[Aqua-123]

Why

On NVIDIA GPUs, MP4 export keeps the NVENC engine at 100% and the CPU stages wait on it. Export uses preset p5. On screen recordings, p4 gives the same quality and file size and encodes about 1.65× faster.

What changed

• The export NVENC preset changes from p5 to p4. tune=hq, VBR, spatial and temporal AQ and b_ref_mode=middle stay the same. Recording settings are unchanged.

Tradeoffs

• p1–p3 are faster still, but at the same bitrate target they made 20–25% larger files on screen content without a VMAF gain. p4 is the fastest preset that keeps file size flat.

Blast Radius

Every NVENC export on Windows and Linux, plus render-farm workers that encode with NVENC. Only the encoder speed/quality trade changes. The bitrate, GOP and profile are the same, so players and uploads see the same kind of stream.

Verification

• cap export, RTX 3060 (driver 615.78), 5 alternating runs per side, all medians:
  • 4K60 screencast, 30 s: 23.9 s → 17.5 s (−27%)
  • 1080p60 screencast, 30 s: 6.55 s → 4.93 s (−25%)
  • 1080p60 high-motion test source, 60 s: 13.12 s → 9.65 s (−26%)
• Quality: VMAF against the source differs by 0.012 or less (for example 4K 98.93 → 98.92), and file size is within 2%.
• The ffmpeg preset sweep at Cap's Maximum, Social and Web bitrates gives the same result: p4 ≈ p5 VMAF (±0.05) at about 60% of the encode time.
• After the change NVENC still runs at 100%, so the encoder still limits export speed. The CPU frame copies are handled separately in perf(export): hand packed NV12 readbacks to the encoder without an extra AVFrame copy #2838 and perf(decoding): borrow FFmpeg decoded planes instead of copying #3249.
• cargo test -p cap-enc-ffmpeg: 224 passed.

Confidence Score: 5/5

This PR appears safe to merge.

Summary

Changes the NVENC export preset from p5 to p4.

• NVIDIA exports encode with a faster preset.

_{Reviews (1) · Last reviewed commit: "perf(export): encode NVENC exports with ..." · Reviewed by Greptile}

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