HomePage 5 of 8: x264 Options: Frame Options
Scene Cut:
Description: This option sets how x264 determines when a scene change has occurred and hence when a key frame is needed. A higher value will allow x264 to be more sensitive to scene changes. A video that has very few camera movements may require a higher scene cut value, for example. The default value of 40 should work well in most cases, plus or minus 5 for low/high action videos.
Command Line: --scenecut n
(where 'n' is the scene cut value)
CABAC:
Description: Stands for Context Adaptive Binary Arithmetic Coding. Improves encoding efficiency at the expense of playback/decoding efficiency. The default option of leaving this setting On is recommended, unless the encoded video is to be played back on devices with limited decoding power (eg. portable devices such as the iPod or high resolution clip playback on the Xbox).
Command Line: --no-cabac
(disables CABAC)
GOP Size (Min/Max):
Description: This option sets the minimum and maximum number of frames before a key frame has to be inserted by x264. For example, a minimum setting that is the same as the framerate of the video (eg. 24/25/30) will prevent the encoded video from having two subsequent key frames within a second of each other, which only aims to increase file size without any noticeable quality improvements.
Similarly, a maximum setting ensures that a key frame is inserted at least every X number of frames. A video without key frames will have lower quality and there will be problem with seeking (if you try to skip to a part of the video without a key frame, there won't be any video until the next key frame is reached, also known as "seeking lag"). A recommend setting, as with DivX/XviD encoding, is to set this as 10 times the framerate, which equates to 10 seconds of video between key frames (ensures "seeking lag" is at most 10 seconds).
Command Line: --keyint m --min-keyint n
(where 'm' and 'n' are the max and min GOP size values)
