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Topic: m4a / AAC optimal encoding? (Read 1995 times) previous topic - next topic
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m4a / AAC optimal encoding?

I recently decided to upgrade my music from YouTube download mp3s to FLACs, which is great when I'm on my computer (at least in theory, my unrefined ears don't really hear a difference, but I'm sure there is one). However, FLAC is too big for my phone (Android), so I've been trying to figure out the best way to encode them. Originally, I wanted to do opus, but my music player (Blackplayer EX) doesn't play well with opus files. Specifically, the album-artist metadata tag doesn't work correctly, so if anyone happens to know a way to fix that, that'd be great.

From searching, it seems like AAC would be the next best option, correct me if I'm wrong. Currently, I'm using qaac to convert everything, using this command on Windows:

qaac64 <original>.flac -o <target>.m4a --tvbr 100 --copy-artwork

I keep trying to find the optimal settings to use, but it's really hard to find a consensus. I know tvbr defaults to 91 and ranges from 0-127, but I don't really understand the scale that that number represents. When I use 100, the bitrate ranges from 126-266, with an average around 220. Is this "transparent"? Transparent enough? Is there something better to use than qaac? Is there a better place to ask this? Any help is greatly appreciated, I'm very new to all this.

Re: m4a / AAC optimal encoding?

Reply #1 –
Quote
I recently decided to upgrade my music from YouTube download mp3s to FLACs,
Are you converting your MP3s or "downloading" again?

Converting to FLAC doesn't remove MP3 artifacts or add-back the missing information.    It's essentially the same as playing the MP3, but possibly worse because MP3 can go over 0dB and FLAC cannot, so there's the possibility of clipping.     (You'll also clip your DAC if you play the over-0dB MP3 at "full digital volume".)

Quote
From searching, it seems like AAC would be the next best option, correct me if I'm wrong. Currently, I'm using qaac to convert everything, using this command on Windows:
AAC is supposed to be better than MP3 at the same bitrate, if there is a difference.   Sometimes there is no difference.

But that's only if you start with an uncompressed original.    ANY lossy-to-lossy conversion introduces MORE quality loss.   (It may not sound different or worse, but it might.)

If someone uploads an MP3 to YouTube, it gets converted to the YouTube format.   If someone "downloads" and makes an MP3, it's been through 3 generations of lossy compression!!! 

Re: m4a / AAC optimal encoding?

Reply #2 –
Sorry, I should've been more clear, I redownloaded everything as a FLAC from Tidal

Re: m4a / AAC optimal encoding?

Reply #3 –
https://github.com/nu774/qaac/wiki/Encoder-configuration
The quality setting is just an arbitrarily set value for quality. The codec decides how much bandwidth it allocates based on the music.
Go as low as you can tolerate. Thats the ONLY advantage of lossy isnt it? Try it. I can guarantee you you will be surprised to how low you can go.
Notice how apple calls the 128 kbps setting high quality?

Re: m4a / AAC optimal encoding?

Reply #4 –
Code: [Select]
qaac.exe' -v 256 -q 2 *.flac

Produces a 100% transparent result (i.e. indistinguishable from FLAC) for me for 100% of tracks that I have.

Re: m4a / AAC optimal encoding?

Reply #5 –
I use qaac (in f2k) with the VBR Q 64 setting, which should be around 128kbps for stereo. I think that produces a very good quality and I doubt you'd hear artifacts during regular listening, that is, outside of focused AB testing. You could go a couple of notches higher to ~160kbps just to be safe, but we're at diminishing returns IMO.
Do a few ABX tests between VBR Q 64 and lossless and see if it's easy or not.

Re: m4a / AAC optimal encoding?

Reply #6 –
I think your on the right track since qaac defaults to 190 VBR
without parameters. I would think that apple knows something about
why it is the default.  220vbr would be an extra headroom
setting using this formula. Good setting IMO and less than 256/ 320 size.

Re: m4a / AAC optimal encoding?

Reply #7 –
Don't consider -V91 as sensible defaults. This value is not chosen by Apple by any means. It just happens to be this way.