Video attributes

Tracks:

(in New Project menu only) sets the number of video tracks the new project is assigned. Tracks can be added or deleted later, but options are provided here for convenience.

Framerate:

sets the framerate of the video. The project framerate does not have to be the same as an individual media file frame rate that you load. Media is reframed to match the project framerate.

Canvas size:

sets the size of the video output . In addition, each track also has its own frame size. Initially, the New Project dialog creates video tracks whose size match the video output. The video track sizes can be changed later without changing the video output. We have: Project size = W×H pixels = canvas size = output size

Aspect ratio:

sets the aspect ratio; this aspect ratio refers to the screen aspect ratio. The aspect ratio is applied to the video output (canvas). It can be convenient to vary the size of the canvas in percentage terms, instead of having to calculate the number of W x H pixels. The aspect ratio can be different than the ratio that results from the formula: ${\dfrac{{h}}{{v}}}$ (the number of horizontal pixels divided into the number of vertical pixels). If the aspect ratio differs from the results of the formula above, your output will be in non-square pixels.

Auto aspect ratio:

if this option is checked, the Set Format dialog always recalculates the Aspect ratio setting based upon the given Canvas size. This ensures pixels are always square.

Color model:

the internal color space of CINELERRA-GG is X11 sRGB without color profile. CINELERRA-GG always switches to sRGB when applying filters or using the compositing engine. Different case for decoding/playback or encoding/output; the project will be stored in the color model video that is selected in the dropdown. Color model is important for video playback because video has the disadvantage of being slow compared to audio. Video is stored on disk in one colormodel, usually a YUV derivative. When played back, CINELERRA-GG decompresses it from the file format directly into the format of the output device. If effects are processed, the program decompresses the video into an intermediate colormodel first and then converts it to the format of the output device. The selection of an intermediate colormodel determines how fast and accurate the effects are. A list of the current colormodel choices follows.

RGB-8 bit: Allocates 8 bits for the R, G, and B channels and no alpha. This is normally used for uncompressed media with low dynamic range.
RGBA-8 bit: Allocates an alpha channel to the 8 bit RGB colormodel. It can be used for overlaying multiple tracks.
RGB-Float: Allocates a 32 bit float for the R, G, and B channels and no alpha. This is used for high dynamic range processing with no transparency.
RGBA-Float: This adds a 32 bit float for alpha to RGB-Float. It is used for high dynamic range processing with transparency. Or when we don't want to lose data during workflow, for example in color correction, key extraction and motion tracking.
YUV-8 bit: Allocates 8 bits for Y, U, and V. This is used for low dynamic range operations in which the media is compressed in the YUV color space. Most compressed media is in YUV and this derivative allows video to be processed fast with the least color degradation.
YUVA-8 bit: Allocates an alpha channel to the 8 bit YUV colormodel for transparency.

In order to do effects which involve alpha channels , a colormodel with an alpha channel must be selected. These are RGBA-8 bit, YUVA-8 bit, and RGBA-Float. The 4 channel colormodels are slower than 3 channel colormodels, with the slowest being RGBA-Float. Some effects, like fade, work around the need for alpha channels while other effects, like chromakey, require an alpha channel in order to be functional. So in order to get faster results, it is always a good idea to try the effect without alpha channels to see if it works before settling on an alpha channel and slowing it down.

When using compressed footage, YUV colormodels are usually faster than RGB colormodels . They also destroy fewer colors than RGB colormodels. If footage stored as JPEG or MPEG is processed many times in RGB, the colors will fade whereas they will not fade if processed in YUV. Years of working with high dynamic range footage has shown floating point RGB to be the best format for high dynamic range. 16 bit integers were used in the past and were too lossy and slow for the amount of improvement. RGB float does not destroy information when used with YUV source footage and also supports brightness above 100 %. Be aware that some effects, like Histogram, still clip above 100 % when in floating point. See also 17.3, 17.4 and A.3.

Interlace mode:

this is mostly obsolete in the modern digital age, but may be needed for older media such as that from broadcast TV. Interlacing uses two fields to create a frame. One field contains all odd-numbered lines in the image; the other contains all even-numbered lines. Interlaced fields are stored in alternating lines of interlaced source footage. The alternating lines missing on each output frame are interpolated.

The CINELERRA-GG Community, 2021
https://www.cinelerra-gg.org