Accept 'auto' in num_ffmpeg_threads #541

Job	Run time
generate-matrix / generate	4s
Build and Upload wheel / manywheel-py3_9-cuda11_8	6m 38s
Build and Upload wheel / manywheel-py3_9-cuda12_4	6m 57s
Build and Upload wheel / manywheel-py3_9-cuda12_6	7m 11s
Build and Upload wheel / upload / manywheel-py3_9-cuda11_8	16s
Build and Upload wheel / upload / manywheel-py3_9-cuda12_4	25s
Build and Upload wheel / upload / manywheel-py3_9-cuda12_6	17s
install-and-test (3.9, 11.8, 5)	3m 16s
install-and-test (3.9, 11.8, 6)	3m 15s
install-and-test (3.9, 11.8, 7)	3m 13s
install-and-test (3.9, 12.1, 5)	3m 17s
install-and-test (3.9, 12.1, 6)	3m 13s
install-and-test (3.9, 12.1, 7)	3m 23s
install-and-test (3.9, 12.4, 5)	3m 27s
install-and-test (3.9, 12.4, 6)	3m 16s
install-and-test (3.9, 12.4, 7)	3m 26s
	51m 34s

Provide feedback