Audio interleaving? What is it?

[GangstaRap]

i mean, i know what it's literally means but what is it used for and how is it working?

Thanks for anyone who try to help!

[jagabo]

A typical video file will contain both audio and video. If all the video was at the start and all the audio at the end the player would have to seek back and forth to fetch the video and audio to play it back. This will usualy work on a hard drive because they can seek very quickly (all the seeking may make the drive noisy though). But on slow media like CD or DVD you won't get smooth playback. The solution is to interleave the audio and video data. In the file it's saved as a little video, a little audio, a little video, a little audio... Often you'll have one frame of video followed by a frame's worth of audio, etc. But different interleaving options are available. The idea is to keep the audio associated with each video frame close together within the file. This allows the drive to read the file sequentially rather than seeking back and forth all the time. You rarely have to worry about this, the programs that deal with it usually know what they're doing.

[GangstaRap]

jagabo,
i got it...
thanks for that...

You rarely have to worry about this, the programs that deal with it usually know what they're doing.

i have an AVI with out-of-sync audio and i just thought this might be the cause...
i guess its not...

my audio starts O.K but gradually losing sync (preceding)...
is expanding the sample rate above 48000 Hz will fix it?
if it is - how can i do that?

[jagabo]

my audio starts O.K but gradually losing sync (preceding)...
is expanding the sample rate above 48000 Hz will fix it?
if it is - how can i do that?

That wouldn't be an interleaving problem. Changing the sample rate probably won't fix it. What you might be able to do is change the running time of the audio or video.

Many audio editors have the ability to stretch or compress the audio, changing pitch or not. The free Audacity, for example.

You can change the frame rate of the video with a program like AviFRate. Doing this will be OK on a computer but may not work well if you're making a DVD.

[tinker]

Changing sample rate will only change audio fidelity not length. You have to do what jagabo suggests.

[hech54]

my audio starts O.K but gradually losing sync (preceding)...
is expanding the sample rate above 48000 Hz will fix it?
if it is - how can i do that?

Are you talking about Interleaving in VirtualDub?

[GangstaRap]

thanks for the help...

Many audio editors have the ability to stretch or compress the audio, changing pitch or not. The free Audacity, for example.

how can i stretch the audio with Audacity?

You can change the frame rate of the video with a program like AviFRate. Doing this will be OK on a computer but may not work well if you're making a DVD.

i want to be able to play it later on DVD...

Are you talking about Interleaving in VirtualDub?

yeah...
why?

[jagabo]

how can i stretch the audio with Audacity?

Use the Effect -> Change Speed option. Export the audio from VirtualDubMod as uncompressed AVI, open with Audacity, mark the entire audio (Ctrl+A), goto Effect -> Change Speed, enter the percent change, press OK, Save. Use that as the new audio source in VirtualDubMod.

[GangstaRap]

OK...
how can i calculate the percent?

here's the video info:


Thanks for the great help!

[jagabo]

You said the audio starts out in sync but after a while it gets ahead of the video, and presumably, gets farther and farther ahead of the video. At the end of the video measure how far ahead the audio is. Say the audio ends 10 seconds before the video (if it's hard to tell exactly when the audio ends, look for something you can syncronize to near the and of the video) and the video is 90 minutes (5400 seconds). So the audio is 5390 seconds long but needs to be 10 seconds longer: 10 / 5390 * 100, or ~0.185529 percent longer. That is the value to enter in Audacity.

[hech54]

Are you talking about Interleaving in VirtualDub?

yeah...
why?

If the audio corrects itself in VirtualDub after you press Stop then Start...then
the audio should be fine. VirtualDub is a TERRIBLE player. Editors in general
are terrible players.
I've used VirtualDub Mpeg many times to correct audio sync issues....and I learned
NOT to let the video run too long when checking my adjustments.
This point/fact was pointed out to me by someone here at Videohelp too.