Hi While encoding a video file using FFmpeg we have option to handle thread parameter. I used Quad Core Processor and find below my observations.
*Case 1: Default thread usage* By default if we didn't specify thread value FFmpeg internally adjusts thread count usage based on the core architecture of the deployment machine. Example: ffmpeg -i football_1080p.mp4 -c:v libx264 -b:v 3M -bufsize 6M -maxrate 4.5M -g 120 -tune psnr -report football_1080p_3M_threads_1_p.mp4 If I repeat this command n times for encoding always the encoded file size is similar in all iterations. *Case 2: Manually forced thread count usage* * Example 1: Thread count 1* ffmpeg -i football_1080p.mp4 -c:v libx264 -b:v 3M -bufsize 6M -maxrate 4.5M -*threads 1* -g 120 -tune psnr -report football_1080p_3M_threads_1_p.mp4 *Example 2: Thread count 6* ffmpeg -i football_1080p.mp4 -c:v libx264 -b:v 3M -bufsize 6M -maxrate 4.5M -*threads 6* -g 120 -tune psnr -report football_1080p_3M_threads_1_p.mp4 *Example 3: Thread count 9* ffmpeg -i football_1080p.mp4 -c:v libx264 -b:v 3M -bufsize 6M -maxrate 4.5M -*threads 9* -g 120 -tune psnr -report football_1080p_3M_threads_1_p.mp4 *Example 4: Thread count 20* ffmpeg -i football_1080p.mp4 -c:v libx264 -b:v 3M -bufsize 6M -maxrate 4.5M -*threads 20* -g 120 -tune psnr -report football_1080p_3M_threads_1_p.mp4 If I repeat this command 4 times for encoding the encoded file size differs with few KB in all iterations. Why is this difference ? That implies that if I put the thread count at 0 on two different machine architectures, I will again get two different output file sizes for the same thread count (0, in this case) and same input file. Also I am curious to know the below mentioned quires 1. What does the threads command do? 2. What does FFmpeg do if you don’t specify a threads value? 3. How does the threads settings impact performance? 4. How does the threads setting impact quality? Please clarify. Regards Anand V _______________________________________________ ffmpeg-user mailing list [email protected] https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
