4.5 Video Preference

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If a host decides that it would like to change the video resolution it is receiving, it does the following:

Message exchange for video preference

Figure 11: Message exchange for video preference

On receipt of the RTP video packet at Common Intermediate Format (CIF) resolution, Host2 decides to request the next video packets at VGA resolution. Host2 sends an RTCP packet with a video preference extension. Upon receiving this preference, Host1 asks the encoder to generate an I-frame at the preferred resolution to be sent to Host2. The encoder can decide to ignore this request if it cannot honor this video resolution. Reasons that the encoder cannot honor this request include:

  • The bandwidth is not sufficient.

  • The camera does not support the resolution.

  • The computer is not powerful enough to honor this request.

  • The resolution was not negotiated in video capability negotiation.

If the encoder can honor this request, the next subsequent video packets contain the I-frame of the new resolution.