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Old 20th September 2019
  #29
Here for the gear
 
Apologies for being a nobody popping out of nowhere, but as a digital audiophile and enthusiast that's a regular of the Doom9 forums who also regularly uses youtube-dl, I'd like to clear up a few things...


1. All except the lowest of least popular videos and/or super-recent video uploads will receive audio encodes in both AAC and Opus with a bitrate of roughly 128kbps (the Opus encodes tend to commonly hit considerably higher bitrates however).

2. YouTube's AAC audio encodes use a sampling rate of 44.1KHz while their Opus audio encodes use a sampling rate of 48KHz (for one, Opus doesn't even support 44.1KHz)

3. YouTube always defaults to playing with Opus audio is the encodes exist and your browser supports it (AFAIK Safari is the only modern big-name browser that does not support Opus audio)

4. For a given sampling rate and bit rate, Opus should almost if not always be considerably higher quality than AAC

5. You will only ever find 192kbps AAC audio on YouTube'd non-DASH fmt22 encodes on old and/or unpopular videos. In general, if the video also has VP9 video encodes and/or Opus audio encodes, then the AAC audio for the non-DASH fmt22 encode will be at 128kbps (however, I do believe that more recent unpopular videos without VP9 and Opus encodes will still have only 128kbps AAC audio for their non-DASH fmt22 encodes).

6. YouTube supports the MKV video container, so you can very easily combine traditional video formats (AVC, VP9, etc) with a variety of lossless audio codecs (most notably 24bit FLAC) that aren't supported by other common video container formats (e.g. MP4, MOV, WebM, etc).