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Bitrate Peeling with Ogg Vorbis
Yort writes "Thought this might be interesting to some audiophile /.ers - there's been some discussion on the Ogg Vorbis lists, summarized in the most recent Ogg Traffic, about "bitrate peeling". In short, it's where you can simply "peel off" the high resolution data from the ends of an audio stream packet to come up with a smaller, lower quality stream. Brings up a number of geek-cool opportunities."
"Beni Cherniavsky mentioned a very intriguing counterpart to bitrate peeling. If you have a peeler that saves the bits it chopped off, you could reconstitute the higher quality files by adding the missing bits to the lower quality file. This idea could lead to a music download service where you can download a low quality preview version of a song, and if you are interested, download the missing bits to make it a high quality version."
Or, Slightly modified, You could share all your high quality oggs on a P2P network, and have your client peel it down to 'future-legal-to-share' low quality files.
Pain lasts, kid. Its how you know you're alive. Sometimes I think this growing up thing is just pain management-TheMaxx
Well, you should try then one simple test, that I did for myself and my friends. I just ripped a track of one of my favorites CD and encoded it with my favorite MP3 encoder (lame) to 160, 192, 256 kbps. I then burned a new CD-R with four tracks (original, 160, 192 and 256) in a random order. Since then, I'm looking for someone to be able to put those tracks in the right order.
No one has been able to until then, and I'm not only talking (only) about average people. I have some friends which (unlike me) have a decent equipment.
Usually these guys were able to clearly distinguish 160kbps from the set. With 2-3 pass they detected the 192kbps track and they couldn't tell the difference between the 256kbps and the original.
Maybe I could send you guys some samples...
Just keep in mind also that MP3 is the same type of compression than DTS & AC3 (Dolby Digital) and I've never heard someone complain about those (especially DTS). If you're unhappy with quality, just increase bitrate. And if those guys in the MPEG consortium felt that 320kbps should be the maximum, It should mean something.
Lossless compressors have such a poor ratio!
Write boring code, not shiny code!
One thing that hasn't been discussed here is that a lot of people feel that Vorbis is transparent at something like quality setting 4. Other people think it's transparent at quality setting 3. Others think it's great at 1. I release my stuff at 4, but bitrate peeling will let people peel those down to what sounds good to them. Maybe they want to monkey with it, and maybe they don't, but the option to do this without re-encoding is sexy.
It's not just a 'chop it down for modem folks' thing, it's also a letting people choose for themselves situation that I think is more important.
Features are cool, but features that give people options apart from 'use it or not' are even cooler.
That's it for me. Please donate to Xiph.org, and then go listen to some tunes. Enjoy!
Scalable techniques like this are very cool, but hardly novel.
MPEG-4's scalable profiles provide a similar effect (albeit in the other direction, with enhancement layers). Some of the higher end audio codecs (beyond CELP and AAC), like ER BSAC (Error Resistant Bit Sliced Arithmetic Coding) do exactly this. The idea in this case is that the server will in real-time only provide as many bits as the connection can currently provide. Very nice for wireless.
QDesign's QDX format does almost exactly what is described for Ogg, with arbitrary bitrate peeling down to the 1 Kbps level. The idea is that you could copy as much data as you want to your mobile player, and it'd dynamically thin to the data rate that would fill up your device.
And still image codecs like JPEG have used progressive modes for years, where additional data adds more detail to the image.
My video compression blog
There aren't ANY free lossy codecs that can do bit-peeling right now. Some non-free codecs allow you to overlay data (like progressive JPEG), which is NOT the same thing. That's just like transmitting deltas at higher compression rates, which could be done with a simple side-band for any existing method, MP3 even.
The only option is transcoding, which compounds compression errors (decode, reencode). I often wished the MPEG group would have been more intelligent in the design of their bit-allocater so that you could "thin out" the quantization of the power bands by looking at the "right parts" of the MP3 frame. Alas, this is not possible.
But the Vorbis designers have made this possible, thus making it possible to have high-quality and low-quality versions derived from the same source file without additional processing. I imagine you have certain restricted choices, due to how quantization information is bundled up/packeted. But it isn't just sexy, it would be stupid to NOT DO IT. It takes just a little forethought on how to lay out the information in a hierarchial fashion. What makes anyone think that this is any harder then decoding/reencoding. I guarantee it has a time complexity on the order of a straight copy.
Hell, formats like SHN and FLAC can do it, just substitute short codes for long codes at a certain rate; it'll add a bit of wide-band energy on decode, raising the noise floor in proportion to the space savings you gain.
So anyway, "poop on you" to all these wanna-be audiophiles/slashdot-know-it-alls who don't no a good thing when they see it.
Don't like it, keep sucking on that Layer III.
THIS THING CAN TURN ON A DIME, MACROSSZERO STYLE ALSO FUCK BETA, ~NYORON