how would i use Audacity? I loaded my extracted ac3 audio file into it. and then Selected it all, when i go to change speed im not sure exactly what to put in?

My video file length is: 43:11 and the audio is: 43:07

I played around with the change speed but when i export it as a mp3 i ended up getting a blank file 8kb in size.

Not sure what im doing wrong

BTW. I installed Lame Encoder so this should work..
Also cant use VirtualDub as it wont read my MKV(original video) file