Thoughts On AC3Fix

[EpheMeroN]

I have an AC3 in an AVI file I am going to be extracting. The doom9 guides suggest saving it to WAVE, and then running it through BeSliced to generate an AC3 file again. And then there's AC3Fix, which corrects any bad frames in an AC3 file. Does BeSliced do this too? Or is it just good practice to always run your AC3 file through AC3Fix just to be safe?

[mic]

FWIW & all, any time you alter video or audio, you're going to lose some quality. If you need to convert the ac3 to something else, fine, but if you don't need to alter the ac3 in any way, IMHO why bother?

More directly to your questions, there are ac3 utilities to repair & correct timing etc. so you don't have to re-encode, & thus don't have to worry about any quality loss, like ac3fix. A good ac3 file is a good ac3 file, and if it ain't broke, there's nothing to fix -- but if you have reason to doubt, or if it makes you feel better, don't know that running it through ac3fix can cause any prob (at least in my experience -- hopefully someone will chime in if I'm wrong there). Altering/editing/enhancing the audio file normally means converting to wav files, & in theory at least, if you create a new ac3 file it shouldn't need any fixing.

That said, creating a new ac3 file, depending on the software used, can create problems. If you have a workflow in mind, wouldn't hurt to search these forums, looking for problems others have experienced.

[EpheMeroN]

FWIW & all, any time you alter video or audio, you're going to lose some quality. If you need to convert the ac3 to something else, fine, but if you don't need to alter the ac3 in any way, IMHO why bother?
But I don't want to alter my audio at all. I just want to extract the 5.1 AC3 from the AVI so I can use it in a dvd authoring program. I thought extracting the AC3 in Nandub didn't decode the AC3, but simply add a WAVE header to it, and that's why you need BeSliced; to remove the WAVE header?

[Doom9]

I thought extracting the AC3 in Nandub didn't decode the AC3, but simply add a WAVE header to it, and that's why you need BeSliced; to remove the WAVE header?That is correct and just what the guide says ;) Why would you need AC3fix afterwards? is your stream broken or something?

[EpheMeroN]

I do not think my AC3 stream is broken. I just recall the last time I tried to do this and I wanted to reauthor a dvd using GUIforDVDAuthor and it kept crashing. The author of the app told me that some dvd authoring programs (like his) crash a lot of the time when the AC3 has bad frames in it, and suggested always running the AC3 through AC3Fix to avoid issues.

[Doom9]

well, perhaps cutting breaks the AC3 stream, but other than that or a corrupt source to begin with I cannot imagine why an AC3 stream that you demux from an AVI would be bad.

[tebasuna51]

You can use VirtualDubMod (Streams -> Stream List -> Demux) to extract the ac3 directly without wav header.

After you can use BeSplit to fix them. Some ac3 from avi's have extra bytes at the beginning. Inside the ac3 can have corrupt blocks (not compliant with CRC). This two reasons make the dvd soft reject them.

BeSplit fix this two issues if are present, and does nothing if is ok.
If there are many corrupt blocks your ac3 becomes short (32 ms./block)