Nulls in Audio = delay?

[AlanHK]

This takes a little description.

I have some AVI files with MP3 sound. When demuxed and converted to MPEG for DVD authoring in the usual way some go out of sync.

Looking at the demuxed sound files, these are MP3, but the ones with the sync problem do not play in many audio players. Looking at them in a binary editor, I see about 20k of nulls at the head of the file before any other data. Presumably this corresponds to a delay of about a second, as that's how much out of sync the MPEG version is. When I transcode these with Besweet it apparently just discards the zeros, so losing sync.

I tried using VDUBMOD in full processing mode to save the audio out as a wave, but it fails with the error "ACM reported error in audio decompressor".

However, the AVIs do play with sound in sync in VLC and MPC, so they must interpret the nulls correctly. Is there a way to use either to export a plain WAVE?

I tried the "decompress" utility from AVI2VCD, but that loses sync after conversion.

Or failing that, is there a way to read off the delay equivalent of the nulls?
I can apply a delay to the MPEG audio, but it would be nice to have a number rather than just trial and error and looking for doors slamming.

[guns1inger]

It sounds like these have been encoded to MP3 with a variable bitrate> Most encoders seem to have issues converting these, and sync problems result. Install the LAME MP3 codec, then try with Virtualdubmod. Make sure you set the compression to Uncompressed PCM before saving your wav file.

[redwudz]

VD Mod should have mentioned the existence of MP3 VBR audio if that was detected.

Probably a dumb question, but are you sure they are MP3 audio? I mention this because of your statement; 'ACM reported error in audio decompressor' with VDM.

That sounds like maybe AC3 audio that can also cause MPEG encoder sync problems at times. For VirtualDub Mod, I use the AC3 ACM Decompressor if I need to save them to WAV. But if they are AC3, you wouldn't need to do anything but demux them as they would likely already be DVD compliant.

Or am I misreading all that?

[AlanHK]

VD Mod should have mentioned the existence of MP3 VBR audio if that was detected.

Probably a dumb question, but are you sure they are MP3 audio? I mention this because of your statement; 'ACM reported error in audio decompressor' with VDM.

That sounds like maybe AC3 audio that can also cause MPEG encoder sync problems at times. For VirtualDub Mod, I use the AC3 ACM Decompressor if I need to save them to WAV. But if they are AC3, you wouldn't need to do anything but demux them as they would likely already be DVD compliant.

Or am I misreading all that?

I don't understand the "ACM" error message, but the sound is definitely MP3.

AviCodec says :
Audio : 41 MB, 117 Kbps, 48000 Hz, 2 channels, 0x55 = MPEG Layer-3, Supported

And I got the usual stupid question from VDUBMOD about VBRs.

As I said, I think the problem about these is due to the zeros at the head of the file.

Looks like I have to resync these the hard way.

[guns1inger]

If you got the question, then it is VBR. If you have LAME installed then it should be able to read it. Answer Yes to the warning, then save it out as uncompressed PCM audio.

[AlanHK]

If you got the question, then it is VBR. If you have LAME installed then it should be able to read it. Answer Yes to the warning, then save it out as uncompressed PCM audio.

That's the way it should work, and I've done that many times before when VBRs were causing problems. But not in this case. VDUBMOD and VDUBMP3freeze both choke when asked to process them.
I already have Lame installed.

I'd just say the MP3s were "bad", but they do play perfectly in VLC and MPC.
So the nulls in the MP3 must be significant.

[Soopafresh]

Alan - I don't know if this will help at all, but it might assist you with sync if you run out of ideas.

http://www.surina.net/soundtouch/soundstretch.html
http://thunder.eeap.cwru.edu/~zhuo/audioscale.html


Also, maybe Yamb 1.6 is smarter when it comes to demuxing. Not sure, though.

http://yamb.unite-video.com/download.html