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QuickTime File Format
View on Wikipediafrom Wikipedia
| QuickTime Movie | |
|---|---|
| Filename extension |
.mov, .movie, .qt |
| Internet media type | |
| Type code | MooV |
| Uniform Type Identifier (UTI) | com.apple.quicktime-movie |
| Developed by | Apple Inc. |
| Initial release | Proprietary: December 2, 1991 Public: March 1, 2001[3] |
| Latest release | September 13, 2016[4] |
| Type of format | Container format |
| Container for | Audio, video, text |
| Extended to | MPEG-4 Part 12 |
| Open format? | Yes |
| Free format? | No[5] |
QuickTime File Format (QTFF) is a computer file format used natively by the QuickTime framework.[6][7][8]
Design
[edit]The format specifies a multimedia container file that contains one or more tracks, each of which stores a particular type of data: audio, video, or text (e.g. for subtitles). Each track either contains a digitally-encoded media stream (using a specific format) or a data reference to the media stream located in another file. Tracks are maintained in a hierarchical data structure consisting of objects called atoms. An atom can be a parent to other atoms or it can contain media or edit data, but it is not supposed to do both.[9]
The ability to contain abstract data references for the media data, and the separation of the media data from the media offsets and the track edit lists means that QuickTime is particularly suited for editing, as it is capable of importing and editing in place (without data copying). Other later-developed media container formats such as Microsoft's Advanced Systems Format or the Matroska and Ogg containers lack this abstraction, and require all media data to be rewritten after editing.
Relation to MP4
[edit]Because both the QuickTime and MP4 container formats can use the same MPEG-4 formats, they are mostly interchangeable in a QuickTime-only environment. MP4, being an international standard, has more support. This is especially true on hardware devices, such as the PlayStation Portable and various DVD players; on the software side, most DirectShow and Video for Windows codec packs[10][11] include an MP4 parser, but not one for QTFF.
In QuickTime Pro's MPEG-4 Export dialog, an option called "Passthrough" allows a clean export to MP4 without affecting the audio or video streams. One discrepancy ushered in by QuickTime 7 released on April 29, 2005, is that the QuickTime file format supports multichannel audio (used, for example, in the high-definition trailers on Apple's site[12]).
Extensions
[edit]The International Organization for Standardization approved the QuickTime file format as the basis of the MPEG-4 file format. The MPEG-4 file format specification was created on the basis of the QuickTime format specification published in 2001.[13] The MP4 (.mp4) file format was published in 2001 as the revision of the MPEG-4 Part 1: Systems specification published in 1999 (ISO/IEC 14496-1:2001).[14][15][16] In 2003, the first version of MP4 format was revised and replaced by MPEG-4 Part 14: MP4 file format (ISO/IEC 14496-14:2003).[17] The MP4 file format was generalized into the ISO Base Media File Format ISO/IEC 14496-12:2004, which defines a general structure for time-based media files. It in turn is used as the basis for other multimedia file formats (for example 3GP, Motion JPEG 2000).[18][19][20][21][22] A list of all registered extensions for ISO Base Media File Format is published on the official registration authority website www.mp4ra.org. This registration authority for code-points in "MP4 Family" files is Apple Inc. and it is named in Annex D (informative) in MPEG-4 Part 12.[21]
See also
[edit]References
[edit]- ^ "Video Media Types". IANA. June 4, 1993. Retrieved July 20, 2010.
- ^ Gellens, R.; Singer, D.; Frojdh, P. (November 2005). "The Codecs Parameter for "Bucket" Media Types". IETF. doi:10.17487/RFC4281. Retrieved July 20, 2010.
- ^ "QuickTime File Format" (PDF). Apple Developer. Apple. March 1, 2001. Archived (PDF) from the original on October 6, 2021. Retrieved December 13, 2021.
- ^ "QuickTime File Format Specification - Document Revision History". Apple Developer. September 13, 2016. Retrieved December 13, 2021.
