In my experience, an MP4 480p (or higher resolution) format will include a soundtrack that, when extracted without further changes will yield an approximately 125k m4a sound file. Similarly, an MP4 270/360p will yield a 96k m4a sound file.
Isn't it true that, aside from possibly better quality of the AO Opus Hi-Q format, everything else will be subject to the above limitations? In other words, you can resample a 125k file to 256k, but why would you want to? Perhaps I am mistaken.
Although I am talking about splitting hairs here, because the conversion from M4A (or an other lossy format) to MP3 involves expanding/un-compressing the source (in lossy formats) then re-compressing the source (into a different lossy format), there is some degradation each time it is done; ie "mistakes" get included which could also highlight the different/combined weaknesses between the two lossy formats. As such, doing it at a higher resolution would theoretically help minimise the effects.
If you were to take a high'ish freq sine wave (where a lot of lossy formats cheat you), compress it using M4A, then decompress the M4A back to raw data, then compress it using an MP3 algorithm, then uncompressed that to raw data then repeat the process many times, each time you do it your clean wave will degrade further (more distortion). ie you will loose some clarity, and hence M4A and MP3 are known as "lossy" formats. In simple terms, think of pouring water between two cups where you know you will loose a little water each time you do the exchange, eventually, your cups will be almost empty.
It seems the current best practice for obtaining highest quality audio from YouTube is:
Download MP4 480p (or higher resolution) format and extract audio without further encoding/modification.
Download AO Opus Hi-Q format
In my own experience, I haven't noticed any difference in sound quality between the two options, although I think the Opus might be a little more efficient, space-wise. Some media players don't support Opus, or have more difficulty keeping accurate track of time elapsed/remaining, especially when I skip around in a long Opus file.
Of course, none of the options provides really fine quality audio, but I have to admit that my 60-year-old ears don't notice the difference as much as they used to, and to have the vast range of audio and video materials available for review more than makes up for it in my opinion. The ability to download the files makes it much more convenient than relying on a live streaming connection, and so the developer of YTD really deserves our support! If I really like something, I will purchase a high-quality product (download/CD/DVD) from a commercial source.
I agree. But to keep the audio from the 480p format, just download the m4a... The 480p is a format handled via the app through FFmpeg: audio and video are downloaded separately and then mixed. You would do one unnecessary step otherwise. If you upload a 4K video with the exact codec settings they use to convert to, I *think* that *maybe* they do not transcode at least *that* format. Not sure I've been clear, sorry.
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