It also may slow down the first pass of x264 when in threaded mode. Its speed gets considerably slower at high bframes values, so its recommended to keep bframes relatively low (perhaps around 3) when using this option. A good balance between speed and quality.Ģ: A much slower but more accurate B-frame decision mode that correctly detects fades and generally gives considerably better quality. Does not work with pre-scenecut (scenecut must be off to force off b-adapt).ġ: Fast, default mode in x264. Recommended default: 1Ġ: Very fast, but not recommended. It is possible to disable this adaptivity this is not recommended. X264, by default, adaptively decides through a low-resolution lookahead the best number of B-frames to use. Note that Baseline Profile, such as that used by iPods, does not support B-frames. This parameter simply serves to limit the max number of B-frames. Most, however, do not as a result, there is rarely any negative effect to setting this to the maximum (16) since x264 will, if B-adapt is used, automatically choose the best number of B-frames anyways. Some specific targets, such as HD-DVD and Blu-Ray, have limitations on the number of consecutive B-frames. This is not compatible with threading, however, and so -pre-scenecut is automatically activated when multiple encoding threads are used.ī-frames are a core element of H.264 and are more efficient in H.264 than any previous standard. Normal scenecut detection decides whether a frame is a scenecut after the frame is encoded, and if so then re-encodes the frame as an I-frame. Slightly faster (but less precise) scenecut detection. Recommended default: 25Īdjusts the sensitivity of x264's scenecut detection. Minimum GOP length, the minimum distance between I-frames. Very high GOP lengths will result in slightly more efficient compression, but will make seeking in the video somewhat more difficult. This determines the maximum distance between I-frames. Keyframe interval, also known as GOP length. This guide maps most of x264's options to FFmpeg's options along with detailed descriptions by x264 developer Dark_Shikari.

Please see `avconv -h | less` or `ffmpeg -h | less` and scroll down to ' libx264 AVOptions:'.

Please Note: This guide will remain here for historic purposes but FFmpeg and libav now use libx264's internal -preset, -profile and -tune options.

Ffmpeg libx264