ac3 - interval and preload

[loni_blues]

Hi,

I am trying to encode a movie with the original ac3 track in it. In the Interleaving & Avi-overhead section there is an option about frames. The default is 1. When I get to the section DivX Encoding Control Panel and select the ac3 track, I get a value for Interval (which is the same value in frames I previously selected in the Interleaving & Avi-overhead section) and another value for preload. Do any of these values have to be modified? What do they mean?

Thanks for any help,

Loni Blues

[len0x]

The values on the Encode window never have to be modified:
- default preload is OK
- interval as you saw is always the same as selected on the bitrate tab

In general interval=2 frames is a good idea (actually the more frames you select the less interleaving size you get)...

[loni_blues]

Thanks, len0x!

Loni Blues

[aramo]

I read once that using a multiple of 64ms for the preload was a good idea - I've been using 256ms for R1 and 320ms for R2 for the preload for some time now and it works well.

[loni_blues]

@aramo

Sorry, I don´t understand what you mean by R1 and R2.

Loni Blues

[aramo]

oops sorry just shorthand for Region-1 & Region-2. TBH I do this without thinking, it's worked flawlessly for many many movies.

Region Preload(ms) Interval(frames)
1 256 2
2/4 320 2
0 probably same as R1

[len0x]

Some ppl indeed have problems with preload & interval when ac3 plays improperly afterwards... I _never_ managed to get bad ac3 muxing in more than 300 movies I encoded. May be it's playback problems on some systems ?

[aramo]

Len0x your probably right about the source of audio muxing errors - gKnot is very good at getting it right. The last time I had a problem [using default preload values] was Dec-2001, the movie was 'One flew over the Cuckoos Next'. Shortly after that I switched to 256/320ms preload values and I don't recall having had an audio related problem since. Having said that I've maybe 100 movies done with default preload values and bar 1 or 2 none of them had audio problems either.

To answer loni_blues original question :) My understanding is at the preload is the amount of audio loaded into memory before software starts to replay the video .. a sort of audio cache. The interval [1 or 2 frames] is how frequently the audio component is folded into the avi file. It sorta makes sense that there should be a relationship between the preload and the interval e.g. preload = 4*interval, for R2 dvds 320ms = 8 frames [4*interval], R1s are not so neat.