ISM Extended Metadata Clicks in case of Bitrate Switching

ISM extended metadata is supported for bitrates higher than 64kbps. For the bitrates lower than 64kbps, the additional metadata parameters are set to default. During bitrate switching, this causes clicks during the transition between default and actual extended metadata parameters.

One example is shown for the following case where the radius in the extended metadata file is higher than the default value, 1.0f:

./IVAS_cod.exe -ism +1 md4.csv ./switchPaths/sw_13k2_to_128k_10fr.bin 48 testv/stv1ISM48s.wav bit

./IVAS_dec.exe BINAURAL 48 bit out.wav

Proposed solution is a simple linear interpolation of the gain to avoid abrupt changes. Resulting output for the same parameters is then: