Optimising audio within AVI's for DVD conversion.

[baldrick45]

Ok - One of you experts is gonna know this and some of you may think it's a stupid question but hey ... You gotta learn these things.

I've been given a long movie in AVI format 2h 20mins or thereabouts. Came as 2 chunks with audio in AC3. Both chunks played fine but joining them in VirtualDubMod led to audio sync going off around the join (Quite badly - around 2.5 seconds) . Fair enoughski. Back to the chunks, load them in VDM and select full processing and save the audio as 2 Wav files. (after a quick trip to freecodecs.com to get their ACM decompressor codec).

Join the Wavs in audacity. add the result as a new stream to the single avi (while disabling the original soundtrack). Happy days - perfect audio sync throughout and since it's PCM the conversion to DVD goes perfectly and audio stays in sync. As any readers of my previous posts may recall I normally start with ConvertXtoDVD and change tactics as problems arise...

But the DVD does have a problem - the video quality is now sh*te. Thinking a little further, I believe this is due to the fact that I ended up adding a 1.5Gig audio track to an 900Meg video file. I presume converting the resulting 2.4Gig file to a 4.7Gig +R didn't leave enough available headroom to give me decent quality video. (This kinda assumes the big PCM file would be largely retained in the file Vob format and would not have gone through a conversion to MP2 as part of ConvertX doing it's thing). Is this a correct assumption?

If so, what is the optimal conversion for the Wav before I remux it with the video and then convert to DVD? Intuitively I'd guess a nice CBR MP3 format might give me the smallest file size while being likely to survive it's subsequent trip through ConvertXtoDVD without screwing up the audio sync in the final VOB files again.

Am I on the right track at all or am I talking complete piles of poo?

Answers on a postcard to....

[steveryan]

Seems a long process to me Try loading the two AVI's into AVIdemux, select copy for audio and video and save them as one file. This has worked for me when VDM failed.

[redwudz]

I can see a couple of other methods, though steveryan probably has the easiest way. Why not just drop both halves of the original video into ConvertXToDVD? Or, now that you have the WAV, run it through ffmpeggui and convert to AC3 and use that when you convert with ConvertXToDVD?

Usually I convert the individual audios to AC3, then put the videos only through an encoder like TMPGEnc or similar, taking into account the audio size. Then when I author with TMPGEnc DVD Author, add the videos and audios in and let TDA 'add' them all together. Since you already had AC3 (Hopefully DVD compliant) you shouldn't have to process it at all. I wouldn't convert it to MP3 as that many manipulations will damage the audio quality.

I'm not sure why ConvertXToDVD didn't convert the audio from PCM to MPEG or AC3 in the first place? Does it show as PCM in the output DVD file?