How To Reduce CPU and Memory Usage in FFmpeg Video Recording

Video recording with FFmpeg can sometimes be a resource-intensive task, leading to high CPU and memory usage. However, there are several strategies you can use to minimize these demands and ensure your system runs smoothly. In this article, we’ll walk you through these methods in detail.

Using a Lossless RGB Output

One of the first steps you can take to reduce CPU usage is to use a lossless RGB output. This can help avoid the slow RGB to YUV conversion process. Here’s how you can do it:

ffmpeg -y -framerate 25 -video_size 1280x1024 -f x11grab -i :0.0 -c:v libx264rgb -crf 0 -preset ultrafast temp.mp4

In this command:

• -c:v libx264rgb instructs FFmpeg to use the libx264rgb codec, which avoids the slow RGB to YUV conversion.
• -crf 0 sets the Constant Rate Factor to 0, ensuring a lossless output.
• -preset ultrafast is the quickest encoding setting, which can help reduce CPU usage.

Re-encoding the Output

The lossless RGB output might be too large and incompatible with some players. Therefore, you might need to re-encode the output. Here’s a command you can use:

ffmpeg -i temp.mp4 -c:v libx264 -crf 23 -preset medium -vf format=yuv420p out.mp4

In this command:

• -c:v libx264 instructs FFmpeg to use the libx264 codec for re-encoding the video.
• -crf 23 is a reasonable value for the Constant Rate Factor, balancing quality and file size.
• -preset medium is a slower preset that provides better compression efficiency.
• -vf format=yuv420p ensures compatibility with a wider range of players by using a common pixel format.

Adjusting the Priority of the FFmpeg Process

You can also adjust the priority of the FFmpeg process to allocate less CPU time to it. This can be done using the nice command in the terminal:

nice -n 8 ffmpeg -y -r 15 -g 600 -s 1280x1024x24 -f x11grab -i :100 -vcodec libx264 /tmp/video.mov

In this command:

• nice -n 8 decreases the priority of the FFmpeg process. Higher values result in lower priority, freeing up CPU resources for other tasks.

Please note that lowering the priority of FFmpeg may reduce CPU usage but can also cause lags or dropped frames. It’s important to experiment with different priority values to find the right balance for your specific needs.

Controlling Memory Usage

Unfortunately, there is no direct way to limit the memory usage of FFmpeg as it is controlled by the kernel. However, you can explore cgroups and the kernel’s memory controller for more advanced memory management options. You can find more information on this topic in the Linux Kernel Documentation.

Conclusion

Reducing CPU and memory usage in FFmpeg video recording involves a combination of strategies, including using lossless RGB output, re-encoding the output, adjusting the process priority, and exploring advanced memory management options. By implementing these strategies, you can ensure smoother video recording with FFmpeg while minimizing system resource usage. Remember to adjust the command parameters according to your specific requirements and system capabilities.