[Help] Sync separate audio track to mkv file

Hello again,

This sounds like a very simple task but I can't make it work. I've been using MKVToolNix-Gui to mux audio and video but the audio won't sync.
Audio file is a foreign track that contains the french dub of the film that I would like to include in the mkv file. Audio was extracted from an avi file (Dvdrip). Both files, the Dvdrip and the mkv are identical. Same length, no different logos at the beginning, no extra scenes.

Here's the media info of the extracted audio file:


Format                      : AC-3
Format/Info                : Audio Coding 3
Commercial name            : Dolby Digital
File size                  : 287 MiB
Duration                    : 2 h 5 min
Overall bit rate mode      : Constant
Overall bit rate            : 320 kb/s

Audio
Format                      : AC-3
Format/Info                : Audio Coding 3
Commercial name            : Dolby Digital
Duration                    : 2 h 5 min
Bit rate mode              : Constant
Bit rate                    : 320 kb/s
Channel(s)                  : 2 channels
Channel layout              : L R
Sampling rate              : 48.0 kHz
Frame rate                  : 31.250 FPS (1536 SPF)
Compression mode            : Lossy
Stream size                : 287 MiB (100%)
Service kind                : Complete Main


And the media info of the video:

Format                      : Matroska
Format version              : Version 4
File size                  : 12.0 GiB
Duration                    : 2 h 5 min
Overall bit rate            : 13.7 Mb/s
Encoded date                : UTC 2010-02-22 21:41:29
Writing application        : no_variable_data
Writing library            : no_variable_data

Video
ID                          : 1
Format                      : AVC
Format/Info                : Advanced Video Codec
Format profile              : [email protected]
Format settings            : CABAC / 4 Ref Frames
Format settings, CABAC      : Yes
Format settings, Reference  : 4 frames
Codec ID                    : V_MPEG4/ISO/AVC
Duration                    : 2 h 5 min
Bit rate                    : 13.3 Mb/s
Width                      : 1 920 pixels
Height                      : 1 080 pixels
Display aspect ratio        : 16:9
Frame rate mode            : Constant
Frame rate                  : 23.976 (24000/1001) FPS
Color space                : YUV
Chroma subsampling          : 4:2:0
Bit depth                  : 8 bits
Scan type                  : Progressive
Bits/(Pixel*Frame)          : 0.267
Stream size                : 11.4 GiB (95%)


I've been told to change the fps of the video to 25 on MKVToolNix before mux since it's possible the Dvdrip was made from a PAL disc. It didn't work, audio is still out of sync. Any ideas what am I doing wrong?

[Kynch]

How is it out of sync? Is it constantly out of sync by the same amount throughout the film or does it gradually go out of sync?

I believe it's constant. If the desync increases as the film goes on it's barely noticeable.

[Kynch]

Then I guess you need to find out by how much it's out of sync and remove some audio at the beginning or the end.

I'm not the best person to ask for this, I would open the film and the separate audio source in a video editor to find out exactly how out of sync they are and trim the audio that way.

Ok, I'll try that. Thanks for the reply.

[alleycat]

Best way I find is play the file in VLC, use J and K on your keyboard to adjust the audio until it gets to the point that it is in sync. Make a note of the plus or minus figure and then download a program called delaycut. Open the audio file in that, enter the delay and adjust the file. Then mux it to an MKV with the new audio file, play it again in VLC, check it's all in sync, if not repeat the process.