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Comment by lucgommans | Hacker News Reader

Adding to this a secondary public service announcement:

I recently learned of Opus (audio codec) and it's amazing. If you've been using mp3, ogg, speex, aac, or any other lossy format: time to upgrade. Opus is freely licensed and I'm blown away by the quality per bitrate. Released in 2012 and I don't see anyone using it yet! Device support is good nowadays and you can either have smaller files or better quality in the same amount of space.

Last night I re-encoded a lot of my audio books (they were mainly mono mp3 64kbps with a few exceptions) and it takes like half the space. One of the larger books went from 1.5GB to 350MB and I can't tell the difference in quality at all.

What I used is apt install opus-tools && opusenc --bitrate x --framesize 60 in.flac out.opus; or choose the Opus export format in Audacity if you're more GUI-inclined.

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Just go lossless. A huge music collection now is, what, 300-500GB in FLAC? That's on the order of 1500-2000 albums, if I've done my orders of magnitude right (about 300MB/album in FLAC).

I re-ripped my CD collection a few years back, and after pondering formats, I realized that for listening around the property, FLAC is perfect (Plex handles it, PlexAmp is nice). And if I really want to stuff more stuff on a smaller drive for the car or something, I can transcode down from FLAC and still have the lossless originals.

It's the same reason my DVD rips from our collection are just MakeMKV wrapping of the original MPEG2. Yeah, I could save some space by transcoding... but disk is cheap, and it's just not worth the hassle. Rip to lossless and go from there.

Depends what you're playing from. I don't have a terabyte of storage on my phone and I'd like to store more than just audio books and music. If you've got a desktop with magnetic storage then sure.

I'd also be curious if you can tell the difference between a 128 kbps Opus and a lossless flac file (in a blind test of course, easy way to test yourself: cp a.flac $RANDOM.flac; cp a.opus $RANDOM.opus; play both with cvlc or something, make your guess, then look at the file size to get the result, repeat at least five times). I could see the argument for having a lossless copy somewhere, just in case you get better audio playback equipment in the future, but for a hot copy (especially on a mobile device) I'm not sure flac is beneficial.

I agree. I was using almost entirely lossless until five years ago or so, when I did some ABX tests (there's a good foobar plugin for those interested) and realised that 256+ kbps LAME was indistinguishable from lossless 24/96 to my ears -- even when actively comparing the two in a quiet room, which obviously is very different to just listening casually while commuting etc.

I kept the lossless files for archival purposes but everything on my phone/laptop is ~320 LAME VBR.

That said, soon after that I switched to Spotify and only rarely listen to my own files now. The convenience and ability to discover new music just doesn't compare.

I suspect that 192k vorbis and 128k opus would also be transparent for you as well (unless you listen to techno/industrial and have really good speakers). Might save you a bit of space.

Yeah that's likely true. I had chosen MP3 for reasons of total compatability and 'good enough' compression, but it seems like almost all music players have good support for those formats as well. Maybe at some point I'll switch over.

MP3 also has some fundamental problems when dealing with short sharp sounds (e.g. castanets), which have been fixed in subsequent audio codec generations such as AAC, Vorbis or Opus.

This also applies to other hardware. Even if you had a terabyte on your phone, no point to lossless if you proceed to play it with cheap earplugs. Not sure if audio controllers in phones are a big influence nowadays.

I use lossless because why not. I have plenty of space on my computer. And if I really like an album that would like to listen on the go, I transcode it to a lossy version (aac)

> ogg

Since we're being sticklers in this thread, ogg is the container, and ogg is a pretty standard container for opus.

Oh, thanks, that's a misunderstanding on my part.

Checking Wikipedia: Ogg is the container and Vorbis/Speex are the codecs. Vorbis and Speex have been superseded by Opus.

Since we're at the PSAs, here is one about Opus: The codec is fixed at a 48kHz sample rate. For your audiobooks that were already low quality it probably doesn't make a difference that there's now one more processing step applied to the audio, but I would never choose Opus as an archival format for music, as there is a lot of content using different sample rates (CDs in particular are 44.1kHz, so there's always a resampling step involved when converting them to Opus). Storage is cheap these days, so for serious archiving FLAC is the only logical choice (but obviously not when the original material was a 64kbps MP3 of course).

In theory, the resampling shouldn't matter, though, should it?

As per Nyquist, as long as the sampling rate is higher than double the highest frequency you care about, the original signal can always be perfectly reconstructed. Therefore going to a higher sample rate shouldn't affect the originally recorded content.

While the "perfect" reconstruction per Nyquist does indeed assume things that aren't actually possible in reality, like infinitely steep filters, AFAIK the best approximations we have are still good enough to not cause any audible issues (all the more so if you're subsequently applying lossy compression anyway), though of course it might be possible that a particular encoder uses a faulty implementation that does indeed mess things up.

Yes, perfect filters don't exist, that's one issue. The other issue is that using Opus now forces you to use that one filter the encoder chose to use. As weird as it may seem, there are various reasons for preferring a lower-quality filters if your source input signal has a low sample rate to begin with (the result may sound fresher due to non-perfect filtering, which can be preferable in some situations). With Opus, the decoder would first have to downsample the 48kHz to the original sample rate, only to upsample them again with a lower-quality filter to achieve the same thing. I think avoiding all those extra steps has its advantage.

> I don't see anyone using it yet

Basically all services use it for realtime voice calls. And YouTube uses it for audio, among other formats.

It's used under the hood indeed, but among hackers (let alone an average person) it's barely known.

Until two days ago, I had heard of the term and knew it was some music format, or perhaps speech encoding, but I had no idea if it was a legacy 90s format or what.

Hence the PSA because I'm blown away by the quality difference (for speech at least, I haven't tried music but Wikipedia says that blind tests also showed better bitrate:quality ratios for music). I've always been using mp3 at ~160 for music and 64kbps for speech (or sometimes AMR in the past) but those days are over now. AAC already should have made me upgrade, but the support is less good (e.g. Android has some lag issues with certain AAC files). Opus works perfectly fine everywhere so far, does great compression on both speech and music, so now I have zero reason to ever go with anything other than MP3 anymore.

Opus is especially space-saving at lower bitrates (as you've discovered). At higher rates the difference is less spectacular, but for non-critical/casual listening (what many of us do most of the time), the space savings (for thousands of files) can be substantial.

[https://wiki.hydrogenaudio.org/index.php?title=Opus#Music_en...]

For everyone in streaming side except for Apple everyone got the memo. (Outside of iOS), most non-Apple streaming services uses Opus if it's sensible (Dolby for surround sounds because patents and FLAC for lossless audio).

Can't upgrade before macOS and iOS get proper Opus support. Technically there is Opus support, but not to a degree where you'd actually want to start using it.

> Device support is good nowadays

Had some users with Opus issues on Android Oreo, it's getting there, but not ideal if you're targeting a global audience.

The current public test builds of Clone Hero, a fan-made Guitar Hero/Rock Band style game, support Opus audio alongside the legacy formats.

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