Dual Pass Encoding - 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

Encode the video twice; the first pass collects information about the sequence, and stats are used to improve the encoding of the second pass. The two levels are:

  • Real-time GOP/frame-level dual-pass < lookahead mode >
  • Offline sequence level dual-pass < two pass modes >

Until the 2019.1 release, only real-time GOP/Frame-level dual-pass is supported. IDR frames are automatically inserted based on first-pass scene change detection. The QP of each frame is adjusted based on internal stream size/complexity statistics/Scene change. Gop/Fame-level dualpass encoding is enabled by using "LookAhead" parameter at control-software and "look-ahead" at Gstramer.

Dual pass is not supported in the low latency mode.

Constraints: A maximum of 4kp30 is allowed in dual pass mode because the maximum VCU performance is 4kp60 and dual pass reduces the performance to half.

LookAhead = <value>

  • Default value is 0: Dual pass is disabled.
  • Above 2 (>=2): Scene change detection and correction.
  • Above 10: Constant quality, using frame complexity