One of the most fundamental encoding decisions is the size of the Group of Pictures (GOP) or the frequency of I-frames within an encoded file. I-frames, also known as keyframes, are the starting points for groups of pictures, consisting of I-, B-, and P-frames. Traditionally, the GOP size is directed by adaptive bitrate streaming considerations, such as ensuring an I-frame …

Here are three things to know about 2-pass x265 encoding with FFmpeg.  If you’re using -pass 1 and -pass 2 in your command string, it’s probably not working. You must use x265-params 0:pass=1 and then x265-params 0:pass=2 in the second pass. In the way we absolutely love about FFmpeg, there’s no error message if you use -pass 1/-pass 2; it …

I’m running some 1-pass vs. 2-pass comparison testing with x265. Unlike with x264 (see tests here), there’s a substantial performance penalty for running 2-pass with minimal quality benefit. I tried the no-slow-firstpass=1 setting, which only accelerated two-pass by about 14%. Here are the results from a single test file. I don’t want to process them all if there’s a magic …