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MASA 2TC DTX to EXT output has transition artifacts

Basic info

Bug description

It seems that the fix for low bitrate MASA 2TC DTX in MR !668 (merged) introduced a bug in other bitrates of MASA 2TC DTX. This can be heard as transition artifacts when going in and out of DTX and using EXT output. The reason is that the copy condition in function ivas_masa_prerender() now applies to also SID bitrates which is correct if stereo core was operated in "one channel mode" but obviously wrong when operated in normal mode. As the left channel is copied to the right channel for the DTX periods, it is inevitable that discontinuities will happen which results in the artifacts.

As a side note, output of the DTX period to DirAC renderer may also have some gain difference as that is covered by the same condition.

Ways to reproduce

Encode 2TC MASA using DTX and bitrate higher than 16.4 kbps. Decode to EXT. Output transports will have the artifacts.