Mp3 files, Mp3 overview, Mp3 transcoding workflow – Apple Compressor (4.0) User Manual
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Chapter 5
Custom settings and output formats
104
MP3 files
MP3 overview
MP3 is a specific type of MPEG encoding known formally as MPEG Audio Layer 3. MP3 uses
perceptual audio coding and psychoacoustic compression to remove all superfluous information
(specifically the redundant and irrelevant parts of a sound signal that the human ear doesn’t hear
anyway). The result is that MP3 encoding shrinks the original sound data from a CD (with a data
rate of 1411.2 kilobits per second of stereo music) by a factor of 12 (down to 112 to 128 kbps) without
sacrificing very much sound quality. Proponents of MP3 actually claim that there is no sacrifice in
sound quality, but audio professionals can usually hear the difference on good equipment.
MP3 is a widely adopted standard for compressed audio files, so it can be used in many different
ways, including for music and podcasts.
Music
Almost every portable digital music player supports the MP3 audio format. By using the higher
bit rates, for example 256 kbps, you can create an excellent-quality audio file using a much
smaller file size than with uncompressed audio.
You can also add metadata to the file so that when the output media file opens in many players
(including iTunes), information such as the artist and the album name appears.
Podcasts
The MP3 format’s wide range of supported bit rates makes it ideal for delivering podcasts at a
variety of quality levels, making it possible for people listening to the podcast to choose a file
size and quality level.
Note: For the most options when creating enhanced audio podcasts, use the MPEG-4 output
format. You can add chapter and podcast markers with URLs and artwork to the output file. For
more information, see
on page 114.
MP3 transcoding workflow
How you use Compressor to transcode your audio into MP3 format files depends on how you
intend them to be used. The basic workflow is described below.
Stage 1: Create a batch
As with any transcode, you need to start by creating a batch. For more information, see
on page 18.
Stage 2: Create jobs with the source audio files
Import the source audio files either by dragging them from the Finder to the batch or by
choosing Job > New Job With File.
Stage 3: Add annotations (if needed)
If you intend to play the MP3 files with a device or an application such as iTunes, you can add a
variety of annotations, such as artist, album, title, and so on, that can be read and displayed. For
more information, see
on page 27.