When
YouTube first appeared on the scene, people were ecstatic and didn't really mind the poor quality. Now though, is a different story.
With the advancements we have made in the "speed" department of ISP's, better quality (and bigger file sizes) is here for us to enjoy!
Honestly, we have
H.264 codec to thank for this update. Without it, we wouldn't have HD, as it is supported as a encoding choice for Blu-ray and HD DVD movies. Now as for the audio, Flash now supports High Efficiency
AAC.