Not ideal, as you're recording a lossy format and re-encoding it through a lossy codec and you're also stuck with recording in realtime.

Not to mention that the chroma subsampling gets worse and worse this way. Not just because that's an inherent problem but also because youtube is (like most video players) horrendously bad at resampling the chroma.

This is sucks though. You end up wasting space to have a worse quality recording.