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.

• Apple ProRes 4444: An extremely high-quality version of Apple ProRes for 4:4:4:4 image sources (including alpha channels). This codec features full-resolution, mastering-quality 4:4:4:4 RGBA color and visual fidelity that is perceptually indistinguishable from the original material. Apple ProRes 4444 is a high-quality solution for storing and exchanging motion graphics and composites, with excellent multigeneration performance and a mathematically lossless alpha channel up to 16 bits. This codec features a remarkably low data rate compared to uncompressed 4:4:4 HD, with a target data rate of approximately 330 Mbps for 4:4:4 sources at 1920 x 1080 and 29.97 fps. It also offers direct encoding of, and decoding to, both RGB and Y’C_BC_R pixel formats.

• Apple ProRes 422 HQ: A higher-data-rate version of Apple ProRes 422 that preserves visual quality at the same high level as Apple ProRes 4444, but for 4:2:2 image sources. With widespread adoption across the video post-production industry, Apple ProRes 422 HQ offers visually lossless preservation of the highest-quality professional HD video that a single-link HD-SDI signal can carry. This codec supports full-width, 4:2:2 video sources at 10-bit pixel depths, while remaining visually lossless through many generations of decoding and reencoding. The target data rate of Apple ProRes 422 HQ is approximately 220 Mbps at 1920 x 1080 and 29.97 fps.

• Apple ProRes 422: A high-quality compressed codec offering nearly all the benefits of Apple ProRes 422 HQ, but at 66 percent of the data rate for even better multistream, real-time editing performance. The target data rate of Apple ProRes 422 is approximately 147 Mbps at 1920 x 1080 and 29.97 fps.

• Apple ProRes 422 LT: A more highly compressed codec than Apple ProRes 422, with roughly 70 percent of the data rate and 30 percent smaller file sizes. This codec is perfect for environments where storage capacity and data rate are at a premium. The target data rate of Apple ProRes 422 LT is approximately 102 Mbps at 1920 x 1080 and 29.97 fps.

• Apple ProRes 422 Proxy: An even more highly compressed codec than Apple ProRes 422 LT, intended for use in offline workflows that require low data rates but full-resolution video. The target data rate of Apple ProRes 422 Proxy is approximately 45 Mbps at 1920 x 1080 and 29.97 fps.

• Apple ProRes RAW: The Apple ProRes RAW and Apple ProRes RAW HQ codecs preserve all of the camera sensor’s pristine raw data to deliver extraordinarily high-quality images. ProRes RAW brings to raw video the same great performance, quality, and ease of use that ProRes has brought to conventional video, in a format ideal for HDR content creation. Being able to use the raw image sensor data directly in Final Cut Pro during post-production gives you more control over the processing of the image, including demosaicing, linear-to-log conversions, and custom LUTs.

Note: Apple ProRes 4444 and Apple ProRes 4444 XQ are ideal for the exchange of motion graphics media because they are virtually lossless, and are the only Apple ProRes codecs that support alpha channels.

AVCHD

A high-definition (HD) video format that uses Advanced Video Coding (AVC) compression (also known as MPEG-4 part 10 or H.264). Many Blu-ray players can play red laser discs with AVCHD format content, making this a common way to distribute short HD video projects using a standard red laser disc.

batch

In Compressor, one or more jobs to be processed. All jobs contained within the batch (shown in the batch area of the Compressor window) are submitted collectively when you begin the transcoding process. There are two types of batches in Compressor: standard batches, used for most transcoding jobs, and iTunes Store packages, a special workflow for submitting content to the iTunes Store.

bit rate

The number of bits per second in the transmission of a digital video or audio signal. The higher you set the bit rate, the better the quality of the output file. However, higher bit rates require larger file sizes.

CAF (Core Audio Format)

Apple’s Core Audio Format is a flexible file format for storing and manipulating digital audio data. CAF provides high performance and flexibility, and is scalable to future ultra high-resolution audio recording, editing, and playback.

captions

In Compressor, onscreen text synchronized to the audio or video of a video program. Compressor supports three industry-standard caption formats: CEA-608 closed captions, iTT (iTunes Timed Text) subtitles, and SRT (SubRip Text) subtitles.

