OGG 5.1 or AC3?

[Atak_Snajpera]

Let's say that I want to encode lossless 5.1 (True-HD :D ) to smaller file (48khz 16bit 5.1) and the question is which one would offer better quality at the same size. I suppose OGG should give better quality. Do you agree?

[Skelsgard]

Let's say that I want to encode lossless 5.1 (True-HD :D ) to smaller file (48khz 16bit 5.1)
Lossless and bitdepth/samplerate are 2 different concepts. As you stated True HD, I assume you mean 96kHz 24 bits to 48kHz and 16 bits.
You first need to downsample the file with a high quality resampler (i.e. SSRC) and then load the file into an encoder.
As for encoding quality, you can make your own conclusions from the listening tests in the audio sections or in the Hydrogen Audio forums.

Cheers.

[shon3i]

You can use AAC and keep 96khz/24bit, but bitrate should be around 500kbps

[HeadBangeR77]

Some consider Vorbis 5.1 as not mature enough, but I'm no expert at all, so you're gonna trust your own ears, providing you've got suitable audio hardware there.

As shon3i pointed out, AAC (free Nero Encoder) is another option, VBR as the first as well (who needs CBR?).

If AC3, then Aften - Skelsgard could tell you much more about it, and we've got a thread on Aften's developement here.

cheers,
HDBR77

[Skelsgard]

Some consider Vorbis 5.1 as not mature enough, but I'm no expert at all, so you're gonna trust your own ears, providing you've got suitable audio hardware there.
Also, OGG can have some issues regarding mapping when decoded by different decoders, i.e. a DirectShow filter might show wrong mapping while Winamp's decoder shows correct mapping.

If AC3, then Aften - Skelsgard could tell you much more about it
Ha ha, I wish I WAS that smart, but I´m not :D . Still, Aften is by all means a great encoder.
AC3 will ensure you at least compatibility with SAPs if you ever want to port the file to a DVD player or some of the like.

Cheers

[shon3i]

AAC (free Nero Encoder) is another option, VBR as the first as well (who needs CBR?).
I thinked for CT encoder, because IMHO always have better multichannel encodings, but nero is a good option.

[khagaroth]

Don't use Vorbis (ogg) as it's multichannel support is quite miserable. Among other things, the channel coupling isn't working, so there is a lot of wasted bitrate. Sad thing is, the guys from Xiph doesn't bother and instead they are playing with Theora :confused: , what a waste.

[gameplaya15143]

AFAIK vorbis does support lossless channel coupling for 3+channels. It just doesn't support lossy coupling :(

If I was looking for ~250-300kbps I would probably use vorbis. If something like 384-640kbps then I would use ac3.

... well, on second thought.. I would just use vorbis :)