Although the current state-of-the-art H.264
codec has become very mature with efficient
compression and low latency, the codec needs to
be further customized for video chat. The parameters
of a codec — frame rate, group of picture,
size, quantization parameter, and resolution —
need to be suited to the end system capabilities.
For example, two mobile devices with resolutions
x ¥ y (camera) and x1 ¥ y1 (display) in a
group video chat may decide on a common
shared resolution x2 ¥ y2 based on camera resolution
of mobile devices rather than using the
H.264 spatial scalability feature, which may
involve high latency.