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