Apple Compressor 2 Manual de usuario descargar pdf (Pagina 175)

Chapter 12 Creating QuickTime Movie Output Files 175

Compressor comes equipped with the standard video codecs that QuickTime offers

and the additional codec options that come with QuickTime Pro. Unless you know your

target audience has a particular codec installed on their computers, you should use

one of the standard QuickTime codecs to ensure universal conformity.

Note: See the relevant QuickTime documentation for more information about choosing

video codecs and how to get the best out of the video codec settings.

Video codecs can be divided into the following two types:

Â Lossless codecs: Lossless codecs completely preserve the data they compress, and are

usually used to transfer footage from one editing suite to another. Lossless codecs can

require high data rates and high-end computers with specialized hardware. Examples

of lossless codecs are the Animation, 8-bit, and 10-bit uncompressed 4:2:2 codecs.

Â Lossy codecs: In comparison to lossless codecs, lossy codecs only return an

approximation of the data and are usually used to deliver finalized video to an end

user. The level of approximation is determined by the quality of the codec. Typically

there is a tradeoff between the output quality of the codec and its achievable level of

compression. With some codecs, a compression ratio of at least 5:1 can be reached

without visible degradation. An example of a lossy codec is the Photo-JPEG codec.

Low-quality lossy compression introduces unnatural visual artifacts which may

become noticeable to the human eye. Using a lossy codec, you should only compress

your media file once, because compressing a file multiple times adds more artifacts.

QuickTime Audio Codecs

If you have the disk space and bandwidth, the best thing you can do is leave your

audio uncompressed. Uncompressed audio normally uses 8-bit (phone quality) or

16-bit (CD quality) samples. (Compressor 2 supports up to 64 bits per sample floating

point and a maximum sample rate of 192 kHz.) If you have disk space and bandwidth

limitations, you must compress your audio. However, audio takes up less disk space

than video, so it doesn’t need to be compressed as much as video.

The two most important components of audio codecs are sampling rates and size.

Sampling rate sets the sound quality, and sampling size sets the dynamic range of the

sound. QuickTime audio codecs allow you to set both the sampling rate and size of

your source media file.

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Apple Compressor 2 Manual de usuario Pagina 175