HandBrake Low CPU Usage - HandBrake Not Using 100% CPU Cores

Reasons and solutions to HandBrake low CPU usage problems

"I'm re-encoding my video library into MKV containers and x265 codecs with HandBrake using an R710 w, 72 gigs of RAM, 2x Intel Xeon L5640 2.26GHz and six 7200 rpm hard-drives in a RaidZ2 configuration. My issue is that HandBrake only gets 20% utilization across the 12 physical cores/24 logical cores, whether the video is 480p, 720p 1080p or etc."

There are so many reasons why HandBrake does not use 100% CPU on your computer. It could be issues out of processor version and HandBrake video settings. Too many CPU cores and threads cause problem too. We'll give you a detailed analysis of those possible reasons. Also, you can find ideas helping tweak settings to up the utilization of CPU and make HandBrake convert content faster.

Why Is Processor Not Used Fully with HandBrake?

Reason 1. Quite possibly, the video encoding is as fast as it can be and there is no need to max out your CPU power.

New CPU comes with better architecture, tuned CPU scheduler and more cache. All this brings about a more energy efficient CPU resource allocation model. It is said that each new-gen CPU will be about 5-10% faster than the previous of last year, at the same clock speed. So HandBrake not using 100% CPU doesn't mean it runs slowly. Maybe the transcoding speed is the same as before or much faster.

Here is a comparison of HandBrake CPU usage on both i7-8700K and i5-3470 with exactly the same settings. The input source is a DVD of John Carter, while the output settings are x264, Fast 720p and frame rate same as source.

The picture below shows that HandBrake reaches up to 308 average fps with 75% CPU usage on i7-8700K while only 103 fps with 93% CPU usage on i5-3470. So you'd better measure the x264 performance by speed (fps) instead of CPU usage.

Reason 2. When encoding video, whether HandBrake can use all CPU cores or not is mainly depending on the codec selection. To be specific, HandBrake uses FFmpeg, libvpx and x265 as a backend. FFmpeg's multithreading ability relies on the codec.

• Algorithms of different codecs have a big effect on the capability of CPU utilization, especially the use of multi-cores and multi-threading. For example, VP9 has more decent support for multiple cores than x264/H.264.

• The new-version codec with algorithm revised might be more efficient than its old version, requiring less processing power.

Reason 3. HandBrake not using all cores might be caused by multi-cores or multi-threading. As we mentioned before, multi-threading capability is decided by codec, specifically, the algorithm of codec. So the results could be:

• When there are just a few CPU cores and logical processors, say 4 cores 4 threads, thread synchronization can be easily implemented by codec. Thus HandBrake CPU usage could be as high as 90% to 100%.

• When you have multi-cores and hyper-threading, say 6 cores 12 logical processor, it requires a really complicated codec algorithm to execute multiple cores and threads concurrently. It is likely to slow down a bit each time a CPU runs a different thread than before. The more cores and threads you have, the harder to synchronize them and the lower the CPU usage might be.

• But remember it is not certain that higher CPU usage will absolutely lead to faster video conversion. The encoding efficiency might be same, faster or slower in different CPU usage cases.

Reason 4. A special case for HandBrake low CPU usage is using it to rip a protected DVD. HandBrake can deal with some encrypted file after installing libdvdcss. But you will experience a long-time title scanning process, like 10 minutes. This Pass 1 step doesn't need to run CPU and the CPU usage is only 2%-3%. When it switches to Pass 2 encoding step, the CPU usage will soar to 90% or higher.

Reason 5. It is possible that constant updates make HandBrake get better at sharing CPU resources rather than hogging them. It may peg 100%, but when there are some other processes, your HandBrake CPU usage is going to be lower. So HandBrake not using all cores is not a problem.

Reason 6. The worst case is there is a hard limit on how much CPU resource can be used on a program. And 50% CPU usage really halve the encoding efficiency.

How to Make Full Use of CPU Cores/Threads to Speed up HandBrake

1. Download and install the latest version of HandBrake (1.2.0)
2. Try to use different codec, like H.264, H.265, etc or different video settings.
3. Avoid a few x264 options that do not support multi-threading, like --b-adapt 2.
4. Reflash the BIOS. Some people say it works. HandBrake CPU usage changes to 93%-97% after this operation, while 57%-65% before. Just have a try.
5. Try some other video transcoder software with the same source and settings, like WinX DVD Ripper.

FYI, HandBrake can maximally use 6 to 8 CPU cores with diminishing returns thereafter. See the details in https://handbrake.fr/docs/en/latest/technical/video-encoding-performance.html

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