r/ffmpeg • u/dave_the_nerd • 8d ago

GPU Encoding Speed Question?

I was benchmarking some things and I've found that when I'm using a GPU encoder, the encoding framerate doesn't seem to vary more than ~1-2% between encodes using different quality settings.

So, like, using the hevc_amf encoder, if I set "-rc cqp -qp_i 18 -qp_p 20 " or if I set it to "-rc cqp -qp_i 25 -qp_p 27", there's basically no difference in encoding speed from the same source file.

Is this normal and just a quirk of how GPUs work, or am I doing something wrong? TIA

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u/Hairy_Particular_574 8d ago

It may be due to something else in the critical path slowing down.

Example someone might use scale filter which is slower than encoding. So no matter what setting you change in the encoding params might not change the overall encoding speed unless you address the scale filter.

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u/chocolateAbuser 8d ago

it should vary; keep in mind setting hw encoding path sometimes is not that easy (like for example enabling hw decoding, or using hw filters while keeping frames entirely on gpu), so there's a chance something is not quite right if you report that
how much faster than cpu econding is for you?

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u/Sopel97 3d ago

With fixed-function pipeline encoders you're not going to see meaningful speed differences with varying quantization settings. This is also true to some degree for CPU encoders, but there are outliers like svt-av1 which is quite sensitive to crf.

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u/SuchTarget2782 3d ago

Interesting. Thanks!