Apple Compressor 3 User Manual download pdf (Page 90)

Importing MPEG-2 Files

When you import an MPEG-2 file, Compressor must parse the file before you can play it

in the Preview window. Parsing the file involves determining its frame structure and other

necessary information about the file. Since the frame structure can change throughout

the file, Compressor must scan through the entire file, which can take several minutes

for longer files.

This does not happen with MPEG-2 elementary files encoded using Compressor that had

the “Add DVD Studio Pro metadata” checkbox selected. See Extras Tab for more

information.

About Dolby Digital Professional Source Media Files

You can use Dolby Digital Professional AC-3 audio files as source media files for your jobs.

There are two common reasons to want to do this.

• To test a file you just encoded: Since you cannot preview the Dolby Digital Professional

output settings, importing an encoded file into a job allows you to play it and verify

the settings.

• To convert a Dolby Digital audio file to another format: Since not all media players include

Dolby Digital decoders, you may find that you need to transcode the file into another

format.

Compressor includes a Dolby Digital decoder that it uses whenever you play or transcode

Dolby Digital audio files. This makes it possible to verify the Dolby Digital Professional

output settings of a previously encoded file on your system without requiring you to

have an external Dolby Digital decoder. To hear surround sound you must have an external

surround sound device connected to your computer’s USB or FireWire output. The audio

is mixed down to two channels if you play the audio using your system’s stereo speakers.

Important: Since the audio output is already decoded and not in the Dolby Digital format,

the optical output cannot be used when playing Dolby Digital files from Compressor.

Tip: Add an .ac3 extension to the filename if Compressor does not allow you to add it to

a job.

Automatic Values and Nonstandard QuickTime Files

Compressor uses a variety of tactics to determine the proper values for any settings that

are set to Automatic. In most cases, QuickTime files contain metadata that specify the

various attributes of the file, such as frame rate and frame size. In some cases, this metadata

is not present, forcing Compressor to try to determine this information, or it is incorrect,

causing Compressor to generate incorrect values for the Automatic settings.

Additionally, some QuickTime files use nonstandard settings that require Compressor to

choose an automatic value that may not be suitable.

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Apple Compressor 3 User Manual Page 90