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by zRedShift 1459 days ago
FLAC compression is, although lossless, not nearly as straightforward as raw PCM/WAV/AIFF. It has LPC (linear predictive coding), with the usual residual entropy/RLE coding (but without the quantization stage, due to being lossless). Also an optimization for when there's stereo input and both channels are very similar, (where it converts it losslessly to mid-channel and side-channel, where the values in side-channel are very small and lend themselves to RLE/entropy coding).

As far as the xiph.org audio codecs go however, Opus is the real magnum opus (pun obviously intended). SILK (the LPC part, donated by skype) + CELT + DNN (used to detect whether it's speech or music to tune the 2 codecs since libopus v1.3), it's quite complex, and I feel like some of its parts (specifically the SILK encoder, which has the donated implementation and only the high level details in its RFC, since CELT has a plethora of documentation/articles and independent encoder re-implementation in ffmpeg) are only really understood by the original authors (or at least were when they wrote them a decade and a half ago). Reverse engineering the (SILK) encoder code and making a video similar to the one on the OP (or at least an article/blog post) could be a fun activity.
1 comments
Sesse__ 1459 days ago
Opus feels like it solved the problem of audio compression. Even if someone came out with a codec that gave same quality at half the bitrate, I don't think I would care much; I just want Opus in all my devices, everywhere. :-) It's good enough along pretty much all axes, except, of course, universal support.
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zRedShift 1459 days ago
If we're talking about wish-lists, encoding performance on low-power IoT devices, maybe? It has decent SIMD support on ARM/x86 and tweakable complexity settings, but if your device is weaker than an ESP32, you'll be hard-pressed to encode audio in real time, even on the lowest complexity.

The new kids on the block in the speech encoding/real time communications space (Google Lyra/Microsoft Satin) have fancy AI models, promise decent quality in ultra-low bitrates (3-6kbps), but don't look like they're any easier to run on micro controller.

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lifthrasiir 1459 days ago
How about Codec 2 [1]? I think it delivers a comparable performance to Lyra etc. while not using ML, and has multiple ESP32 ports already. Maybe it might be usable for less powered devices.

[1] https://www.rowetel.com/?page_id=452

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