QuickTime format use a compression codec (compressor/decompressor), an algorithm that reduces file size by removing less important or duplicate information. Some codecs compress spatially. This means in an area of flat color (like a sky or sea), rather than recording all of the individual identical pixels, the codec treats the area as one unit. Other codecs compress temporally by examining a series of frames, recognizing the differences between them, and recording only that information.


You to should choose the value of your movies in five areas: codec, image size, frame rate, data rate, and audio compressor.


Codec: The Expert option offers a daunting range of codecs, from industry standard to downright esoteric. However, 99 percent of you need only Sorenson, a temporal compressor, and Cinepak, a spatial compressor. The Sorenson video codec produces excellent Web and CD-ROM video that any Pentium or PowerMac can download and play, provided it has QuickTime 3.0 or later. Compared with Cinepak, Sorenson generally achieves higher image quality at a smaller file size. However, it greater processing power, so if your movie will be viewed with older computers that can't download QuickTime 3 and 4 - as unlikely as that may be - you should probably compress in Cinepak.


Don't let the daunting list intimidate you. Stick with small Sorenson or Cinepak, and you’ll be just fine.


Frame Rate: A frame is a still image, and frame rate is the number of per second (fps) in your movie. North American video standards for 30 fps (actually 29.97 fps, to be persnickety.) A Web movie can get by with 7.5 to 10 fps. An action video requires a higher frame rate than a still interview.



Other Video Compression Coding



The Joint Photographic Experts Group (JPEG) defines a set of compression for single pictures. It is based on a lossy compression and reaches a ratio of 1:10 with a fair quality. It also uses the run-length and Hoffman compression algorithms. JPEG can be used for video sequences by compressing all frames. This is called Motion-JPEG (M-JPEG) and ignores temporal redundancy.



This video compression standard is compatible to PAL and NTSC and works on the video standard YCrCb. It samples the Y component to 352 * 288 pixels according to the Common Intermediate Format (CIF) or 176 * 144 pixels according to the Quarter Common Intermediate Format (QCIF). The frame rate is 29.97 frames/s. H.261 makes use of interframe redundancy. It just codes the difference of the predecessor frame and just sends in a certain interval a full frame.



Video compression for low bit-rate communication. This is the enhancement of the H.261 standard. The algorithms of H.261 had been fine tuned and enhanced so that the compression increases by a factor 2 at the same quality. It works on 64 kbit/s bandwidth.



MPEG-1 was developed for digital video recording and playback. The standard works on a quiet similar way like H.261. Except of the advantage searching forward and backward in the frames. It is also a differential compression used. Each frame has its unique sequence number and timestamp. This gives the ability of receiving the frames in a different sequence that there are shown. It is designed for a bandwidth of 1.5 Mbit/s and contains the audio standard MUSICAM. The quality is comparable to VCR video quality.



MPEG-2 is the successor standard of MPEG-1. It covers digital TV (HDTV) standards and is based on a 4 - 10 Mbit/s bandwidth. A major change to MPEG-1 is the ability of working on interlaced frames. The sound supports quadro and surround options.