Fix all-black H.264 output by avoiding lossless x264 in video handler - #23
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Generated videos played back as all-black in most players, browsers, and hardware decoders. ffprobe showed the cause: the stream advertised the "High 4:4:4 Predictive" profile while its pixels were actually yuv420p — a profile/chroma mismatch that breaks decoding. Root cause: ImageioVideoHandler.dump_to_fileobj forwarded the caller's `quality` to imageio-ffmpeg. At its top setting (quality=10, used for action rollouts) imageio-ffmpeg requests *lossless* x264, and lossless x264 is only available under the High 4:4:4 Predictive profile — so x264 stamped that profile even though the chroma stayed 4:2:0. Fix: encode with an explicit, finite CRF instead of imageio's quality knob. Append `-pix_fmt yuv420p -crf 18` to the ffmpeg output params, force `codec=libx264`, and drop the caller's `quality` so it cannot reintroduce lossless mode. The result is a standard "High" profile that plays everywhere at visually-lossless quality. Verified end-to-end: both quality=5 and quality=10 paths, plus a real action_forward_dynamics inference run, now produce profile=High / yuv420p. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Signed-off-by: Casper88tw <casper88tw@gmail.com>
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June 6, 2026 19:02
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Jun 7, 2026
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rahul-steiger-nv
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Jun 15, 2026
…NVIDIA#23) Generated videos played back as all-black in most players, browsers, and hardware decoders. ffprobe showed the cause: the stream advertised the "High 4:4:4 Predictive" profile while its pixels were actually yuv420p — a profile/chroma mismatch that breaks decoding. Root cause: ImageioVideoHandler.dump_to_fileobj forwarded the caller's `quality` to imageio-ffmpeg. At its top setting (quality=10, used for action rollouts) imageio-ffmpeg requests *lossless* x264, and lossless x264 is only available under the High 4:4:4 Predictive profile — so x264 stamped that profile even though the chroma stayed 4:2:0. Fix: encode with an explicit, finite CRF instead of imageio's quality knob. Append `-pix_fmt yuv420p -crf 18` to the ffmpeg output params, force `codec=libx264`, and drop the caller's `quality` so it cannot reintroduce lossless mode. The result is a standard "High" profile that plays everywhere at visually-lossless quality. Verified end-to-end: both quality=5 and quality=10 paths, plus a real action_forward_dynamics inference run, now produce profile=High / yuv420p. Signed-off-by: Casper88tw <casper88tw@gmail.com> Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com> Co-authored-by: Maosheng Liao <maoshengl@nvidia.com> Co-authored-by: lfengad <liangf@nvidia.com>
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Generated videos played back as all-black in most players, browsers, and hardware decoders. ffprobe showed the cause: the stream advertised the "High 4:4:4 Predictive" profile while its pixels were actually yuv420p — a profile/chroma mismatch that breaks decoding.
Root cause: ImageioVideoHandler.dump_to_fileobj forwarded the caller's
qualityto imageio-ffmpeg. At its top setting (quality=10, used for action rollouts) imageio-ffmpeg requests lossless x264, and lossless x264 is only available under the High 4:4:4 Predictive profile — so x264 stamped that profile even though the chroma stayed 4:2:0.Fix: encode with an explicit, finite CRF instead of imageio's quality knob. Append
-pix_fmt yuv420p -crf 18to the ffmpeg output params, forcecodec=libx264, and drop the caller'squalityso it cannot reintroduce lossless mode. The result is a standard "High" profile that plays everywhere at visually-lossless quality.Verified end-to-end: both quality=5 and quality=10 paths, plus a real action_forward_dynamics inference run, now produce profile=High / yuv420p.