[split-non-be] Align 0DOF ISAR bitrate at 256kbps to conform to BAP_48_6

• Related issues: #1086 (closed)
• Requested reviewers: @tyagiri

Reason why this change is needed

• The LC3plus codec can also be configured to be interoperable with LC3 coding as used in the Basic Audio Profile for Bluetooth Low Energy audio using the configurations 48_2, 48_4 and 48_6 as described in BAP Table 3.5. In this configuration the bandwidth is FB, high resolution mode is disabled and the frame duration is 10 ms.

Description of the change

• 48_6 compatible lc3plus frames can be generated by using the 256000 bps split rendering configuration as defined in Table 7.6 24. The Frame Data Length Request (FDLR) of the LC3plus payload must be in the range of FDLR1 (1 octet). Therefore the overhead of the LC3plus payload format amounts to 40 bits per split rendering frame. The LC3plus frame data block is followed by 40 bits of zero padding, to fill up the 2560 bits of the split rendering frame. This leaves 2480 bits for the LC3plus frame data block, which results in 1240 bits per LC3plus frame. This amounts to a LC3plus per channel bit rate of 124, which matches the 48_6 configuration defined in BAP Table 3.5.
• Short summary: LC3plus bitrate reduced to 2x124kbps from 2x126kbps to conform to BAP_48_6

Affected operating points

• 0 DOF split rendering at 256 kbps with LC3plus
• Bitstream non-BE, minor differences due to zero padding