Smallest possible with 5.1 Sound?

[Waldbaer]

Hello,
What is the smallest possibility to encode a movie with ffmpegX without losing the surround sound of the source? It's important for me because I now have a 5.1 sound system and I'd like to exploit it, too! 8)
I've tried DivX with AC3 sound, but somehow it does not work. ffmpegX encodes the movie, but if I try to play it, VLC won't put out any sound. I can check under "information" and it finds the AC3sound track and even recognizes it as the right format, but it does not play it.
Is there a possibility to make h264-movies with surround sound? Is there any audio format which can have 5.1 sound and ffmpegX or some different free- or shareware can convert to?

[major]

Surround sound is not 5.1, it is stereo with a special treatment of the signal.

[Waldbaer]

Yes, you'll be right that not every channel is encoded seperately, otherways the files had to be bigger. But it's not only a decoding affair, is it? Because then it would be senseless to write onto a DVD "5.1 Dolby Surround Sound".
And I don't get this extra controlled effect in movies, if I encode it down to stereo. But that effect is what I actually want. Of course I can just expand the stereo sound to 6 channels, but this doesn't give the effect of for example things flying around, and also the automatic 5.1 Dolby Surround decoder doesn't succeed in the intended effect, because he just doesn't know where to position a special sound of the stereo sound in the room - how could he?

Any tips for my question?

[major]

No, I mean, Dolby Digital is 5:1, Dolby Surround is 2:0. So when you say "Surround" people are expected to understand 2:0.

[Waldbaer]

Oh, thanks for making me pay attention to this!
I renamed the topic and corrected everything to prevent this misunderstanding.
I want to have 5.1 sound in the encoded movie. And I'm still waiting for ideas! It's no problem for me to keep the size of the Dolby Digital audio stream, but I want to compress the video smaller than the original DVD (still keeping more or less the quality, of course).

[dylanpank@msn.com]

FFmpegX can only encode to 2:0 stereo or mono. If you want 5.1 surround, you must choose AC3 pass through, which will simply copy the original 5.1 soundtrack into the avi file you encode. In fact it's not connected to the video file size at all., but since 5.1 surround sound is usually enncoded at 384, or 448Kb/s you're looking at around 300MB just for the sound depending on the movie length. This is one of the reasons most DivX avis fit on two CDs, as for a reasonable quality vide, they have to be big to fit the sound.

The surround sound Major is talking about does have the effect of things flyinfg around, uit's called matrixed audio, where 4 channels are fitted into 2 stereo tracks, it's a neat trick, and almost all Hollywood films with stereo 2.0 sound use this technique, if you have Dolby Pro Logic compatible equipment it can decode this 4 from 2 surround sound. Some programmes will mix 5.1 into a surround stereo mix, Does FFmpegX do this? I gather the encoding matrix isn;'t that tricky (it basically involves putting the back speaker channels out of 90 degrees out of phase with each other, cutting off certain frequencies and then dropping the front and rear signals by 3dB).

[Waldbaer]

Yes, you're right, but I already knew these things more or less. I said, that I accept that the audio of a movie may be about 300 MB, so quite big, but the video is still much bigger. A DVD movie is usually about 5 GB, but using a compression like DivX you can squeeze him at about 1,4 GB (yes, two cds). And if I use the 5.1 sound it may be 1,6 GB, but that's not the problem since I want to store it on my harddisks.
The problem is that DivX-.avi with the ac3 audio stream doesn't work with my players, just like I did say in my first post in this topic. That's why I'm looking for alternatives, but as far as I can see, there is none which gets similar results, because h264 doesn't support 5.1 sound at all until now, am I right?
Does anybody here have experiences with DivX with 5.1 audio?

[major]

DVD ffmpeg supports encoding to AC3 5.1 audio (you must disable "Normalize audio"). DivX AVI does not support AC3 without nasty hacks. Encoding AAC 5.1 HE is not currently supported but this should become available within some time.

[Waldbaer]

Encoding AAC 5.1 HE is not currently supported but this should become available within some time.

This sounds good.
And then, also h264 movies with 5.1 sound will be possible, I think (and hope)?