Finally got my answer about Youtube’s audio specification — there isn’t one, really.
The only have a video policy. Audio stream quality is a part of the video spec.
So here’s the details:
- Audio streams as 128k or 320k MP3 only
- 320k is only played during videos streaming in HD of 720p or higher
- The video must start in HD to get the 320k audio, and most players will not reload the higher audio stream if the user switches video quality during playback.
The end result is that most of youtube is streaming 128k mp3 audio, aka garbage.
The high quality portion of youtube can get 320k MP3 to you but it’s not automatic. They have to force the player into high-quality, which is against the youtube platform defaults.
The FLAC folks on Youtube? They force the 320k MP3 and perhaps they are encoding the video with a high resolution flac as the audio source? Or they are just misrepresenting themselves?
The two I contacted about their sources never answered me, so I don’t know. From what I’ve read youtube cannot stream FLAC or even lossless audio.
And yes, 320k MP3 sounds pretty good, it’s almost CD quality. But there’s still digital loss, artifacts, and a fatigue from listening.
CD’s usually push about 800k bitrate at you, so the perceptual coding at 320k sounds pretty close to the original.
But once you up that lossless original to between 2000-6000k (24bit audio) you really hear it pop and become realistic as compared to 320k.
Here’s to hoping youtube allows lossless streaming soon, or at least defaults to 320k mp3.