Dolby Digital Sound issue with ffmpeg: avi to DVD

[rnabokov]

When I encode an .avi file to PAL DVD using ffmpeg, and using the presets modified only to show DVD, PAL and Best Quality, the resulting DVD's I burn using Toast 6 only play in stereo, even though I have a full 5 channel surround sound system.

What am I doing wrong?

[guns1inger]

how many channels did the original avi file have ?
Chances are it was a stereo source to begin with, so you now have a stereo (2.0) ac3 soundtrack. You cant just create 5.1 out of thin air.

[rnabokov]

D'oh! The original avi file was stereo. I simply assumed that using ffmpeg decoder with the ac3 audio preset option converted the stereo to ac3.

So what can I do - if anything using ffmpeg, to create 5.1?

BTW, using the Tiger version.

[guns1inger]

There isn't much you can do to create a convincing 5.1 from stereo. If you surround system supports Dolby Pro-Logic II you will get a much better experience from letting it do the rear mix than trying to create one yourself. Otherwise, you will have to get out an audio editor and try to create the missing channels.

[rnabokov]

thanks - much appreciate your time and trouble

[celtic_druid]

You can specify the number of audio channels to encode. No idea what ffmpeg does when you set the output to 6 when the input is only 2 though.

If you check the doom9 audio forums there are a whole bunch of methods for 2channel --> 6 audio conversion. Most I think are windows based, however there might be something. As said though, you can't really pull the full channels out of thin air.