CEA-608 closed captions

An industry-standard format for delivering onscreen text synchronized to the audio or video of a video program. Originally developed for people who are deaf or hard of hearing, CEA-608 closed captions (also known as Line 21 text) are frequently used on televisions in loud environments (such as bars and airports). CEA-608 closed captions, which use the .scc filename extension, offer numerous formatting options. Viewers can turn closed captions on or off while watching television shows, movies, web videos, and other programs. In Compressor, CEA-608 closed captions are compatible with iTunes Store packages and many transcode presets.

codec

Short for COmpression/DECompression. A software component used to translate video or audio from its current form to a different, digitally compressed form. A codec encodes a data stream or signal for transmission, storage or encryption, or decodes it for playback or editing. A similar term, encoder, is used to describe hardware that performs the same activity.

color space

The range of colors available for an image, sometimes called gamut. A wider gamut allows for more possible color values and permits more accurate representation of color.

delivery partner

A content aggregator or encoding house certified by the iTunes Store and authorized to submit iTunes Store packages to the store for sale. These partners ensure your content is properly configured and formatted to meet the stringent submission requirements of the iTunes Store. They can also provide billing and support services after your video becomes available for sale.

descriptive audio

An alternative audio track in an iTunes Store package that includes voice narration to help visually impaired consumers understand what’s happening onscreen. Descriptive audio narration is usually delivered during the natural pauses in dialog or between critical sound elements. An iTunes Store package can contain multiple descriptive audio tracks (in multiple languages, for example).

destination

In Compressor, a group of one or more transcode presets plus a post-transcoding action. If you use a destination to transcode a file, one or more new files are created to the preset’s specifications and then an action is automatically performed on the transcoded file. For example, the Add to TV Home Videos destination creates a file optimized for viewing on Apple TV. After the file is processed, the Add to TV Home Videos action automatically copies the output file to your Home Videos library on Apple TV.

display aspect ratio

The ratio between an image’s width and height. For example, standard-definition (SD) video typically has an aspect ratio of 4:3. High-definition (HD) video typically has an aspect ratio of 16:9. If SD video is played on an HD display, the image is either stretched, or is appended with black borders on left and right sides (pillarboxing). If HD video is played on an SD display, the image will be squeezed or black borders will appear at the top and bottom (letterboxing).

distributed processing

A method of transcoding that accelerates processing of Compressor batches by distributing the work among multiple computer processors. A system can distribute parts of a batch to multiple instances of the Compressor application on a single computer, or to two or more networked computers (each running one or more instances of Compressor).

droplet

A lightweight, standalone app created by Compressor to apply specific presets or destinations to media files. You can drag and drop media files onto the droplet icon in the Finder to begin transcoding.

Dolby Digital

See AC-3.

Dolby Digital Enhanced

See E-AC-3.

E-AC-3

A Dolby Digital compressed audio format often used for encoding surround sound. E-AC-3 supports up to fifteen channels of audio.

encoder

See codec.

file format

The output format used to transcode your source media file. Also called a transcoding format.

FLAC (Free Lossless Audio Codec)

A lossless audio format that supports up to 8 channels of audio and up to 32 bit sample depth.

H.264

A video compression standard in widespread use for recording, distribution, and Internet streaming of high-definition (HD) video. Also known as MPEG-4 Part 10 or AVC (Advanced Video Coding).

HDR (high dynamic range)

Video stored in a format that processes higher levels of luminance (brightness) per color component to provide significant improvements in contrast, detail, and light levels over standard-dynamic-range (SDR) video. HDR can represent luminances as high as 10,000 nits (candelas per square meter) with a dynamic range of 14 stops or more, creating more realistic color transitions and revealing more detail in both shadows and highlights. HDR video is typically combined with wide-gamut color spaces such as Rec. 2020 or P3 D65 to deliver video any of several formats, including HDR10, Dolby Vision, and HLG (hybrid log-gamma).

