## Advanced Topics

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### Interlaced and field-based video

Currently (v2.5x and older versions), AviSynth has no interlaced flag which can be used for interlaced video. There is a field-based flag, but contrary to what you might expect, this flag is not related to interlaced video. In fact, all video (progressive or interlaced) is frame-based, unless you use AviSynth filters to change that. There are two filters who turn frame-based video into field-based video: SeparateFields and AssumeFieldBased. More information about this can be found here.

### Color format conversions, the Chroma Upsampling Error and the 4:2:0 Interlaced Chroma Problem

The Chroma Upsampling Error is the result of your video is upsampled incorrectly (interlaced YV12 upsampled as progressive or vice versa). Visually, it means that you will often see gaps on the top and bottom of colored objects and "ghost" lines floating above or below the objects. The 4:2:0 Interlaced Chroma Problem is the problem that 4:2:0 Interlaced itself is flawed. The cause is that frames which show both moving parts and static parts are upsampled using interlaced upsampling. This result in chroma problems which are visible on bright-colored diagonal edges (in the static parts of the frame). More about these issues can be found here.

### Colorspace Conversions

About the different RGB <-> YUV color conversions. <in progress>

### AviSynth, variable framerate (vfr) video and Hybrid video

There is two kinds of video when considering framerate. Constant framerate (cfr) video and variable framerate (vfr) video. For cfr video the frames have a constant duration, and for vfr video the frames have a non-constant duration. Many editing programs (including VirtualDub and AviSynth) assume that the video has cfr. One of the reasons is that avi doesn't support vfr. This won't change in the near future for various reasons. Although the avi container doesn't support vfr, there are several contains (mkv, mp4 and wmv for example) which do support vfr.

It's important to realize that in general video is intrinsic cfr (at least in the capping video or ripping dvds arena). There is one exception where converting to vfr is very useful, which is hybrid video. Hybrid video consists of parts which are interlaced/progressive NTSC (29.97 fps) and FILM (which is telecined to 29.97 fps). When playing hybrid video the NTSC part (also called video part) is played back at 29.97 fps and the telecined part at 23.976 fps. Examples of hybrid video include some of the anime and Star Trek stuff.

More info about creating vfr video and opening it in AviSynth can be found here.

### Luma-range, codecs and AviSynth

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http://forum.doom9.org/showthread.php?s=&threadid=83681

### Resizing

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`$Date: 2005/10/03 16:31:31 $`