CPU advice needed for x265 encoding

General questions or discussion about HandBrake, Video and/or audio transcoding, trends etc.
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emmabux
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CPU advice needed for x265 encoding

Post by emmabux »

Hi,

Which CPU would be better/faster for x265 encoding with Handbrake, an Intel i3 7100/3.9GHz or i5 7400/3GHz? Both have HD 630 graphics.

A local retailer currently has a machine on sale with the option of a dual core i3 7100 or quad core i5 7400 CPU, with only a £5 difference in price. Both processors support QSV x265 encoding so it seems to be the choice of the i3 faster single thread performance Vs the i5 better multi thread performance, and I'm not sure which benefits Handbrake more.
I know these are low end processors, but I'll only use it occasionally to convert my DVD and BluRay collection over to x265 and for basic HTPC use.

Any advice would be much appreciated.
Woodstock
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Re: CPU advice needed for x265 encoding

Post by Woodstock »

Number of cores is important for encoding, if you're using x264 or x265. If you're using QSV, CPU cores are less important, but more is still better.
Deleted User 13735

Re: CPU advice needed for x265 encoding

Post by Deleted User 13735 »

I believe the number of cores/threads is important up to a point.
Six is kind of in a sweet spot, and I've seen tests from friends where encoding actually slows down past eight cores.
Last edited by Deleted User 13735 on Sun May 27, 2018 5:37 pm, edited 1 time in total.
Navvie
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Re: CPU advice needed for x265 encoding

Post by Navvie »

Tough question.

The i3-7100 has hyperthreading (2 cores, 4 threads), the i5-7400 doesn't (4 cores, 4 threads). A hyper-thread core isn't quite as useful as a 'real' core. However the extra clock speed of the i3 might negate this.

i5 has more cache, but runs at 3.0GHz flat, turbo upto 3.5GHz. The i3 is a flat 3.9GHz, no turbo.

I'd look at an i7 - 4 core, 8 threads in many models. Is it a small retailer where you can talk to them or a large box shifter? You'd have more luck talking the smaller retailer into changing the spec to an i7 and can talk about price difference with them.

It's worth noting that QSV transcoding doesn't use the normal CPU cores, but a separate, specific, QSV core. QSV output doesn't tend to match X264 or X265 quality wise, but the transcodes complete much faster.
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s55
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Re: CPU advice needed for x265 encoding

Post by s55 »

7400 will be better for video encoding. With more and more apps becoming heavily multi-threaded, you want to avoud dual core parts these days.

Hyperthreading is at best, around 20% increase. Even with the clock advantage, the i5 is probably ballpark 10~20% faster for the likes of HandBrake
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BradleyS
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Re: CPU advice needed for x265 encoding

Post by BradleyS »

Hyperthreading isn’t particularly faster for video encoding since most of the important code paths are fast assembly. Easy to demonstrate by temporarily turning off HT; the speed difference is usually negligible.

The 6-8 core ceiling mostly applies to x264. The x265 codec scales to many more cores.

Personally, I would find an i3 incredibly slow for any video encoding, and x265 is going to be dog slow. What s55 said, quad core is the minimum and you still might find it slow for x265.
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