- ^ QuickTime File Format (Full draft). Sustainability of Digital Formats. Washington, D.C.: Library of Congress. February 14, 2013. Retrieved December 13, 2019.
- ^ Apple Inc. "QuickTime File Format Specification: Introduction to QuickTime File Format Specification". Retrieved October 9, 2018.
- ^ AfterDawn.com. "QuickTime - AfterDawn.com glossary". Retrieved July 20, 2010.
- ^ "QuickTime container". MultimediaWiki. Retrieved July 20, 2010.
- ^ Apple Inc. "QuickTime File Format Specification: Movie Atoms". Retrieved October 9, 2018.
- ^ DefilerPak – A lightweight codec pack for Windows PCs Archived August 15, 2015, at the Wayback Machine
- ^ K-LiteCodecPack.com: Download Codecs, Videos and MP3s
- ^ "iTunes Movie Trailers". trailers.apple.com. Archived from the original on February 13, 2010.
- ^ Apple Inc. (2001). "Classic Version of the QuickTime File Format Specification". Retrieved June 14, 2009.
- ^ Library of Congress (2001). "MPEG-4 File Format, Version 1". Retrieved June 14, 2009.
- ^ Network Working Group (2006). "RFC 4337 – MIME Type Registration for MPEG-4". doi:10.17487/RFC4337. Retrieved June 14, 2009.
- ^ International Organization for Standardization (2001). "MPEG-4 Part 1: Systems; ISO/IEC 14496-1:2001". Retrieved June 11, 2009.
- ^ International Organization for Standardization (2003). "MPEG-4 Part 14: MP4 file format; ISO/IEC 14496-14:2003". Retrieved June 11, 2009.
- ^ mp4ra.org – MP4 Registration authority. "References, MPEG-4 Registration authority". Archived from the original on September 10, 2012. Retrieved June 14, 2009.
{{cite web}}: CS1 maint: numeric names: authors list (link) - ^ ISO (April 2006). "ISO Base Media File Format white paper – Proposal". Archived from the original on July 14, 2008. Retrieved December 26, 2009.
- ^ ISO (October 2009). "ISO Base Media File Format white paper – Proposal". chiariglione.org. Retrieved December 26, 2009.
- ^ a b ISO (2008). "ISO/IEC 14496-12:2008, Information technology – Coding of audio-visual objects – Part 12: ISO base media file format" (PDF). International Organization for Standardization. pp. 88, 94. Retrieved May 30, 2009.
- ^ International Organization for Standardization (2004). "MPEG-4 Part 12: ISO base media file format; ISO/IEC 14496-12:2004". Retrieved June 11, 2009.
QuickTime File Format
View on Grokipediafrom Grokipedia
The QuickTime File Format is a flexible, object-oriented multimedia container developed by Apple Inc. for storing, exchanging, and streaming digital video, audio, text, and other media types across platforms and devices.[1][2] Introduced in 1991 as part of Apple's QuickTime multimedia framework, it employs a hierarchical structure of atoms—fundamental data units identified by size and four-character type codes—to separate metadata from actual media samples, enabling efficient parsing, extensibility, and forward compatibility for unknown elements.[3][2]
Key components include the movie atom ('moov'), which encapsulates timing, track definitions, and sample tables for synchronization; track atoms ('trak'), representing individual media streams like video or audio; and the media data atom ('mdat'), holding compressed samples from supported codecs such as Apple ProRes, MPEG-4, or AAC.[3][4] This design supports advanced features like hint tracks for RTP-based streaming, modifier tracks for dynamic edits, sprite animations, and QuickTime VR for panoramic or object-based interactivity, while allowing references to external data sources via URLs or files.[3] The format's adoption extended to Windows in 1994 and influenced the MPEG-4 standard in the late 1990s, with file extensions typically including .mov for movies and .qt for general use, alongside MIME types like video/quicktime.[2] Its full documentation ensures long-term sustainability, though proprietary elements like DRM can complicate preservation.[3][2]
The user data atom ('udta') resides within the 'moov' container and allows storage of arbitrary metadata associated with the movie, including standard entries like title, author, and copyright notices, as well as custom information defined by applications.[3] It functions as a flexible container holding multiple sub-atoms, each with its own size, type, and payload, enabling extensible metadata without altering the core file structure.[3]
For thumbnail and preview functionality, the preview atom ('pnot') within the 'moov' or 'udta' provides details to locate or generate a representative image, such as a modification date (32-bit timestamp), atom type (e.g., 'PICT' for picture data), and atom index (typically 1 for the primary preview).[3] Poster information, often linked via the 'mvhd' postertime field, can integrate with 'udta' variants to specify static frames for quick visual representation during browsing or embedding.[3]
