Porcuswiki: With ffmpeg 7.0, it has so many implementations that it might be worth a wiki page.

2024-04-08T15:54:10Z

With ffmpeg 7.0, it has so many implementations that it might be worth a wiki page.

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The '''Quite OK Audio Format''' (QOA) is a niche [[lossy]] audio [[codec]] created by Dominic Szablewski in 2023. It designed to be, in the author's words, ''lossy, simple and quite ok'': "simple" to computers in terms of decoding speed (intended to close in on [[ADPCM]] speeds at better quality<ref>[https://qoaformat.org/ QOA at qoaformat.org]</ref>) and to humans in terms of the format specification, which fits a single page<ref>[https://qoaformat.org/qoa-specification.pdf QOA specification] (CC0 licensed)</ref>. It is not intended to compete with current lossy encoders in terms of near-transparency at low bitrates – indeed, "low" bitrates are arguably not possible at the sample rates that yield "quite ok" quality.

QOA is available as a free and open-source (MIT licensed) library. Its github repository<ref>[https://github.com/phoboslab/qoa QOA at github]</ref> links to alternative implementations; also, ffmpeg can decode it (from version 7.0). A third-party [[Foobar2000:Components/QOA_Audio_Decoder_(foo_qoa) | foobar2000 QOA playback component]] is available (note the warning given).

==Properties==
(Disclaimer: Part of the following is taken from the author's initial presentation<ref>[https://phoboslab.org/log/2023/02/qoa-time-domain-audio-compression "Time Domain Audio Compression at 3.2 bits per Sample"] (blog post introducing QOA)</ref>, which pre-dates the current version.)

* QOA is a CBR format, spending 3.2 bytes per sample per channel, each channel encoded separately. In addition, there is a frame header per 5120 interchannel sample, and a file header.
* Bit rate is then defined by sample rate, which could be from 1 to 2<sup>24</sup> Hz in integer steps, and by channel count. For 44.1 kHz stereo, bit rate will then amount to 277 kbit/s.
* Multichannel support: Format allows for 255 channels. A decoder is ''required to'' support 1 to 8 channels, possibly varying over frames (channel allocation coinciding with [[FLAC]] frames' channel allocation).
* Encoding method: Like several audio formats, it works with a predictor from past samples (fourth order). The residual – i.e. the difference between "predicted" and "actual" sample value in the source signal – is then replaced by one out of eight hard-coded values (this is the [[lossy]] part).

The reference implementation is 400 lines of C code. The format can encode fast, but it is also possible to try to improve quality by spending computing effort on noise shaping upon encoding, selecting the residual value in a more clever way than naive roundoff<ref>[https://hydrogenaud.io/index.php/topic,123838.msg1024296.html#msg1024296 Hydrogenaudio discussion thread]</ref>.

==References==
<references/>
[[Category: Codecs]]

QOA - Revision history

Porcuswiki: With ffmpeg 7.0, it has so many implementations that it might be worth a wiki page.