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Appendix
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Appendix

Rate Control Settings

H.264 Advanced Settings

[Bitrate]   [Quantization Limits]   [Scene cuts]


The Bitrate section comprises the following codec parameters:

  • Keyframe boost controls how much the quality of key frames (I-frames) is boosted as compared to the other frames (P-frames). Please, see the B-VOPs section of the MPEG-4 codec for more detail on different frame types used in video coding. The boost gives I-frames some extra quality, so frames predicted from them will also be of better quality, leading to a better visual impression. The higher the value, the more quality is given to the I-frames and the less to the other frames. You can try the higher values for low-bitrate and low-quality encodes or lower values for bright, continuously fast-moving videos where the background is frequently changing. The possible values vary from 0 to 70. The default value is 40.

  • B-frames reduction controls how much the quality of B-frames is reduced as compared to the other frames (P-frames). This cut in B-frame bitrate is hardly noticeable to the human visual system because B-frames are used inconspicuously in between other frames to more efficiently recreate the video's motion. It is possible to lower this value a little for high-bitrate/low-quantizer video thereby ensuring a more uniform quality to details, motion and the video as a whole. For animated content (cartoons, anime), you might use higher values. The possible values vary from 0 to 60. The default value is 30.

  • Bitrate Variability controls the extent to which the codec can variate the quality throughout the movie at the bitrate specified. The lower this option is set, the more unstable and erratic the quality changes can become. The higher this setting is, the more equal the quality becomes, producing a video with more stable quality. The possible values vary from 0 to 100. The default value is 60.

All the Bitrate settings can be altered manually to suit your personal needs - you can enter the values using the keyboard or with the mouse clicks.

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The Quantization Limits section comprises the following codec parameters:

  • Min QP sets the lowest quantizer your video can attain at any point. Very high values are not recommended unless you plan video with an immensely high bitrate and low resolution. The possible values vary from 0 to 51. The default value is 10.

  • Max QP sets the highest quantizer you video can reach. It is strongly recommended leaving it where at the default value of 51. The possible values vary from 0 to 51. The default value is 51.

  • Max QP Step controls how how much the quantizer can change between two consecutive frames. Setting this value too low forces the codec to switch quality levels slowly, which can be devastating to the compression of certain scenes which, for example, could suddenly use a lower quantizer to maintain similar visual quality. Setting it too high can lead to conspicuous jumps in quality. The possible values vary from 0 to 50. The default value is 4.

All the Quantization Limits settings can be altered manually to suit your personal needs - you can enter the values using the keyboard or with the mouse clicks.

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The Scene cuts section comprises the following codec parameters:

  • Scene Cut Threshold determines how much a frame needs to change before being considered a scene change by the codec. The higher the value, the less sensitive scene change detection will be. For dark videos you might want to decrease this value so as to let the codec more accurately determine scene changes. As a more general rule, videos with more subtle scene changes need a higher scene cut threshold and bright high-contrast videos with very prominent scene changes might actually be reason to attempt to set a lower threshold. The possible values vary from 0 to 100. The default value is 40.

  • Min IDR-frame interval sets the minimum number of frames between two keyframes. If this value is set too high, too much time will go by without the codec detecting a scene change and implementing the necessary keyframe. Setting it too low can result in a waste of bitrate and sometimes flickering. The possible values vary from 0 to 100000. The default value is 25.

  • Max IDR-frame interval sets the maximum distance between two keyframes. Setting this too low can result in an oversaturation of key frames, possible flickering, and general bitrate waste, reducing overall quality. Setting this too high can result in seeking issues, and any artifacts/encoding flaws during the time between key frames will remain on the screen longer. The possible values vary from 0 to 100000. The default value is 250.

All the Scene cuts settings can be altered manually to suit your personal needs - you can enter the values using the keyboard or with the mouse clicks.

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If you are not sure which settings to use you can press the Restore Defaults button to discard the changes and restore default settings.

When ready press the OK button to accept the changes you have made.

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