Picture resolution in a CIF picture is 352 x 288 pixels. Audio, on the other hand, has three modes of compression. Usually, G.728 is used only during low-bandwidth teleconferencing calls. If the transmitting end sends a QCIF picture with G.728 audio to another system, the lowest common denominator takes precedence. Available bandwidth and the quality of video and audio encoding and decoding also impact teleconferencing results.
Video is a very complex signal.
On your TV set at home, you watch a picture that changes every 30 frames per second. You've probably noticed that old-time silent movies move in a jerky fashion. Depending upon the transmission data rate, the frames per second vary from a few per second to 30 frames. Basically, the encoding process looks at each frame, tries to determine what is moving, and then encodes that motion. It sends only the information that has changed since the prior frame.