Sometimes I'll find a really awesome song on YouTube but it will default to HD video playback which constantly buffers on my slow internet connection. All I care about is the audio quality, not the video quality, so can I lower the video quality to 240p without sacrificing audio quality?
Generally as the video quality, size, and codec is changed, the audio is also different that is used for that video data rate. The audios are often relative in size to the video. The amount of data used for the audio ranges from barely usable for music at all, to very nice, and varies depending on the video codec used and (of course) the audio codec.
There are charts on the Wikipedia page of YouTube which are mostly up to date, you could use that to find a balance.
Can you select a low video resolution, without sacrificing audio? For the most part: no, they aren't going to make tiny videos with audio data that is larger than the video. It also depends on more than the "resolution" as there are different methods used. Video codecs that are (more often) standardly used with specific audio codecs. Audio codecs that use different compression methods, and "sound good" at different data rates (ex vorbis).
Note that the bitrates below are recommendations for uploads. Audio playback bitrate is not related to video resolution.
So it seems audio quality is the same, irrespective of the selected video resolution. However, the audio quality will be as good (or bad) as the original video that was uploaded to YouTube.
Never mind my answer. @Psychogeek is right and YouTube does indeed change audio bitrates and codec. I'm not sure if it affects the perceived audio quality though.
You can find out what the current audio/video quality is by using the online YouTube video info tool. It'll list all the
itags for a YouTube video in addition to other information like bitrate (divide the listed number by 1000 to get the bitrate in kbps).
To find out the audio and video
itags for the video you're watching, right-click inside the player and select
Copy debug info and paste it into a text editor and search for
itag. Look up the
itag values and compare them to the output of YouTube video info tool. You can additionally, look them up on Wikipedia as well.
You can play a YouTube video in the lowest resolution setting and see what the audio stream
itag value is. If you find that it's fairly high (i.e. 251 or 141 for DASH, meaning 160 kbit/s or 256 kbit/s respectively) you can keep playing it at that quality level without worrying about sacrificing audio quality.