Add a warning when streaming at >1x

[insidegui]

We've had many issues reported before about playback glitches when streaming at speeds higher than 1x. We've tried many workarounds and it seems to be an issue with AVFoundation which we can't do anything about (other than filing radars).

I proposed that we add a warning the first time a user tries to stream a video at higher speeds suggesting that they download the video instead of streaming, otherwise we'll keep getting repeated issues opened for this.

[PaulSolt]

Thank you! A warning is a great idea.

[insidegui]

TODO: Check if addressing #465 has an effect on this issue.

[dinesharjani]

Is this fixed? I'm asking because #465 has been closed and these two issues are marked as related.

[allenhumphreys]

I think we’re holding off to get feedback on whether the related issues addressed the underlying problem here.

[dinesharjani]

Got it. Thanks!