from Hacker News

The Quite OK Audio Format for Fast, Lossy Compression

by smlckz on 8/8/23, 11:27 AM with 63 comments

  • by kragen on 8/9/23, 8:24 PM

    has anyone benchmarked qoa to see roughly how many instructions per sample it needs? all i see here is that it's more than adpcm and less than mp3, but those differ by orders of magnitude

    like, can you reasonably qoa-compress real-time 16ksps audio on a 16 megahertz atmega328?

    hmm, https://phoboslab.org/log/2023/04/qoa-specification has some benchmark results, let's see... seems like he encoded 9807 seconds of 44.1ksps stereo in 25.8 seconds and decoded it in 3.00 seconds on an i7-6700k running singlethreaded. what does that imply for other machines?

    it seems to be integer code (because reproducibility between the predictor in encoding and decoding is important, and a significant part of it is 16-bit. https://ark.intel.com/content/www/xl/es/ark/products/88195/i... says it's a 4.2 gigahertz skylake. agner says skylake can do 4–6 ipc (well, μops/cycle) https://www.agner.org/optimize/blog/read.php?i=628, coincidentally testing on an i7-6700k himself, but let's assume it's 3 ipc, because it's usually hard to reach even that level of ilp in useful code

    so that's about 380 μops per sample if i'm doing my math right; that might be on the order of 400 32-bit integer instructions per sample on an in-order processor. if (handwaving wildly now!) that's 600 8-bit instructions, the atmega328 should be able to encode somewhere in the range of 16–32 kilosamples per second

    so, quite plausibly

    for decoding the same math gives 43 μops per sample rather than 380

    i'm very interested to hear anyone else's benchmarks or calculations

  • by g0xA52A2A on 8/9/23, 7:46 PM

  • by mips_r4300i on 8/10/23, 9:43 AM

    Comparing against 4bit ADPCM, which is already able to give quite good performance as long as your sample rates are relatively modern, this only improves it to 3.2 bits. It is fast, but ADPCM is also fast.

    Would be nice to see joint stereo support. If you were to take ADPCM or this OK format and try to encode any stereo music with it, you will need 2 channels. However, there is an extremely advantageous optimization that can be made here - most music is largely center panned, so both channels are almost the same. With joint stereo you record one channel (either by picking one or mixing to an average) and then you can store the difference for the other channel which will occupy a lot fewer bits, assuming you are able to quantize away the increased entropy.

    For example, instead of using two 4bit ADPCM channels for stereo, which would only be a 50% savings over uncompressed, you could probably use an average of 5 bits per sample.

  • by gaazoh on 8/10/23, 10:10 AM

    I like the philosophy of QOA (and other similar projects, including QOI and TinyVG), but unlike others, it seems like it's not ready to use yet, see https://github.com/phoboslab/qoa/issues/25

    > I have just pushed a workaround to master. [...]

    > This still introduces audible artifacts when the weights reset. It prevents the LMS from exploding, but is far from perfect :/

    This, combined with the fact that that issue is still open mean that a breaking change is still to be expected.

  • by codeflo on 8/9/23, 7:52 PM

    It's interesting that this works in the time domain (instead of frequency domain), and I wonder what the resulting quality limitations are, if any. The sound samples on the demo page, at the least the dozen I clicked on, didn't seem all that challenging. Few, mostly synthesized instruments, low dynamic range. My ears aren't good enough to evaluate audio codecs anyway, however.

  • by Pet_Ant on 8/9/23, 6:43 PM

    What is the LFE channel?

    It should be spelled out explicitly, but I figured out the rest

    L-Left,R-Right,C-Center,FL-Front Left,FR-FrontRight,SL-SideLeft,SR-SideRight,BL-BackLeft,BR-BackRight

    ---

    Edit: LFE-LowFrequencyEffects... so subwoofer?

    https://www.dolby.com/uploadedFiles/Assets/US/Doc/Profession...

  • by MobiusHorizons on 8/9/23, 8:39 PM

    Seems to have similar design criteria as opus but I don’t see any comparison.

  • by Turing_Machine on 8/9/23, 7:37 PM

    I looked around, but didn't see any mention of potential patent issues. I assume that this has been considered? The Ogg Vorbis people spent a lot of time on that back when they were developing their format.

    Other than that, looks great!

  • by marcoc on 8/9/23, 8:15 PM

    How can one create a professional looking pdf like the QOAF specification one?

  • by rockstarflo on 8/8/23, 11:28 AM

    What is the tradeoff there?

  • by ape4 on 8/9/23, 6:43 PM

    What's going to be the next Quite OK thing?

  • by ericls on 8/9/23, 10:56 PM

    The smaple page preloads all the files before playing... Which wastes lots of bandwidth.

  • by Aldipower on 8/9/23, 8:44 PM

    An _audio_ format which is _quite_ ok? Not sure, if I need that.