Movie Essentials

Digital movies are represented by data streams that are manipulated to present a series of images (frames) at a rate designed to simulate motion. Audio can be synchronized by indices, by timing, by key frame reference or it may be embedded in the same stream with the video. The quality and size on disk of a particular movie can be manipulated by the selection of a compression codec and through specific parameters. The parameters for MPEG movies can be set within Fx MPEG Writer. The parameters for AVI movies are set through the interface provided by the codec manufacturer. See below for more.

Quality

Some AVI codecs have quality settings that might range from 0% to 100% or they may control quality by manipulation of the bit rate. MPEG movies have only two quality settings: Fast Encoding and Quality.

Bit Rate

Bit rate (or bitrate) is the average number of bits transmitted within one second of video or audio. The higher the bitrate the better quality.

MPEG-1 VCD requires a fixed (average) bitrate while MPEG-2 requires a variable bitrate wherein a minimum and maximum bitrate are selected.

Color Depth

The number of distinct colors that can be represented by a piece of hardware or software is called color depth or bit depth because it is directly related to the number of bits used for each pixel. For example 8 bits ( 2⁸) produces a color depth of 256 colors while 24-bit video has a color depth of (2²⁴) or about 16.7 million colors and  32-bit about 4.3 billion colors. To produce smaller movies the color depth can be reduced using a method called dithering which groups the available colors into cells which simulate the original color.

Frame Rate

The number of frames displayed per second determines the animation speed of your movie. The standard frame rate is determined by the color television standards NTSC and PAL. You can change the speed of motion (slow motion, fast motion) by varying the frame rate from the standard.

Key Frame

Key frames have no reference to the previous or next frame. Saving them too frequently can increase the file size because they don't use similarities between frames for additional compression. Setting them too far apart will slow down random access in the file and can result in very long delays when moving forward or backward through the media file.
 

Aspect Ratio

MPEG-1 and MPEG-2 interpret this value differently.

MPEG-1, the ratio refers to the width and height measured in pixels.

In MPEG-2, aspect ratio information refers to the overall display aspect ratio (e.g. 4:3, 16:9).