The `amf_xxx_update()` functions for AVC, HEVC, and AV1 are
unconditionally invoking Flush() and ReInit() even though this is not
required in all situations. Changing the bitrate at least in CBR mode
does not require the flush operation and can result in unaligned IDR
frames across members of an encoder group. Do not flush the pipeline
for CBR bitrate changes; instead, force an IDR to occur with the
bitrate change.
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