How to reduce cpu usage of ffmpeg?

When using ffmpeg for video processing, reducing CPU usage typically involves finding a balance between performance, speed, and output quality. Below are some methods to reduce ffmpeg's CPU usage:

1. Use Less Encoding Compression:

   • Reduce the output video bitrate using the -b:v parameter (video bitrate).
   • Select a lower video quality preset. For example, with the x264 encoder, -preset ultrafast is faster than -preset medium, but may result in larger file sizes and lower quality.

2. Lower the Resolution:

   • Reducing the output video resolution can significantly reduce the CPU resources required for encoding. Use the -s option to set the resolution, e.g., -s 1280x720.

3. Lower the Frame Rate:

   • Lowering the video frame rate can reduce the CPU load. Use the -r option to set the frame rate, e.g., -r 24 sets the frame rate to 24 frames per second.

4. Use Hardware Acceleration:

   • If your system supports hardware acceleration, you can leverage the GPU for video encoding and decoding to alleviate the CPU load. For example, with NVIDIA hardware acceleration, use -hwaccel cuvid -c:v h264_nvenc (depending on the specific video codec and hardware).

5. Optimize Thread Usage:

   • Control the number of threads used by ffmpeg. Use the -threads parameter to limit the number of threads. For multi-core processors, ffmpeg defaults to using all available cores, but reducing the thread count may help lower the overall CPU load in some cases.

6. Avoid Unnecessary Filtering and Processing:

   • Avoid using complex filters and transition effects if not necessary, as they increase CPU workload.

7. Prioritize Lighter Encoders:

   • Choose an encoder with lower CPU usage, such as mpeg4, which may use fewer CPU resources than h264 but could sacrifice compression efficiency and quality.

8. Batch Processing and Scheduling:

   • Perform batch encoding during periods of low system load and consider setting a lower priority so that ffmpeg does not consume excessive CPU resources, affecting other critical system operations.

Example: Suppose you need to transcode a high-definition video to standard-definition while minimizing CPU usage:

shell
ffmpeg -i input.mp4 -c:v libx264 -preset ultrafast -b:v 1000k -s 640x480 -c:a copy -threads 2 output.mp4

In this command, I used the libx264 encoder, set -preset ultrafast to reduce CPU usage, limited the video bitrate to 1000k to reduce file size, lowered the resolution to 640x480, and limited the number of threads used by ffmpeg to 2. The audio stream uses the copy parameter to directly copy without re-encoding, further reducing CPU load.