Experimental release of Ghost/CELT 0.0.1 Options

[jmvalin]

I've just made the first public release of some new *experimental* codec work I've been doing (part of the vague Ghost project) with help from Monty and Timothy. This is mainly intended for developers with DSP knowledge, not for doing anything useful with it (but it does encode and decode already). Also, the main idea is *not* to replace either Speex or Vorbis, but to code audio with really low latency -- currently 8 ms.

This is still very experimental and everything is still likely to change, including the exact goals. The algorithm is called (temporary name) Code-Excited Lapped Transform (CELT) and the main ideas are:
- Using an MDCT on very short frames
- Dividing into 15 bands and transmitting the energy for each band
- Using a pitch predictor (good for speech, but helps for music as well).
- The rest is coded using a unit-pulse codebook.
At this point, I'm still trying to figure out how to fit psychoacoustics into this.

CELT is based on a paper I submitted to ICASSP and which I'm hoping will be accepted so I can make it available to everyone. The only difference is that the ICASSP paper was based on the FFT (non critically sampled), whereas this version is based on the MDCT. One part that is already published though is Tim's explanation of the pulse codebook encoding.

The full source for CELT is available at: http://downloads.us.xiph.org/releases/celt/celt-0.0.1.tar.gz or through git at http://git.xiph.org/celt.git

I've put some music samples at 56 kbps CBR at http://people.xiph.org/~jm/comp_celt58cbr.wav with the original at http://people.xiph.org/~jm/comp44.wav . As you can hear, it definitely doesn't suck as much as Speex on music, but there's still room for improvement.

I'm open to interesting ideas, but don't bother complaining if it doesn't work or if it explodes in your face :-) Oh, and don't expect a final codec any time soon.

Have fun!

[Kef]

I've just made the first public release of some new *experimental* codec work I've been doing (part of the vague Ghost project) with help from Monty and Timothy. This is mainly intended for developers with DSP knowledge, not for doing anything useful with it (but it does encode and decode already). Also, the main idea is *not* to replace either Speex or Vorbis, but to code audio with really low latency -- currently 8 ms.

This is still very experimental and everything is still likely to change, including the exact goals. The algorithm is called (temporary name) Code-Excited Lapped Transform (CELT) and the main ideas are:
- Using an MDCT on very short frames
- Dividing into 15 bands and transmitting the energy for each band
- Using a pitch predictor (good for speech, but helps for music as well).
- The rest is coded using a unit-pulse codebook.
At this point, I'm still trying to figure out how to fit psychoacoustics into this.

CELT is based on a paper I submitted to ICASSP and which I'm hoping will be accepted so I can make it available to everyone. The only difference is that the ICASSP paper was based on the FFT (non critically sampled), whereas this version is based on the MDCT. One part that is already published though is Tim's explanation of the pulse codebook encoding.

The full source for CELT is available at: http://downloads.us.xiph.org/releases/celt/celt-0.0.1.tar.gz or through git at http://git.xiph.org/celt.git

I've put some music samples at 56 kbps CBR at http://people.xiph.org/~jm/comp_celt58cbr.wav with the original at http://people.xiph.org/~jm/comp44.wav . As you can hear, it definitely doesn't suck as much as Speex on music, but there's still room for improvement.

I'm open to interesting ideas, but don't bother complaining if it doesn't work or if it explodes in your face :-) Oh, and don't expect a final codec any time soon.

Have fun!

Cheers! It's nice to see there is activity from the xiph organization. I haven't tried your new codec yet but it is definitely the next thing on my to-do list.

Now, I know this is not your "thing" or your responsibility but what about Vorbis and Theora? There's been very little activity on both fronts and as user and proponent of open source applications, I am deeply concerned to say at least. Vorbis is a great codec and my music collection is > 50% Vorbis right now (and the rest mp3) but the lack of activity, except the tunings of Ayomi, makes it very difficult to continue using it.
It's like Vorbis has been completely abandoned by xiph and I believe this is one of the reasons why people start to look for alternatives. I think this is at least one of the reasons why the Vorbis usage has dropped significantly the last two years here at HA.

http://www.hydrogenaudio.org/forums/index....showtopic=60145
http://img406.imageshack.us/my.php?image=lossydi7.png

Please at least make Ayomis tunings into the official branch at xiph. There are many companies which only use the official xiph released versions of Vorbis (like http://www.hbr1.com/ for example) and the latest tunings are from 2004... Not a good sign.

Not even to mention Theora, which was donated by On2 in 2002. It's now 2008 and it's still in beta stage and the quality is closer to mpeg-1 than mpeg-4...

Please don't take this criticism personally. It's not anyone's fault. But some development form xiph's side would be great. Instead of focusing on future codecs, why not maintain those you already have? SPEEX and FLAC are doing great. Vorbis and Theora, not so great. If I was a better programmer than I am , I would not hesitate to join xiph and at least try to help out but the sad fact is I'm simply not up to the task, at least not now, and the only thing I can do is to write crap on internet forums as I have proved today.

Anyway, thank you for your time and please forward my concerns to the xiph foundation. Thank you for your great work with Speex!

/Kef

[jmvalin]

Now, I know this is not your "thing" or your responsibility but what about Vorbis and Theora? There's been very little activity on both fronts and as user and proponent of open source applications, I am deeply concerned to say at least. Vorbis is a great codec and my music collection is > 50% Vorbis right now (and the rest mp3) but the lack of activity, except the tunings of Ayomi, makes it very difficult to continue using it.
It's like Vorbis has been completely abandoned by xiph and I believe this is one of the reasons why people start to look for alternatives. I think this is at least one of the reasons why the Vorbis usage has dropped significantly the last two years here at HA.

http://www.hydrogenaudio.org/forums/index....showtopic=60145
http://img406.imageshack.us/my.php?image=lossydi7.png

Actually, Theora has been under <b>very</b> active development in the past few months by Monty (see http://svn.xiph.org/branches/theora-thusnelda/). As for Vorbis, there are still some things to improve, but it's already quite mature. Keep in mind that it's not because you don't see anything that we're not doing anything. That being said, we do have a "resource" problem. All of us have day jobs, little of which involves Xiph codecs. If more people helped instead of complaining that nothing's done, we'd be moving much faster. BTW, not everything we do requires advanced signal processing knowledge. All the time we spend maintaining websites, fixing documentation, makefiles, ... is time not spent on the core codecs.

[johnsonlam]

Keep in mind that it's not because you don't see anything that we're not doing anything. That being said, we do have a "resource" problem. All of us have day jobs, little of which involves Xiph codecs.

Most of us here know you developers have a hard time working day and night, thank you very much.

All we can do is waiting patiently, hopefully a few lines of text one or twice a month can ease the pain of the people waiting endlessly.

Thanks again.