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Surround vorbis
electrick
post Sep 14 2010, 23:01
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I'm ripping movies to mkv files with x264 video and surround vorbis sound (5.1 or higher). What's might be the lowest bitrate or quality level used to not destroy the surround channel effects?
Also, so far I have only figured out how to rip dvd. If I get around to bluray, some movies use 7.1. Is vorbis good for 7.1 also? And do you think it has a future?
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odyssey
post Sep 15 2010, 00:53
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I'm probably in for some bashing here, BUT:

I did some tests a while ago, to find a way to compress AC3/DTS more than the usual 384kbit found on DVD's. I tried both AAC and OGG - The results? Not good... They aren't optimized for multichannel. The way I understand it; they don't do something similar to "Joint Stereo" to optimize bit-usage. I wasn't able to lower the bitrate much more than the 384kbit without sacrifying audible quality, and then it's quite pointless. Therefore I keep the AC3 track when I "Handbrake" my DVD's into x264 smile.gif

QUOTE
And do you think it has a future?

Blurays store the audio in much higher bitrates. You may be able to benefit more from transcoding these to a lower bitrate. You can use eac3to to do that.

Really, I think the future is not so limiting on the storage-side. I would much rather keep the encodings as they are and just buy a larger harddrive, now they are so cheap smile.gif

This post has been edited by odyssey: Sep 15 2010, 00:58


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andy o
post Sep 15 2010, 01:21
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Is there a reason to recompress audio though? 640kbps for DD in blu-ray seems more than sufficient, and probably the most compatible multichannel format there is. Pretty much the same for DTS. Blu-rays come with either an embedded DD track when the main one is TrueHD, and DTS has the DTS "core" on DTS-HD, which can be extracted very easily.

As for 7.1 audio, I'm one of the early adopters, and very very few movies (and even fewer good ones) make any use of it.

Also, a good reason not to recompress is that your decoder can then apply metadata such as DRC and DPLII(x), or DTS-ES matrix.

This post has been edited by andy o: Sep 15 2010, 01:25
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electrick
post Sep 15 2010, 01:51
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QUOTE (odyssey @ Sep 14 2010, 16:53) *
I'm probably in for some bashing here, BUT:

I did some tests a while ago, to find a way to compress AC3/DTS more than the usual 384kbit found on DVD's. I tried both AAC and OGG - The results? Not good... They aren't optimized for multichannel. The way I understand it; they don't do something similar to "Joint Stereo" to optimize bit-usage. I wasn't able to lower the bitrate much more than the 384kbit without sacrifying audible quality, and then it's quite pointless. Therefore I keep the AC3 track when I "Handbrake" my DVD's into x264 smile.gif

QUOTE
And do you think it has a future?

Blurays store the audio in much higher bitrates. You may be able to benefit more from transcoding these to a lower bitrate. You can use eac3to to do that.

Really, I think the future is not so limiting on the storage-side. I would much rather keep the encodings as they are and just buy a larger harddrive, now they are so cheap smile.gif


How long ago did you do those tests? The only reason I'm considering it now is because the update to libvorbis 1.3.1 mentions something about 5.1 optimizations. Is that all hype? And what is wrong with joint stereo? I understand it's actually a great way to reduce size without reducing sound quality. I seem to remember reading some flame wars around here about the very issue of the mp3 joint stereo inferiority being a myth.

QUOTE (andy o @ Sep 14 2010, 17:21) *
Is there a reason to recompress audio though? 640kbps for DD in blu-ray seems more than sufficient, and probably the most compatible multichannel format there is. Pretty much the same for DTS. Blu-rays come with either an embedded DD track when the main one is TrueHD, and DTS has the DTS "core" on DTS-HD, which can be extracted very easily.

As for 7.1 audio, I'm one of the early adopters, and very very few movies (and even fewer good ones) make any use of it.

Also, a good reason not to recompress is that your decoder can then apply metadata such as DRC and DPLII(x), or DTS-ES matrix.


I'm not doing this to store any material. I'm still going to keep the discs around. The idea I have behind this is to have them for playback on the PC without messing with the discs, and perhaps to carry around on a smartphone. Another reason is that I use linux and playing a bluray selection on there is pretty ridiculous. You pretty much have to rip just to watch. Not that bluray playback is much better on windows with all that restricted hardware and drm stuff. But either way if I encode this, it will be batched and I'd like it to be as optimized as possible.

This post has been edited by electrick: Sep 15 2010, 01:53
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Alex B
post Sep 15 2010, 02:59
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I think Monty's recent work on surround Vorbis is astonishing.

Here are some links:

http://xiphmont.livejournal.com/48207.html
http://xiphmont.livejournal.com/48863.html
http://www.xiph.org/press/2010/vorbis-surround/
http://xiphmont.livejournal.com/49385.html
http://people.xiph.org/~xiphmont/demo/index.html

I have not yet done any listening tests and without good lossless source files they would be transcoding tests anyway.

I agree that it does not make sense to transcode AC-3 or DTS to surround Vorbis, but it would a great audio format for original releases (assuming the audio track is encoded from the original lossless master). Something like 720p AVC + surround Vorbis in mkv container would be a fine format for on-line delivery.


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http://listening-tests.freetzi.com
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electrick
post Sep 15 2010, 03:19
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Thanks for confirming that.

Unfortunately, I don't have any lossless source. But I still can't tell the difference between ac3 and a transcode. I don't know any audiophiles for a test. I'm 99% sure that all the people I know wouldn't be able to tell the difference on my speakers. You can see a significant size difference between these:

AC3 sample
Vorbis transcode

Either way, seems like a big step up from the mp3 channel downmixes I used to do.

This post has been edited by electrick: Sep 15 2010, 03:20
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odyssey
post Sep 15 2010, 07:44
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QUOTE (electrick @ Sep 15 2010, 01:51) *
How long ago did you do those tests? The only reason I'm considering it now is because the update to libvorbis 1.3.1 mentions something about 5.1 optimizations. Is that all hype? And what is wrong with joint stereo? I understand it's actually a great way to reduce size without reducing sound quality. I seem to remember reading some flame wars around here about the very issue of the mp3 joint stereo inferiority being a myth.

1 or 2 years ago. If the changelog says something about 5.1 optimizations, you should really try it out - Sounds like something that were not available when I conducted the tests smile.gif Read my post again regarding Joint Stereo - I'm not saying it's a bad thing.

Another thing: How much do you expect to be able to compress them? 192kbit? 224kbit? - Maybe less?? I gave up on it because the gap up to the 384kbit were too small to give much benefit.


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