Intra MB forcing using External QP-Table/LOAD_QP Mode - 2023.1 English

H.264/H.265 Video Codec Unit v1.2 Solutions LogiCORE IP Product Guide (PG252)

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2023.1 English

This forces specific blocks to be encoded in intra prediction mode. The bool AL_Encoder_Process (AL_HEncoder hEnc, AL_TBuffer* pFrame, AL_TBuffer* pQpTable) API forces Intra at block level and can be controlled with the QP table in the API. The QP table buffer must contain a byte per MB/CTB, in raster scan format:

  • In AVC, one byte per 16x16 MB
  • In HEVC, one byte per 32x32 CTB
  • The 6 LSBs of each byte are used for QP: absolute QP in [0;51] or relative QP in [-32;31]
  • The 2 MSBs are reserved for the prediction mode, as shown in the following table.
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Prediction mode QP
Table 1. Prediction Mode and Description
Prediction mode Description
0 Encoder free choice
1 Force Intra Prediction mode
2 Reserved
3 Reserved


  • To use force intra at block level, external QP tables must be enabled. Then, a QP table must be provided for each frame.
  • This feature is supported with RELATIVE_QP as well; Prediction mode and QP bit distribution remains the same as above.
  • This feature is also support with ROI_QP mode. The entire ROI region can be encoded with Intra MBs using the following quality option for the region:
    <quality> = INTRA_QUALITY