Shrinking — X265

To successfully compress an already efficient x265 file, one must understand how the encoder operates. The core of x265 efficiency lies in its use of Coding Tree Units, which allow for block sizes up to 64x64 pixels, far larger than the 16x16 macroblocks used in x264. This allows the encoder to compress large, uniform areas of a video frame, like a clear blue sky, with incredible efficiency. When your goal is to shrink these files even further, your primary tool is the Constant Rate Factor, or CRF. CRF is a encoding mode that adjusts the bitrate dynamically to maintain a consistent level of perceived visual quality. The CRF scale for x265 typically ranges from 0 to 51, where lower values yield higher quality and larger files, while higher values yield lower quality and smaller files. For x265, a CRF value between 20 and 24 is generally considered the sweet spot for balancing noticeable space savings against high visual fidelity. Moving a file from a default CRF of 20 to a CRF of 23 can often shrink the file size by thirty percent or more while remaining visually transparent to the casual observer during normal playback.

Their initial findings were perplexing. The files were indeed shrinking, but not in a uniform manner. Some files lost as much as 20% of their original size, while others remained relatively unchanged. The team suspected that the issue might be related to the encoding settings or the type of content being compressed. shrinking x265

ffmpeg -i input.mkv -c:v libx265 -crf 20 -preset slow -x265-params "aq-mode=3:psy-rd=1.5" -c:a copy output.mkv To successfully compress an already efficient x265 file,

"x265 looks soft and waxy"

The team's excitement was short-lived, as they realized that the shrinkage came at a cost. The reduced file sizes were achieved by discarding subtle details in the video, effectively reducing its overall quality. When your goal is to shrink these files