Advanced AC3 editing question

[perempe]

Hi,

I have a problem with the ac3 audio track.


How can I extend the audio track? The audio ends 4:40 before the movie. The time between the video and audio is growing at a constant speed. (At the half of the movie there is 2:20 time between the video and the audio.)

How can I fix this problem?

[mats.hogberg]

Sounds like it's caused by a frame rate conversion gone bad (25 to 23.976 or 29.97 to 23.976).
In short, you have to decode the AC3 track to wav (stereo), "stretch" the wav (use GoldWave TimeWarp function or WavWorks) and then reencode to stereo AC3. It's theoretically possible to keep the AC3 5.1 (if it is to start with) but the process is long, and requires exotic software, and hardly worth the trouble.
You don't state what your source material is, but if it's DVD/VOB, use ReJig or VobEdit to demux, if it's AVI use VirtualDub.

/Mats

[ChrO]

Hi
You can also use AC3Machine, guide here: http://www.doom9.org/ac3machine.htm
, it is a gui for besweet, and uses ac3enc.dll.
This allows you to stretch the ac3 file so it mathces your framerate.
Regards
Chr

[perempe]

I'll try it.

[Suntan]

Just to add, a freeware program that will do the same thing (in this instance) as Goldwave is Audacity. It is pretty useful if you are looking to do general audio manipulation like this.

-Suntan

[perempe]

The avi is 23.976 frame/sec, so the 25frame/sec playback speed helps a lot, but now there is a constant time between the video and the audio. (The audio is too late by about 17 seconds.)

How can I sync it from the end? I have VirtualDub AC3, but can find other software.

Remember! That audio is AC3 format.

[Suntan]

Try Avi-MuxGUI or vdubmod. They both have a place to add an offset for the audio in milliseconds so a value of 1000 will delay the sound by 1 second, a value of -500 will delay the video by half a second for example. Check out Step 2 on this page: http://www.doom9.org/divx__ac3.htm

-Suntan