Free space atoms ('free') and skip atoms ('skip') mark unused or padding areas within the movie container, with both consisting solely of size and type fields and no additional data payload.[3] The 'free' atom designates space available for future use or editing, while the 'skip' atom indicates regions that parsers should ignore entirely, enhancing file efficiency and forward compatibility by allowing safe navigation around obsolete or reserved blocks.[3]
Audio codecs emphasize perceptual and lossless compression, with AAC ('mp4a') serving as the primary format for MPEG-4 compatible audio, offering high efficiency at bitrates from 64 to 320 kbps.[21] Uncompressed PCM uses 'sowt' for little-endian 16-bit samples, ensuring fidelity in professional audio tracks.[3] MP3 audio uses 'mp3 ' for direct integration, while Apple Lossless ('alac') provides bit-for-bit reproduction of original WAV or AIFF files without data loss.[21]
Beyond media, QuickTime supports non-video/audio track types for enhanced functionality, including video ('vide') for visual content, audio ('soun') for sound data, text or subtitles ('text' or 'sbtl') for captions and metadata, MIDI ('midi') for musical instrument digital interface sequences, and timecode ('tmcd') for synchronization references.[3][2] These are specified in handler reference atoms to define track roles.[3]
The sample description atom ('stsd') is central to codec integration, containing entries that detail parameters like bit depth, color space (e.g., Y'CbCr for video), sample rate, and channel layout for each track type. For instance, video entries include width, height, and compressor identifiers, while audio entries specify format-specific flags for decoding.[3] This atom ensures interoperability by allowing decoders to interpret media samples correctly, with one or more descriptions per track.
QuickTime's extensibility allows third-party codecs through registered FourCC codes and custom decompressor components, enabling integration of proprietary formats during its active development era.[3] However, following the deprecation of QuickTime 7 in 2016, native support for new third-party codecs has been limited, with emphasis shifting to ISO-derived formats like MP4.[21]
History and Development
Origins and Initial Release
The QuickTime File Format was developed by Apple Inc. starting in 1990 as a core component of the QuickTime multimedia framework, initially targeted at Macintosh systems to enable software-based handling of digital video and audio.[5] A small team led by engineers such as Peter Hoddie and Bruce Leak created the format to address the limitations of early personal computers, which lacked dedicated hardware for multimedia playback, allowing developers to integrate video and sound directly into applications using standard CPU resources.[5] This foundational design emphasized a hierarchical atom structure to organize media data flexibly, supporting timed sequences of audio, video, and other streams within a single file.[3] Apple released the QuickTime File Format proprietarily on December 2, 1991, alongside QuickTime 1.0, marking the first mass-market software solution for playing synchronized color video and audio on personal computers without specialized hardware. The format's initial purpose was to democratize multimedia creation and playback, enabling users and developers to work with digital media on everyday Macintosh machines running System 6, and it quickly became integral to applications like video editing tools.[6] At launch, the format adopted the file extensions .mov and .qt, with the MIME type video/quicktime, to standardize identification and handling of QuickTime movies across systems and networks.[7] This setup facilitated seamless embedding of multimedia content in documents and web pages, laying the groundwork for broader adoption in the early digital video era.[6]Evolution into International Standards