HEVC

High-Efficiency Video Coding (also known as H.265), a recently established compression standard designed to reduce file size while retaining a high-quality image. HEVC also supports larger frame sizes (including 8K) and HDR10 metadata for high-dynamic-range video. The Apple Devices transcode preset in Compressor includes two built-in options for HEVC output. You can also customize the MPEG-4 and QuickTime Movie presets to use the HEVC encoder. HEVC encoding in Compressor requires macOS 10.13 or later. HEVC playback requires an Apple device running macOS 10.13, iOS 11, iPadOS 13, tvOS 11, or later.

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 presets.

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 preset, location, and file name), ready to be transcoded.

job action

In Compressor, an action that is performed on a media file after it’s 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 keyframe interval for your output file; however, you can also set the keyframe 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.

lower third

A television industry term for a graphic placed in the lower area of the screen, usually to convey details about subjects or products. A common use of lower thirds is to identify individuals on the screen with their names and job titles.

marker

A marker flags a specific timing location in a source file. You can append a marker with editing notes or other descriptive information. Additionally, when you output the source file to an H.264, MPEG-2, or MPEG-4 video format, each marker forces the creation of an I-frame. Added I-frames improve compression quality, but can increase overall file size. Compressor can create the following types of markers:

• Chapter markers: Generate named index points and thumbnail images for DVDs, QuickTime movies, or video podcasts. You can also assign a URL to a chapter marker to have that URL appear during playback of a podcast. Chapter markers are also included in submissions to the iTunes Store as part of an iTunes Store package. Chapter markers appear orange in the Compressor preview area.

• Compression markers: Generate an I-frame, but do not generate thumbnails, chapter-track entries, or other metadata. Add them to a video if a section appears to have lower image quality than the surrounding frames. Compression markers appear blue in the Compressor preview area.

• Edit markers: Function identically to compression markers. They are commonly used by compression artists to force an I-frame at an edit point to ensure higher image quality at that moment in the video. Edit markers appear red in the Compressor preview area.

• Podcast markers: Like chapter markers, podcast markers can have artwork and a URL assigned to them. Podcast markers are usually used to provide a slideshow (with URLs) for users to view when playing audio podcasts. However, podcast marker names do not appear in the slideshow, and users cannot navigate to a podcast marker in the transcoded file. Podcast markers appear purple in the Compressor preview area.

matrix stereo

A stereo downmix of a surround track for playback on a device with only two speakers; matrix stereo can also be decoded to play the full surround mix on a surround-capable playback device.

MP3

Refers to the MPEG-1 or MPEG-2 Audio Layer 3 compression standard and file format. Like AAC, MP3 uses perceptual audio coding and psychoacoustic compression to remove superfluous information that the human ear doesn’t hear.

nit

A unit of measure describing the luminance (light intensity) of a video display. One nit’s equal to one candela per square meter.

output row

In Compressor, an output row in a job contains the instructions used for transcoding a source media file. An output row includes a preset (shown on the left) that specifies properties defining how to transcode the source media file, a location (shown in the middle) where the transcoded file will be saved, and a filename (shown on the right) for the transcoded file.

P3 D65

Also known as Display P3, a wide-gamut color space based on the DCI-P3 color standard developed for digital movie projection. P3 D65 is the display color space of recent Apple devices, including the iMac (with Retina 4K or 5K display), MacBook Pro, and iPad Pro.

PQ (perceptual quantizer)

A mathematical transfer function that converts image signal values in a video file to absolute light levels on an HDR-capable display. Designed to approximate the sensitivity of human eyes, PQ allows for better levels of contrast at all light levels. In Compressor, PQ is used with the Rec. 2020 and P3 D65 wide-gamut color spaces to create video files in the industry-standard HDR formats, HDR10 and Dolby Vision.

preview area

In Compressor, the area where you can play your source file and preview your output file. After you apply effects or change the properties of the preset that will transcode your source file, you can compare the “before” and “after” versions by clicking the Comparison button (under the timeline). The screen is divided by a vertical white line, with the source file shown on the left and the preview of the transcoded file shown on the right.

QuickTime

The cross-platform multimedia technology that allows macOS and Windows applications to capture and play back video, audio, and still-image files.

Rec. 709

The standard-gamut 8-bit color space used by high-definition TV displays, the Blu-ray Disc format, and most TV broadcasters. Also known as ITU-R Recommendation BT.709.

