Replacing audio in a MP4 (with Vdub)

[Asterra]

Hmm. Here's what led me to this. I got this movie whose audio is about 150ms out of sync. The movie is an H264+MP3 in MP4. Vdub refused to load the video, even after I installed the latest ffdshow with its Vdub plugin options checked. I was eventually able to determine that Vdub can support Directshow filters with a plugin, so I went that route.

It loaded the video fine. It extracted the audio fine. I did my edit, saved as a new MP3, and pointed Vdub at the new MP3. But now when I go to save as a new AVI, it complains that

"The source video stream uses a compression algorithm which is not compatible with AVI files. Direct stream copy cannot be used with this video stream."

Rubbish, I say, because I already losslessly converted the MP4 to a fully functioning AVI using MP4Cam2AVI. In fact, I say, let's see what happens when I load that AVI into Vdub now.

Well unfortunately, even though the AVI is completely valid and playable, Vdub (with the Directshow plugin, mind) refuses to load it, complaining - as it did with the MP4 prior to the plugin upgrade - that it

"Couldn't locate decompressor for format 'H264' (unknown)
"VirtualDub requires a Video for Windows (VFW) compatible codec to decompress video. DirectShow codecs, such as those used by Windows Media Player, are not suitable."

So my problem seems to be any of the following:

1: Can't get Vdub to recognize / handle H264 without an all-purpose Directshow plugin.
2: The Directshow plugin seems not to work in some cases.
3: The Directshow plugin seems not to enable Vdub to actually save anything without fully processing it, which defeats the whole purpose.

Any takers? ;p

[Baldrick]

Use avidemux instead. Change the audio->shift to 150ms. Save as new mp4.

Don't use virtualdub if you want to save as mp4.

[Asterra]

Thanks for the quick reply as always. Here are my results.

Avidemux notifies me:

"H.264 Detected. If the file is using B-frames as reference it can lead to a crash or stuttering. Avidemux can use another mode which is safe but YOU WILL LOSE FRAME ACCURACY. Do you want to use that mode?"

I chose "no". It then said

"Index is not up to date. You should use Tool->Rebuild Frame. Do it now?"

I did. It crashed.

So I chose "no" again and then chose "no" to the re-indexing. Loaded fine this time. But every attempt to save a video resulted in a file that refused to successfully play in any media player. The player would recognize the video resolution, but give up beyond that. This included replacing the audio with an MP3, shifting the audio, shifting and saving the audio as PCM (just in case), and even saving the entire video/audio completely unaltered.

This left me with little choice but to choose "yes" to the safe mode which loses frame accuracy. But even this gave the same results: Files which refused to play a single frame.

The only modest success I've had is with the AVI file I created earlier from the MP4 using MP4Cam2AVI. It loaded the file fine, and the frame rebuilding went off without crashing. However, inexplicably, the resulting video file played at approximately twice its original speed. Bummer.

The final thing I tried was loading the AVI and replacing the video's audio with my custom MP3. The resulting file is _almost_ what I was after. The audio is now in sync, per my adjustment to the audio file. The only problem is that the first few seconds (prior to some critical I-frame, one supposes) has frozen / corrupted video.

To recap, the road to my modest success involved:

1: Extracting the audio with Vdub.
2: Modifying and recreating the audio.
3: Converting the original MP4 to AVI with MP4Cam2AVI.
4: Loading the converted AVI into Avidemux, refusing the "safe mode" but allowing the frame rebuild.
5: Replacing the audio with the recreated audio.

I imagine that if Avidemux did not crash when loading the unmodified MP4 (as it warned that it had a tendency to), things would have been much simpler, with a better result.

[k.]

Did you try changing the audio delay with Yamb?

[Asterra]

Excellent.

Yamb did the trick. Rather than using any built-in audio delay (which I never found anyway), I just imported my custom mp3 from earlier. Viola, playable file with audio fixed and no corruption. I could have done it all without using Vdub. So yeah, this program works. Thanks for the tip.