CELT 0.9.1 is out!, Help wanted Options

[jmvalin]

Hi,

I'd like to announce CELT version 0.9.1. There have been many quality enhancements since 0.8.x and even more so since the last version announced on HA. You can get it from the CELT website. Also, CELT is now a component of the Opus codec, which is in the process of being standardized by the IETF as a lossy audio codec for interactive applications.

Also, for those who would like to help, we are looking for volunteers to help tune the codec. The bit-stream is (finally) about to be frozen, so any quality improvements we can get before then is useful. No highly specialized skills required, just good critical listening abilities. As a first round, I'd be interested in comments and rankings of the following four audio files:

fileA.wav
fileB.wav
fileC.wav
fileD.wav

The bit-rate is fairly low (64 kb/s), so artefacts are easy to hear. This is the original (uncompressed) file. I'm interested in a quality ranking of all these four files (especially the ones that sound similar). I'll reveal the contents of these files after people have responded.

[sauvage78]

Personnaly I have some interest in it, but I need a win32 command line encoder/decoder to test it my way. I am moderately interested in testing how it competes nowadays against aotuv & nero aac in a self-made single test, but I am not interested to help for development in the long run... specially if it doesn't compete well & specially on already encoded wavs which are not my own selection of killer samples. (In short I am interested in a very selfish test serving my own needs & I don't care what others may think of my test). Anyway I am not in a hurry to test it because if ever it would beat aotuv (which would mean it has improved a LOT since V0.52 ... which it certainly has considering how many updates there were since V0.52) then it will be frustrating to have all the aotuv zealots on my back for teaching them that Vorbis would likely be dead ... I wish that CELT would be the new messiah but having seen in the past how musepack/vorbis/aotuv development has stalled when their developer interest slowed down, I suspect that, sooner or later (hopefully later), CELT will follow the same fate, so honestly I am much more interested by an open source aac equivalent to x264 developed by a team, which I think would be more future proof, then I will ever be by a xiph codec developed by a loner (no matter how clever he is). My only problem with aac is its non-native & non-robust gapless support via tricky deletable tags. I like the robust vorbis gapless support & I think CELT might inherit this which is why I still have some interest in it. AAC already perfectly suits my needs for blu-ray audio part encoding because gaplessness is not needed there.
If ever CELT beats aotuv then we will end up with a better-then-vorbis codec with no [f2k-cuetools-eac3to-mkv-5.1-rockbox] support, which would be an annoying (but hopefully temporary) situation.

All this put together made that if I do have some interest in CELT, I always plan to test it ... later. I use flac for CD & nero aac for blu-ray & CELT alone is unlikey to change this. My small interest for CELT is due to 2 possibility both with unlikely probability:
1: I run out of HDD space because my 5 HDD sata (the 6th one is for SDD) are full, then I will need CELT. (Only if I don't favor lossywav)
2: Webm becomes better than x264, then I will need CELT. (... but I don't believe in Santa Claus anymore)

As you see CELT beeing trapped in the family of Xiph codecs, & this family of codec being non-competitive (x264 beat webm/theora, & nero aac beats aotuv), even if CELT alone would become the perfect lossy codec (the quality of nero aac with the robust gaplessness of vorbis) that doesn't mean it would be enougth for me to use it, because CELT is "bonded by blood" to a sub-optimal family of video codecs. (Using it would mean mixing mpeg with xiph in mkv which I tend to avoid.)

I know it may sound discouraging, but I only explain all that for you to understand why I didn't anwser to your request for me to test CELT one month ago.
Just like lossywav, I like CELT on paper, but I just don't use it in real life actually.

Sorry for not answering your pm directly a month ago (jmvalin), I was too lazy & short of time to write this down. Furthermore I was fearing that you wouldn't like much my opinion about the actual state of lossy codecs.

To sum up according to me, CELT is in a very paradoxal situation, where it might have become a real challenger for aotuv & nero aac, but because of its missing features/missing support/non-mpeg status, even if it would be the best codec around, I would likely not use it ... well at last not untill an eco-system was built around it.

I don't want to be the only guy on earth knowing that CELT is (maybe) the best pure lossy codec around, so I just don't test it to avoid the headache ... I know it's a vicious circle, but it's not my problem, I leave the frustration to ... IgorC [no you don't need to thks me, man ]

This post has been edited by sauvage78: Feb 5 2011, 05:20

[jmvalin]

A few things I'd like to say here about CELT to answer some of questions and address some misconceptions. First, CELT has gone a long, long way since 0.5.2. In fact, there were more changes since 0.5.2 than there were from the beginning to 0.5.2. Among the things that changed is that CELT now supports longer frame sizes than you tested earlier (20 ms vs 5 ms) though the smaller frame size is still supported. Another difference is that it now supports VBR. On top of that, there's been a huge number of other changes. I'm sure if you tested again, the results you would get would be a lot different than with 0.5.2. I recommend you listen to the samples on Monty's CELT demo page (if you hear clicks in the samples when played from the web page, it's a browser bug and you should download them directly), which has some comparisons with Vorbis and AAC. The 32 kb/s and 48 kb/s samples aren't that useful (below the sweet spot), but the 64 kb/s ones should give a good idea of the quality. Of course, CELT also scales up to 510 kb/s for stereo. Also, if you look at IgorC's results, you'll see that CELT actually beats Vorbis aotuv on most samples, though of course the results vary from one sample to another.

As for you comment about "As you see CELT beeing trapped in the family of Xiph codecs", you should know that CELT is actually one half of the Opus that is currently being standardized at the IETF. The other half is Skype's SILK codec. So practically speaking, CELT is likely to see very wide deployment, starting with Skype. As I've pointed out before, CELT's main focus is *interactive* audio, which means it can give very good audio quality for real-time applications (unlike MP3, Vorbis and HE-AAC). To achieve that we've had to do some sacrifices, but even despite that, the quality is competitive with that of the AAC family. And the same codec can actually work from 6 kb/s (speech) to 510 kb/s, rather than having different profiles for different bit-rates and applications (HEv1, HEv2, LC, LD, ELD). So being standardized at the IETF means we're no longer talking about just a single developer or organization.

As for the tools, don't worry, that's the next thing on the list once the bit-stream is frozen. Which brings up another point. The bit-stream is currently in soft-freeze, so there's a short window of time where the codec is in a pretty good state, but we can still fix any issue that would be discovered before the bit-stream is officially frozen. So I definitely recommend you try CELT again. If binaries are a problem, I may be able to get someone to make Win32 ones. Alternatively, I can provide you with encoded samples.