A multimedia decoder unit having error concealment and fast muting capabilities.
The audio decoder provides error concealment using a dynamic recovery delay that
is based on the error rate of an input digital bitstream and also uses frame repeating.
The decoder allows fast audio muting whereby audio can be muted within two audio
frames of a mute signal that immediately freezes the video frame, e.g., a channel
change. With respect to the dynamic recovery delay, a template of fixed length
is used to inspect the last frames within the template. If error is found, then
the error sum is used as an index into a table length which provides a dynamic
template length. Error within the dynamic template length is computed and if larger
than a tolerance, the current frame is muted. This allows the recovery delay to
be adaptive and based on the error rate while still allowing mute merging. Muting
the current frame can be achieved by repeating the previous frame but the delay
data of the last block of the previous audio frame is added to the first block
of the repeated audio frame to provide a smooth frame interface. In response to
a mute command, the decoder zeros the audio output bitstream stream to provide
zero frames at the audio output buffer (AOB). In addition, the decoder also directly
zeros audio frames in the AOB that lie between its the read and write pointers
to guarantee that only two frames of audio be played after the mute signal.
