ffmpeg -crf 0 -preset ultrafast -an参数

-crf 0: This sets the Constant Rate Factor (CRF) value to 0, which means lossless compression. This will result in a high-quality output file but also a large file size.

-preset ultrafast: This sets the encoding speed to ultrafast, which is the fastest encoding speed but may result in lower quality output.

-an: This disables audio encoding and saves only the video stream. This is useful if you only need the video portion of the file and want to save on file size.