set b_ref_mode=0 for ffmpeg NVENC encoder #2074
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Older NVIDIA cards (e.g. GTX 1650) don't support this feature, and ffmpeg somehow force-enabled it, despite docs saying it should be set to "auto", and --help saying the default is "disabled". Setting it to "disabled" in the encoder works around this issue. ALVR does not currently use multiple B frames, so there should be no difference and no obvious difference was visible when testing. The feature is documented as: "Using B frame as a reference improves subjective and objective encoded quality with no performance impact. Hence the users enabling multiple B frames are strongly recommended to enable this feature." Co-Authored-By: David Rosca <nowrep@gmail.com>
zmerp
approved these changes
Apr 17, 2024
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Older NVIDIA cards (e.g. GTX 1650) don't support this feature, and
ffmpeg somehow force-enabled it, despite docs saying it should be set to
"auto", and --help saying the default is "disabled". Setting it to
"disabled" in the encoder works around this issue.
ALVR does not currently use multiple B frames, so there should be no
difference and no obvious difference was visible when testing.
The feature is documented as:
"Using B frame as a reference improves subjective and objective encoded
quality with no performance impact. Hence the users enabling multiple B
frames are strongly recommended to enable this feature."
Wise man @nowrep said: "just disable it, it's ffmpeg or nvenc bug (it shouldn't explode on this not being supported when b-frames are not used)"
See #2064 for someone saying this workaround does work for them on an older card. I didn't notice anything different on a 3090 with 550 drivers and cuda 12.4.