Rec. 2020

A wide-gamut color space developed for future consumer display devices but useful today for mastering (to future-proof your projects) and for 4K and 8K TV projects. Even though no currently available consumer TVs or computer monitors can display the entire Rec. 2020 palette, wide-color-gamut displays can show a subset of those colors. Also known as ITU-R Recommendation BT.2020.

resolution

Image resolution refers to the frame size of the video. Image resolution is expressed in terms of the width and height (the frame size) of the image in pixels. Higher-resolution images contain more detail but also create larger files that take longer to download. Your electronic devices (computer, iPhone, iPad, iPod, and so on) also have screen resolution. Resolution is expressed in terms of the width and height of the image in pixels (for example, 640 x 360 pixels).

When you add a preset to a source media file, Compressor determines appropriate resolution sizes you can use, based on the image sizes used in the movie and on the preset that you’re using to output the file.

sample rate

The number of times per second that music waveforms (samples) are captured digitally. The higher the sample rate, the higher the quality and the larger the file size.

sample size

The number of bits in each audio sample; determines the potential dynamic range of the sound.

SDR (standard dynamic range)

The conventional technique for processing luminance (levels of brightness) and color values in images, developed in the mid-1900s, with an upper luminance limit of 100 nits (candelas per square meter) and a dynamic range of 6–10 stops.

preset

In Compressor, a group of preconfigured properties that you can apply to a source media file. Presets are used to transcode files into commonly used audio and video formats for Apple devices, podcasting, Internet streaming, post-production, and so on. Each preset includes adjustable properties like output file format, retiming instructions, and optional effects.

source media file

In Compressor, the original media file to be converted to a new file format. One source file is required for each job.

SRT (SubRip Text subtitles)

An industry-standard format for delivering onscreen text synchronized to the audio or video of a video program. SRT 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. SRT subtitles, which use the .srt filename extension, offer more limited formatting options than CEA-608 captions. In Compressor, you can specify whether to let viewers turn SRT 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, many built-in presets and destinations support SRT subtitles, including Apple Devices (in both the H.264 and HEVC codecs), ProRes, Create DVD, and other presets that use the QuickTime Movie, MPEG-2, and MPEG-4 formats.

storage aspect ratio (SAR)

The ratio between an image’s width and height when it’s stored. Storage aspect ratio can differ from display aspect ratio (DAR) resulting in a file that must be stretched or squeezed during playback to appear correct. This disparity can allow a camera format limited to 4:3 recording to successfully record a widescreen image by “squeezing” the image during recording. If the image is unsqueezed during playback it will display correctly in its widescreen aspect ratio. This is called an anamorphic image.

transcoding

The process of converting files from their original format to a different format. Closely related terms include compression, which specifically refers to data reduction, and encoding, a term that is essentially synonymous with transcoding, but doesn’t emphasize the conversion aspect.

uncompressed 8-bit and 10-bit 4:2:2

Video formats used to store 8-bit or 10-bit 4:2:2 Y’C_BC_R video without employing data compression. Bypassing compression reduces the computer’s processing load but increases the data rate considerably. A large-capacity RAID storage system is typically required to work effectively with uncompressed video. In many cases, Apple ProRes is a better choice.

The data rate of uncompressed 4:2:2 video varies according to frame size and frame rate. For example, at a frame size of 1920 x 1080 and a frame rate of 29.97 fps, the data rate is 1.0 Gbps for uncompressed 8-bit 4:2:2 video and 1.3 Gbps for uncompressed 10-bit 4:2:2 video.

WAVE (or WAV)

An audio file format most commonly used for storing uncompressed linear pulse code modulation (LPCM) audio data.

wide color gamut

A video color space capable of reproducing a broader palette of colors than traditional standard-gamut color spaces. Recent display devices—including 4K televisions and computer monitors, newer Mac, iOS, and iPadOS devices, and Apple TV 4K (when connected to a wide-gamut television)—can render more vivid and lifelike hues (in addition to all the hues that standard-gamut devices can display). Accordingly, the video industry has adopted a wide-gamut color standard called Rec. 2020. Although most currently available wide-gamut devices support only a subset of the colors contained in the full Rec. 2020 specification, future imaging devices should be able to render more and more of those hues.