4.5

185Compressor User Guide
HLG (hybrid log-gamma) A mathematical HDR transfer function that converts image
signal values in a video file to scene-relative light levels. HLG, which was developed by
the BBC and the NHK (Japan Broadcasting Corporation), requires no metadata and is also
compatible with SDR displays. In Compressor, HLG is used with the Rec. 2020 color space
to create video files in the hybrid log-gamma HDR standard.
i-frame (intra-coded picture) One type of frame used to define the GOP (Group of
Pictures) pattern used during MPEG-2 or H.264 encoding. A GOP pattern can also include
P-frames (predictive coded picture) and B-frames (bipredicitive coded picture)
interlaced video Video to be played on traditional NTSC or PAL televisions is stored using
an interlaced frame rate. Each frame is actually made up of two half-frames called fields.
Each field contains half the frame lines; the odd (or upper) field contains lines 1, 3, 5, 7, 9
and so on, and the even (or lower) field contains lines 2, 4, 6, 8, 10, and so on. When the
video is played back, the TV displays the fields in an alternating pattern, which creates an
effective illusion of smooth movement. Viewing interlaced video on a computer screen that
displays both fields simultaneously may reveal a combing effect. Progressive video frame
rates store the video in a series of whole frames instead these two-fields. You can remove
the fields from an interlaced video clip by converting it to a progressive frame rate.
iTT (iTunes Timed Text) subtitles An industry-standard format for delivering onscreen
text synchronized to the audio or video of a video program. iTT subtitles can be used
to deliver foreign-language translations or a transcript of dialog, narration, or audio
descriptions to people who are deaf or hard of hearing. iTT subtitles, which use the .itt
filename extension, offer more limited formatting options than CEA-608 captions. In
Compressor, you can specify whether to let viewers turn iTT subtitles on or off (for
example, for full foreign-language translations) or force subtitles to appear onscreen (for
example, for specific characters in a movie who speak a different language). In Compressor,
iTT subtitles are compatible with iTunes Store packages and many transcode settings.
iTunes Store package Publishers who submit videos to the iTunes Store must deliver their
content in a carefully prescribed format called an iTunes Store package. Compressor can
create these packages, provided you have all the requisite components (video files, audio
files, subtitle files, closed-caption files, and so on).
job In Compressor, the source media file and output instructions (one or more output rows,
each containing a setting, location, and file name), ready to be transcoded.
job action In Compressor, an action that is performed on a media file after it is transcoded.
For example, a job action can add a transcoded file to your Home Videos library on
Apple TV or run an Automator workflow.
keyframe interval A keyframe is a frame that stores a complete image. Keyframes provide
the entire image in the video stream; after that image is provided, incremental changes
between related frames are stored (not the entire image). Thus, when the image in the
video changes dramatically, for example, when switching between images, a keyframe must
be created to mark the location of change. It’s recommended that you allow Compressor
to determine the key frame interval for your output file; however, you can also set the key
frame interval manually.
location In Compressor, the location where your transcoded media file is saved. You can
either use the default location (the same folder the source media file is in) or choose a
custom location.