Allow more control over playoutDelay behavior

[murillo128]

After have tried to make the current playoutDelay extension to work in chrome, I found several usability issues that prevent it from being usable (at least from my point of view and others on the discuss-webrtc mailing list).

I think that it would be very interesting to allow more control on how the playoutDelay is applied by the browser. IMHO this would require to add to new attributes:

• playoutDelayMin which specifies the minimum value allowed for the actual playout delay applied by the browser. In case that the current delay is lower than the min one, the browser must insert silence or no audio/video be played until the min delay is reached.
• playoutDelayMax which specifies the maximum value allowed for the the actual playout delay applied by the browser. In case that the current delay is bigger than the maximum value, the browser will drop frames until the max playout delay is reached.

When the playout delay is between the min/max values, the browser should accelerate/decelerate the media playout until the playoutDelay is reached.

Each browser would be able to specify a different range for the allowed min/max values and the default values.

[AndrewJDR]

The min/max provides an immediacy of effect and overall predictability in behavior that seems important to make the playoutDelay extension more useful.