Audio delay in VirtualDubMod 1.5.10.1

[Killstun]

I have an AVI, which i like to put together with an AC3 stream (AC3 T03 3_2ch 384Kbps DELAY -272ms.ac3). I set the correct delay value (-272ms) in Audio Skew Correction and set the correct Preload/Interleaving value (160/160ms) in Audio Block Placement. So far so good. Then I save as AVI.

But if I later open the file in VdubMod and want to edit and cut the new AVI file, do I then have to set the Audio Skew Correction and Preload/Interleaving values again for the AC3 T03 3_2ch 384Kbps DELAY -272ms.ac3 stream, or have the two streams (AVI/AC3) been "melt" together for good?

[Matthew]

VirtualDubMod deals with negative audio delays by chopping off the beginning of the AC3, so when you reextract the audio, it will have an audio delay of 0.

However, each AC3 frame is 32 ms, so as 272/32=8.5, you will have half an AC3 frame (16 ms) at the start of the stream. This is junk data.

So, given the junk data at the front, it might be necessary to run the extracted AC3 through besplit in order to delete it. Then remux with a positive delay of 16ms. vdubmod will just insert half a frame's worth of 0s.

Now, ooops, after writing all that I've just read your question properly. If you are just cutting (not extracting the audio), then there is no problem as the audio/video is melded together and you are not undoing that.

[Killstun]

Thx alot Matthew :-) Just have one question more. Do the same thing apply for the Preload/Interleaving value? Noticed that standard is 500/1, so would that interfear when cutting once again, or can I just ignore that setting (maybe by turning off audio/video interleaving)?

PS. What does "offset audio to maintain a/v sync" do?

[Matthew]

Interleaving/preload affects how the streams are muxed. So as long as you are not separating the audio and video streams when doing your editing then you shouldn't have a problem. You shouldn't need to fiddle with any of the streamlist settings if you are just cutting the avi.

The offset audio thing I imagine would just do what I said in my previous post, chop the audio or add 0s. To be honest I'm not sure what would happen if you uncheck it ;o I'm much more into demuxing avis, rather than creating them =)

BTW if I recall correctly 500/1 is only appropriate for muxing mp3. AC3 requires different settings, can't remember what they are, but they should be obtainable via the search. If you get them wrong you may get playback issues like desync. The interleaving settings won't change one byte in the audio and video streams themselves, so you can always demux/remux later if the settings turn out to be troublesome.

[jult]

PS. What does "offset audio to maintain a/v sync" do?I was wondering the exact same thing.
It's VERY confusing to say the least, to put that below both interleaving offsets and skew offsets.
Strange to not put it in the FAQ or Help or any of the documents with VdM.