Originally released as a proprietary format in 1991, the QuickTime File Format underwent a significant shift toward openness with the public release of its full specification on March 1, 2001, through Apple's developer documentation, enabling broader adoption and development by third parties.[3] This openness facilitated the format's integration into international standards, serving as the foundational basis for the MP4 container in MPEG-4 Part 14 (ISO/IEC 14496-14:2003), which standardized the structure for multimedia files while retaining core elements like the atom-based hierarchy.[2] The format further evolved into the more general ISO Base Media File Format (ISO/IEC 14496-12:2004), which generalized the QuickTime structure to support a wider range of media types and applications beyond video.[8] Apple assumed the role of registration authority for code-points in the MP4 family under this standard, managing identifiers for atoms, brands, and other elements to ensure consistent implementation across derivatives.[9] Key updates continued to refine the format's capabilities while preserving its foundational design. The release of QuickTime 7 on April 29, 2005, introduced support for multichannel audio, allowing up to 24 channels including configurations like 5.1 and 7.1 surround sound, which enhanced compatibility with advanced audio workflows. The specification received its final major revision on September 13, 2016, incorporating updates such as expanded color space support in the 'colr' atom for standards like DCI P3 and ITU-R BT.2020.[10] Subsequent clarifications in 2024, as documented by the Library of Congress, addressed specifics like the storage of closed caption media tracks using the 'clcp' atom type, ensuring ongoing relevance for archival and accessibility needs.[2] Throughout these transitions, Apple emphasized backward compatibility, designing updates to allow legacy QuickTime files to remain playable and editable in newer versions and ISO-derived formats, thereby minimizing disruption for existing media ecosystems.[1]Core Design Principles
Hierarchical Atom Structure
The QuickTime File Format is built upon atoms as its fundamental data units, enabling a modular and extensible structure for multimedia content. Each atom begins with a 4-byte size field, stored in big-endian byte order, indicating the total length of the atom in bytes, including the size and type fields themselves; a value of 0 signifies that the atom extends to the end of the file, while a value of 1 indicates the use of a 64-bit extended size field. Immediately following is a 4-byte type field, represented as a FourCC (four-character code) identifier, such as 'moov' or 'trak', which uniquely specifies the atom's purpose and data format. The remainder of the atom consists either of data payload for leaf atoms or a sequence of child atoms for container atoms, allowing for variable content organization without fixed offsets.[11][3] Atoms in the QuickTime format are classified into three primary types based on their function within the hierarchy. Container atoms serve as parents, encapsulating other atoms to form nested structures, such as the 'moov' atom that holds track-level information. Leaf atoms contain only data fields or tables, without any child atoms, and are used to store specific metadata like timing or sample descriptions. Data reference atoms, often functioning as specialized containers, point to the location of media data, either within the same file or in external resources, facilitating shared or remote content access. This categorization supports the format's flexibility in handling diverse media elements.[11][3] The atoms form a hierarchical tree structure, with the root-level movie atom ('moov') overseeing the entire file's content organization. Child atoms nest within parents in a parent-child-sibling sequence, enabling arbitrary levels of nesting for complex media descriptions; for instance, the 'moov' atom may contain multiple track atoms ('trak'), each further subdivided into media and sample-related atoms. This tree-like arrangement allows parsers to traverse the structure sequentially, skipping unrecognized atoms by using the size field, which promotes forward compatibility and extensibility. Tracks emerge as higher-level organizers built from these atomic groupings, coordinating media streams across the hierarchy.[11][3] To accommodate files exceeding 4 GB, QuickTime supports 64-bit extensions through 'wide' atoms, where the initial size field is set to 1, followed by an 8-byte extended size value and the atom type, permitting atoms larger than 2^32 bytes. This mechanism avoids recalculating offsets across the file during growth, maintaining efficiency in large-scale media handling.[11][3] A key advantage of this atomic hierarchy is its support for non-destructive editing, as the abstraction of media data locations—often via data reference atoms—permits modifications to metadata, such as edit lists or sample properties, without altering the underlying media samples. This separation enables efficient updates, like inserting cuts or overrides, by simply adjusting container atoms, which is particularly valuable in video editing workflows.[11][3]Tracks and Media Organization
