VirtualDub VBR audio stream detected

[sdsu2pop]

I'm trying to lower the bitrate of a xvid file from 1500 kbps to 1000 kbps but when I opened the file with VirtualDub I got a popup saying that VBR audio stream was detected and said it will rewrite the audio header with standard CBR values. It also said if this is unacceptable, decompress the entire audio stream to an uncompressed WAV file and recompress with a CBR encoder.

I thought the popup wasn't a big deal so I encoded it anyway but after the movie was encoded, the audio was out of sync 5-10 seconds. So is the whole decompress/uncompress/recompress a long process? Is there a shortcut to just get the video bitrate lowered? If not, is there a guide to fix the audio problem?

[jagabo]

You can usually do it right in VirtualDub. Open the file in question. Ignore the message. Select Audio -> Full Processing Mode. Then File -> Save WAV.

Since you've already re-compressed the video you can use that video with the new audio. Open the video file as usual. Select Video -> Direct Stream Copy so the video isn't recompressed. Then select the WAV file as the audio source with Audio -> WAV Audio. Select an appropriate audio codec for compression (MP3, CBR?). Then Save as AVI again.

If that doesn't work you can use some third party audio program (Audacity, BeSweet, many commercial products) to extract the audio as WAV, then use that new WAV file as the source.

[redwudz]

What jagabo said. And here's a guide:

https://www.videohelp.com/virtualdubaudio.htm

BTW, it's a good system to learn. MP3 VBR audio is unfortunately common with Xvids. It causes even more problems with a MPEG encoder.

[manono]

Since all he wants to do is recompress the video to a lower bitrate, keeping the original audio, what's the point of first converting the audio to WAV and then converting it again back to MP3, wasting time and further degrading its quality?

There's nothing at all wrong with having VBR MP3 in an AVI. It gives better quality when compared to CBR at the same bitrate. Since VDub doesn't support VBR MP3 audio, he'd be better off using VDubMod for the encoding job. He can either click no to that stupid message and Direct Stream it, or he can demux the audio as is, encode without the audio, and then mux it back in after the video is reencoded.

[whitejremiah]

unfortunately (and ive seen this a lot, too) VBR MP3 can and will goof up a LOT of video conversions and in some cases, even playback.........this can affect the video very little in some cases, in other cases, it can make the audio as far as 10-15 seconds off...i suppose your right if he JUST wants to drop the video bitrate some (though i see no point in that either.....) converting the audio to CBR can and will fix a lot of problems if he was ever to want to convert it to a differant format (i.e. vcd, svcd, dvd)

[jagabo]

He can either click no to that stupid message and Direct Stream it, or he can demux the audio as is, encode without the audio, and then mux it back in after the video is reencoded.

He can try that but in my experience those options usually leave you with out-of-sync audio. Hence the recommendation to reencode with CBR.

[manono]

...if he was ever to want to convert it to a differant format (i.e. vcd, svcd, dvd)

Except we're not talking about a different format. And problems along those lines are generally caused by encoder incompetence.

Here's how I would do it. Open the AVI in VDubMod (NOT VDub). Click no to the message. Go Streams->Stream List->Demux and demux the MP3 audio. Open the AVI again, go Streams->Stream List->Disable the audio. Choose the Codec (Xvid), set it up for the 2 passes at the bitrate he wants, encode and then mux the MP3 using Nandub or VDubMod when done. I'd use AviSynth for the job and resize down since he's cutting the bitrate by a third, but I guess that's asking too much. If there's a synch issue at the other end, it will have been caused by an unknown delay initially. You'd get the same thing after converting to CBR. It's easily fixed with a couple of tries.

If you mux back in the unchanged VBR MP3 audio (excepting for the possible delay, as mentioned before), there's no possible reason to have playback problems or synch issues, assuming you reencoded to the same framerate and use a decent player. The original plays fine, doesn't it? Many of these problems are caused by the use of VDub. Why use it if it doesn't even support VBR MP3. I got rid of it a long time ago.

[sdsu2pop]

Thanks for all the help guys. I wish I tried using VirtualDubMod earlier because it turns out that all I had to do was choose "No" when I got the popup message. In VirtualDub, I could only choose "OK" because that was the only option. So everything is working fine now