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Technical Committee on Human Factors - Guidelines for real-time communication services
 
 
 
 
 

 Lip-synchrony/asynchrony

 
 
 
 
 
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Frequently asked questions

  1. What is the Asynchrony if the audio delay is 100ms and video delay is 50ms?
  2. What is the Asynchrony if the audio delay is 100ms and video delay is 400ms?
  3. Are there cases where immediate audio transmission should be considered instead of synchrony?
  4. Is asynchrony only concerned with an aim for lip-synchrony?
  5. Is it possible to have a high Framerate but high video delay?

1. What is the Asynchrony if the audio delay is 100ms and video delay is 50ms?

<Asynchrony> = <Audio delay> – <Video delay> Asynchrony = 100 ms – 50 ms = 50 ms

2. What is the Asynchrony if the audio delay is 100ms and video delay is 400ms?

<Asynchrony> = <Audio delay> – <Video delay> Asynchrony = 100 ms – 400 ms = – 300 ms

3. Are there cases where immediate audio transmission should be considered instead of synchrony?

Yes, when delay is very long.

4. Is asynchrony only concerned with an aim for lip-synchrony?

No. Asynchrony concerns all situations where the sound source is presented on video, especially when it is distinct sound like when hands are clapping, pen falling to a table or slamming of a door.

5. Is it possible to have a high Framerate but high video delay?

Yes. A good codec used on a network with long delay, like a satellite connection, will be an example in this case.