In the QuickTime File Format, media content is structured into tracks, which serve as top-level containers for specific types of data such as video, audio, text, or subtitles, with each track maintaining its own independent timeline and duration defined by a time scale and the cumulative sum of sample durations.[3] These tracks are housed within the movie atom and organize time-ordered samples into chunks for efficient access and playback, allowing a single movie to combine diverse media streams without requiring them to share identical temporal parameters.[3] Tracks support edit lists that enable non-linear media access through mappings of movie time to media time, incorporating offsets, durations, and playback rates to facilitate editing operations like segment repetition or reordering without duplicating or rewriting the underlying data.[3] This mechanism, implemented via edit list tables, also accommodates initial empty periods before media playback begins, enhancing flexibility for applications such as video editing or dynamic content assembly.[3] Media data within tracks can be stored inline directly in movie data atoms or referenced externally using data reference atoms, which support URLs, file aliases, or other locations to handle large files and enable streaming by avoiding the need to embed all content in the primary file.[3] This dual storage approach optimizes file size and performance, particularly for networked delivery where external references allow progressive loading of media.[3] Synchronization across tracks is managed through shared or individual time scales—such as the default 600 units per second for movies—and precise sample durations recorded in time-to-sample tables, ensuring aligned playback of multimedia elements like video and audio despite differing sample rates or frame structures.[3] Key frames, identified via sync sample tables, further aid in maintaining temporal coherence during seeking or rendering.[3] A QuickTime movie can incorporate multiple tracks to layer various media types, with track references establishing relationships between them for coordinated presentation, and including specialized hint tracks that provide packetization instructions for streaming protocols without altering local playback behavior.[3] This multi-track capability underpins complex compositions, such as synchronized audiovisual content or interactive elements, while hint tracks specifically facilitate efficient transmission over networks by referencing or selectively copying sample data.[3]File Components and Atoms
Movie-Level Atoms
The movie atom, identified by the four-character code 'moov', serves as the mandatory root container for all metadata describing a QuickTime movie, encapsulating sub-atoms that define the file's overall structure and properties without including actual media samples.[3] This atom is essential for organizing the movie's tracks and timing information, and it is typically positioned at the beginning of the file to enable streaming and progressive playback compatibility.[3] The movie header atom ('mvhd') is a key sub-atom within the 'moov' container, providing global characteristics of the entire movie such as timing parameters and playback settings.[3] It begins with a version field (0 or 1) and flags, followed by fields for creation time and modification time, which represent timestamps in seconds since January 1, 1904 (UTC), using 32-bit integers for version 0 or 64-bit for version 1 to accommodate longer durations.[3] The time scale field specifies the number of time units per second (a 32-bit unsigned integer), while the duration field indicates the total movie length in those units, again with 32-bit or 64-bit sizing based on version.[3] Additional fields include preferred rate (a fixed-point value in 16.16 format, defaulting to 1.0 for normal playback speed), preferred volume (8.8 fixed-point, defaulting to 1.0 for full volume), and a 36-byte matrix structure defining spatial transformations like scaling or rotation for display.[3] Other elements cover preview time and duration (for initial playback segments), poster time (for a representative frame), selection time and duration (default user selections), current time (playback position), and next track ID (for assigning unique identifiers to tracks).[3] To illustrate the 'mvhd' structure, the following table summarizes its primary fields:| Field | Type | Size (bytes) | Description |
|---|---|---|---|
| Version | Unsigned Integer | 1 | Atom version (0 or 1). |
