Advanced Options - Encoding Features
Advanced Options can result in poor performace or results if used incorrectly.
Force keyframe after ... delta frames
In normal operation the encoder will insert keyframes for scene changes or where a keyframe would result in a more efficient encode. But in order to promote random access it is sometimes necessary to insert keyframes more regularly. The codec will insert a keyframe if it has outputted this many non-keyframes in a row. By setting this value to 0 you can produce an all keyframe video, which could be usefull for an editing format, similar to DV. Keyframes are also usefull for streaming broadcasts, as a user can normally only begin watching a stream after receiving a keyframe, if the stream was 25fps, and keyframes were only inserted after 250 frames (worst case) then the user might have to wait 10 seconds before seeing the stream (worst case).
300 is the default value for normal video tasks, for streaming we recommend a keyframe every 5 seconds (fps times 5).
Speed vs Quality
- Half Pixel Motion
If checked the codec will perform half pixel precision motion search. Half Pixel motion dramatically increases quality and codec efficiency in almost all cases. Disabling Half Pixel Motion can speed up an encode.
- Four Vector Motion
If checked the codec will perform 8x8 block search as well as 16x16 block matching resulting in 4 motion vectors for some 16x16 blocks. This can improve the motion representation, thus improving quality and reducing bitrate. Disabling Four Vector Motion can speed up an encode.
Different Quantizers can be used when compressing video. The default Quantizer is the H.263 Quantizer, and results in good compression with a mild smoothing of the image. The MPEG-4 alternative Quantizer produces videos which are normally slightly sharper, but can exhibit blocking artifacts at high QPs and will normally require more bitrate. MPEG Quantization is not part of the Simple Profile and thus will force the output of Advanced Simple Profile video.
Advanced Simple Profile video in an MP4 file can not be opened by a Simple Profile Decoder, like QuickTime 6.
Custom Quantizer (ASP) is similar to the MPEG Quantizer except that custom Inter and Intra quantization matrices can be specified using the 'Customize Matrix...' button.
Custom Matrices are an expert setting and beyond the scope of this documentation. More...
When enabled 3ivx MPEG-4 5.0.1 generates video that is 100% ISO Pure MP4 compatible and will not work with some AVI based tools.
Pure MP4 is not required to be compatible with QuickTime 6 or 7's built-in MPEG-4 support.
NVop Coding is an Efficient method of coding dropped or duplicate frames. The effect is most noticable when enabled in low bitrate encodes. The NVop Coding Technique is MPEG-4 Compliant, however it is not supported by Apple's MPEG-4 Stream Hinter.
Quarter Pixel (QPel) motion compensation can increase effeciency by more precisely describing intra-frame motion. This is typically offset by the increased constant bitstream overhead of running a higher level of description. Therefore, enabling QPEL does not typically produce smaller file sizes. However, since QPEL delivers sharper images, an equivalent sized QPEL enabled file, will generally be perceived as offering higher visual quality, than a non QPEL file.
A feature which can dramatically improve the efficiency of the codec (resulting in smaller files which look better) by varying the quantization of the video on a block by block basis based on perceptual cues.
Adaptive Quantization works best with Constant Quality encoding to reduce the file size without dramatically reducing the quality. Adaptive Quantization also works well with Single Pass bitrate controlled encodes (CBR and ABR).
During a Dual Pass encode the Adaptive Quantization setting has no effect.
Selecting 'Bframes', turns on creation of Bframes during encoding. This can sometimes result in greater efficiency.