Thread count and quality

YaBoyShredderson · 4th March 2021, 12:01

I use staxrip to encode and i usually use x264 high profile, crf 18, veryslow, film tune. I dont really mess with the other settings manually, except i set threads to 12. I have a 5900x and set it 12 because thats half my cpu, enabling me to still play games while encoding, or to run 2 encodes simultaneously, usually the latter.

From my understanding, x264 chooses 1.5x your logical thread count by default, i think this is to make sure your cpu is always fed with data, because some threads finish before others? So for me, thag would be 36 threads, which i was told can cause a noticeable degradation of quality. How much so and is it worth going even lower?

No matter how low i go in thread count, it would still take the same amount of time (in theory), because im always encoding many many files. Encoding the files back to back, or all at the same time isnt really relevant. While it would take much longer for any individual file to finish, the whole set would take the same amount of time.

Im not sure exactly about the amount of quality difference, but i would assume its not linear, so the difference between 1 thread and 6 isnt the same as 6 to 12, 12 to 18 etc, but what kind od bitrate savings can i expect? I use constant quality, so will the bitrate reduce at the same crf, or will the quality increase? So i can increase crf from 18 to 19 for example for same quality? Or will the file just be smaller staying with 18?

4th March 2021, 12:01	#1 \| Link
YaBoyShredderson Registered User Join Date: Jul 2020 Posts: 76	Thread count and quality I use staxrip to encode and i usually use x264 high profile, crf 18, veryslow, film tune. I dont really mess with the other settings manually, except i set threads to 12. I have a 5900x and set it 12 because thats half my cpu, enabling me to still play games while encoding, or to run 2 encodes simultaneously, usually the latter. From my understanding, x264 chooses 1.5x your logical thread count by default, i think this is to make sure your cpu is always fed with data, because some threads finish before others? So for me, thag would be 36 threads, which i was told can cause a noticeable degradation of quality. How much so and is it worth going even lower? No matter how low i go in thread count, it would still take the same amount of time (in theory), because im always encoding many many files. Encoding the files back to back, or all at the same time isnt really relevant. While it would take much longer for any individual file to finish, the whole set would take the same amount of time. Im not sure exactly about the amount of quality difference, but i would assume its not linear, so the difference between 1 thread and 6 isnt the same as 6 to 12, 12 to 18 etc, but what kind od bitrate savings can i expect? I use constant quality, so will the bitrate reduce at the same crf, or will the quality increase? So i can increase crf from 18 to 19 for example for same quality? Or will the file just be smaller staying with 18?