| Flags | Unsigned Integer | 3 | Reserved flags (typically 0). |
| Creation Time | Unsigned Integer | 4 (v0) / 8 (v1) | Movie creation timestamp (seconds since 1904 UTC). |
| Modification Time | Unsigned Integer | 4 (v0) / 8 (v1) | Last modification timestamp. |
| Time Scale | Unsigned Integer | 4 | Time units per second. |
| Duration | Unsigned Integer | 4 (v0) / 8 (v1) | Total duration in time scale units. |
| Preferred Rate | Fixed-Point | 4 | Playback rate (16.16 format). |
| Preferred Volume | Fixed-Point | 2 | Audio volume level (8.8 format). |
| Reserved | Bytes | 10 | Must be zero. |
| Matrix | Bytes | 36 | 3x3 transformation matrix. |
| Preview Time | Unsigned Integer | 4 (v0) / 8 (v1) | Start time for preview. |
| Preview Duration | Unsigned Integer | 4 (v0) / 8 (v1) | Length of preview segment. |
| Poster Time | Unsigned Integer | 4 (v0) / 8 (v1) | Time of poster frame. |
| Selection Time | Unsigned Integer | 4 (v0) / 8 (v1) | Default selection start. |
| Selection Duration | Unsigned Integer | 4 (v0) / 8 (v1) | Default selection length. |
| Current Time | Unsigned Integer | 4 (v0) / 8 (v1) | Current playback time. |
| Next Track ID | Unsigned Integer | 4 | ID for next track. |
Track-Level Atoms and Sample Tables
In the QuickTime File Format, tracks organize media data such as video, audio, or text into independent streams that can be synchronized during playback. Each track is encapsulated within a container atom of type 'trak', which holds essential metadata and sample information specific to that track.[12] The track header atom, denoted by 'tkhd', resides directly within the 'trak' container and defines the core properties of the track, including its temporal and spatial characteristics. It includes fields such as a unique track ID (a 32-bit integer greater than zero to identify the track uniquely), layer (a 16-bit integer for rendering order, where lower values are rendered first), alternate group (a 16-bit integer to group mutually exclusive tracks, such as multiple language audio options), volume (an 8.8 fixed-point value for audio tracks, typically 1.0 for full volume), a 3x3 transformation matrix (nine 32-bit fixed-point values for scaling, rotation, and translation), and track width and height (32-bit fixed-point values in pixels for visual tracks). The duration field, expressed in the movie's timescale units, specifies the track's length, enabling synchronization with other tracks. These elements allow the player to position and render the track appropriately within the overall movie.[13] Within the 'trak' container, the media atom 'mdia' further subdivides the track's media-specific details. The media header atom 'mdhd' within 'mdia' provides timing information, including the media's creation and modification times, duration in media timescale units, timescale (samples per second, a 32-bit integer), and language code (a 16-bit ISO 639-2 value for internationalization). It also includes a predefined field for quality, though this is often unused in modern implementations. Complementing this, the handler reference atom 'hdlr' identifies the type of media and the component responsible for processing it, with fields for the handler type (e.g., 'mhlr' for media handlers), component subtype (e.g., 'vide' for video, 'soun' for sound, or 'text' for text), manufacturer code, and a human-readable name as a Pascal string. Together, 'mdhd' and 'hdlr' establish the media's temporal framework and processing requirements, ensuring compatibility with QuickTime's component architecture.[13][3] At the heart of track-level organization lies the sample table atom 'stbl', a container within the media information atom 'minf' (itself under 'mdia') that describes how to access, time, and interpret individual media samples—discrete units of data like video frames or audio packets. The 'stbl' atom decomposes the track's samples into tables that facilitate efficient decoding, seeking, and random access, particularly important for compressed media where not all samples are independently decodable. Its key subatoms include:- Time-to-sample atom ('stts'): Maps sample numbers to their durations in the media timescale, consisting of a version/flags header, entry count (32-bit), and an array of pairs (sample count and duration per group of identical-duration samples). This allows cumulative time calculation to locate a sample by timestamp.
- Sync sample atom ('stss'): Lists keyframe (sync) sample numbers (32-bit integers) that begin new decoding units, omitting dependent frames to reduce file size; if absent, all samples are treated as sync samples. This is crucial for seeking in compressed video.
