When you play media files in Cinelerra, the media files have a certain number of tracks, a certain frame size, a certain sample size, and so on and so forth. No matter what attributes the media file has, it is played back according to the project attributes. So, if an audio file’s sample rate is different than the project attributes, it is resampled. In like fashion, if a video file’s frame size is different than the project attributes, the video is composited on a black frame, either cropped or bordered with black.
The project attributes are adjusted in Settings→Set Format and to a lesser extent in File→New. When you adjust project settings in File→New, a new, empty timeline is created. Every timeline created from this point on uses the same settings. When you adjust settings in Settings→Format, media on the timeline is left unchanged. Also, every timeline created from this point uses the same settings.
Set Format window
In addition to the traditional settings for sample rate, frame rate, frame size, Cinelerra uses some unusual settings like channel positions, color model, and aspect ratio.
Select an option from this menu to have all the project settings set to one of the known standards.
Sets the number of audio tracks for the new project. Tracks can be added or deleted later, but options are provided here for convenience.
Sets the samplerate of the audio. The project samplerate does not have to be the same as the media sample rate that you load. Media is resampled to match the project sample rate.
Sets the number of audio channels for the new project. The number of audio channels does not have to be the same as the number of tracks.
The currently enabled audio channels and their positions in the audio panning boxes in the track patchbay are displayed in the channel position widget.
The channel position widget
The channels are numbered. When rendered, the output from channel 1 is rendered to the first output track in the file or the first soundcard channel of the soundcard. Later channels are rendered to output tracks numbered consecutively.
The audio channel positions correspond to where in the panning widgets each of the audio outputs is located. The closer the panning position is to one of the audio outputs, the more signal that speaker gets. Click on a speaker icon and drag to change the audio channel location.
The speakers can be in any orientation. A different speaker arrangement is stored for every number of audio channels since normally you do not want the same speaker arrangement for different numbers of channels.
Channel positions is the only setting that does not affect the output necessarily. It is merely a convenience, so that when more than two channels are used, the pan controls on the timeline can distinguish between them. It has nothing to do with the actual arrangement of speakers.
Different channels can be positioned very close together to make them have the same output.
See section Panning audio tracks.
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.
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.
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. See section The track popup menu
Sets the aspect ratio. The aspect ratio is applied to the video output. The aspect ratio can be different than the ratio that results from the formula: 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 New Project dialog always recalculates the Aspect ratio setting based upon the given Canvas size. This ensures pixels are always square.
The project will be stored in the color model video intermediates selected in the dropdown.
Color model is very important for video playback because video has the disadvantage of being very slow. Although it is not noticeable, audio intermediates contain much more information than the audio on disk and the audio which is played. Audio always uses the highest bandwidth intermediate because it is fast.
Video intermediates must use the least amount of data for the required quality because it is slow, but video intermediates still use a higher bandwidth color model than video which is stored and video which is played. This allows more processing to be done with less destruction of the original data.
The video is stored on disk in one colormodel, usually a YUV derivative. When played back, Cinelerra decompresses it from the file format directly into the format of the output device. If effects are processed, Cinelerra 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.
Cinelerra colormodels are described using a certain packing order of components and a certain number of bits for each component. The packing order is printed on the left and the bit allocation is printed on the right.
This allocates 8 bits for the R, G, and B channels and no alpha. This is normally used for uncompressed media with low dynamic range.
This allocates an alpha channel to the 8 bit RGB colormodel. It is used for overlaying multiple tracks.
This 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 derivate allows video to be processed fast with the least color degradation.
This allocates an alpha channel to the 8 bit YUV colormodel for transparency.
This 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.
This adds a 32 bit float for alpha to RGB-Float. This is used for high dynamic range processing with transparency.
*In order to do effects which involve alpha channels, a colormodel with an alpha channel must be selected**. These are RGBA8888, YUVA8888, 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 to do anything, so it is 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 have 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.