4.5

Table Of Contents
181Compressor User Guide
Glossary
AAC (Advanced Audio Coding) Also called MPEG-4 Audio. A standard way of compressing
and encoding digital audio. AAC-encoded files rival the quality of audio CDs and generally
sound as good as or better than MP3 files encoded at the same or even a higher bit rate.
AC-3 (Audio Codec 3, Advanced Codec 3, Acoustic Coder 3) A Dolby Digital compressed
audio format often used for encoding surround sound.
AIFF (Audio Interchange File Format) A cross-platform audio file format developed by
Apple. Like WAV files, AIFF files contain “chunks” of information such as the Sound Data
Chunk, which contains the actual sample data, and the Common Chunk, which contains
sample rate and bit depth information.
ALAC (Apple Lossless Audio Codec) A lossless audio codec developed by Apple. ALAC
supports up to eight channels of audio, with a maximum sample depth of 32 bits and a
maximum sample rate of 384 kHz.
alternative audio Translated dialog tracks, commentary, or audio descriptions (for the
visually impaired) included in an iTunes Store package.
Apple ProRes Apple ProRes codecs provide an unparalleled combination of multistream,
real-time editing performance, impressive image quality, and reduced storage rates.
Apple ProRes codecs take full advantage of multicore processing and feature fast,
reduced-resolution decoding modes. All Apple ProRes codecs support any frame size
(including SD, HD, 2K, and 4K) at full resolution. The data rates vary based on codec type,
image content, frame size, and frame rate.
Apple ProRes includes the following formats:
Apple ProRes 4444 XQ: The highest-quality version of Apple ProRes for 4:4:4:4 image
sources (including alpha channels), with a very high data rate to preserve the detail
in high-dynamic-range imagery generated by today’s highest-quality digital image
sensors. Apple ProRes 4444 XQ preserves dynamic ranges several times greater than
the dynamic range of Rec 709 imagery—even against the rigors of extreme visual
effects processing, in which tone-scale blacks or highlights are stretched significantly.
Like standard Apple ProRes 4444, this codec supports up to 12 bits per image channel
and up to 16 bits for the alpha channel. Apple ProRes 4444 XQ features a target data
rate of approximately 500 Mbps for 4:4:4 sources at 1920 x 1080 and 29.97 fps.