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.