Video coder, decoder and transmission system

摘要

A picture coder decodes P frames without having to wait for the next I frame even if a data loss occurs, and ensures quick recovery from degraded picture quality. The picture coder, which controls updating of a reference picture based on a decoding status signal and a frame number sent from a picture decoder, uses an acknowledgment signal (ACK signal) as a decoding status signal. The picture coder has a decoding status determination module 109 which determines that a decoding error has occurred if the acknowledgment signal is not received within a specified time. The picture coder also has a reference frame updating module 110 for use when it is determined that a decoding error has occurred. The reference frame updating module 110 selects from pictures, which were received correctly before the decoding error occurred, one picture for use as the reference picture. This makes it possible for the picture coder to decode P frames without having to wait for the next I frame. <IMAGE>