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There are two quality parameters and I'm not sure which one is `-q` in afconvert. One of them is the VBR quality, `kAudioCodecPropertySoundQualityForVBR`. ffmp
by marcan_42 5y ago
There are two quality parameters and I'm not sure which one is `-q` in afconvert. One of them is the VBR quality, `kAudioCodecPropertySoundQualityForVBR`.
ffmpeg maps it like this:
q = 127 - q * 9;
So `-q:a 0` should do the same thing as passing 127 to AT.
There is another property though; an actual control of codec effort (`kAudioConverterCodecQuality`). That one should be accessible as `aac_at_quality` and maps 0 to 96, so there's no way to go up to the max of 127... But Apple defines "High" as 96, so I get the feeling there won't be a big difference between that and max, especially for an audio codec.
- Wowfunhappy 5y agoThank you, this is the best explanation I've gotten in years! > That one should be accessible as `aac_at_quality` and maps 0 to 96, so there's no way to go up to the max of 127. Is this a bug I should report to ffmpeg?
- marcan_42 5y agoIf there is a nontrivial file size or quality difference between those two settings, sure. If not, it's probably not worth it :)