- Sample-to-chunk atom ('stsc'): Maps samples to storage chunks (groups of consecutive samples), with entries specifying the first chunk number, samples per chunk, and sample description index for each group. Chunks optimize I/O by bundling data.
- Sample size atom ('stsz'): Defines individual or uniform sample sizes in bytes; a uniform size field (0 for variable) or an entry count followed by per-sample sizes enables precise data extraction without scanning.
- Chunk offset atom ('stco'): Provides file offsets (32-bit or 64-bit in 'co64' variant) for each chunk, allowing direct jumps to sample data in the 'mdat' container.
Relations to Other Formats
Compatibility and Interchange with MP4
The MP4 file format serves as a subset of the QuickTime atom-based structure, where MP4 refers to these building blocks as "boxes" while retaining identical core elements such as the 'moov' atom for movie-level metadata and the 'trak' atom for individual tracks containing media data. This shared foundation, derived from the QuickTime File Format (QTFF), enables high compatibility between the two, with MP4 defined under ISO/IEC 14496-14 as an application of the broader ISO Base Media File Format (ISOBMFF).[1] Interchange between QuickTime (.mov) and MP4 (.mp4) files is facilitated by adding the 'ftyp' file type compatibility atom to a QuickTime file, which declares compatible brands (e.g., 'mp41' for MP4 version 1 or 'isom' for ISO BMFF compliance) and allows the file to be parsed and played by MP4-supporting software without altering the underlying media streams. However, challenges arise from structural differences: QuickTime's design permits free-form, proprietary atoms that parsers can skip for forward compatibility, while both support forward compatibility by skipping unknown atoms/boxes, MP4's ISO compliance requires precise box ordering and metadata placement to ensure interoperability across diverse systems. For instance, multichannel audio support for up to 24 channels was introduced in QuickTime 7 in 2005, a capability later integrated into MP4 through amendments to ISO/IEC 14496-3, which now supports configurations exceeding 48 channels in advanced profiles.)[3][16] QuickTime tools, including legacy versions of QuickTime Pro, enable passthrough export to MP4 format, which repackages the original video and audio streams into an MP4 container without re-encoding, preserving bit-for-bit quality and minimizing processing time for conversions. Broader ecosystem support highlights MP4's emphasis on hardware-accelerated decoding in consumer devices and browsers, contrasted with QuickTime's traditional reliance on software-based rendering in Apple environments, though contemporary cross-platform players like VLC ensure bidirectional readability for compatible content. File handling further aids interchange, as .mov extensions are frequently ignored by players in favor of content inspection, treating qualifying QuickTime files as de facto MP4 equivalents.[17]Basis for ISO Base Media and Derivatives
The QuickTime File Format (QTFF) provided the foundational atom-based structure for the ISO Base Media File Format (ISOBMFF), formalized as ISO/IEC 14496-12, which organizes timed media data into extensible boxes (equivalent to QuickTime atoms) to support fragmented files and progressive downloading for streaming use cases. This design enables the encapsulation of diverse media types, including video, audio, and metadata, in a manner compatible with network delivery protocols, extending QuickTime's original capabilities for broader interoperability. Several derivative formats build directly on ISOBMFF, incorporating QuickTime-derived atoms with domain-specific extensions. The 3GPP file format (3GP), defined in 3GPP TS 26.244, adapts ISOBMFF for mobile multimedia streaming and storage, adding support for 3G-specific features like adaptive streaming hints while retaining the core track and sample organization. Likewise, the Motion JPEG 2000 file format (MJ2), outlined in ISO/IEC 15444-3, uses ISOBMFF as its container to package sequences of JPEG 2000 codestreams with timing information, employing extended atoms for image track management in archival and scientific applications.[18] The High Efficiency Image Format (HEIF), specified in ISO/IEC 23008-12, leverages ISOBMFF's box structure with additional atoms to store still images, bursts, and animations, optimizing for compression efficiency in consumer devices.[19] Apple operates the MP4 Registration Authority (mp4ra.org), which oversees the assignment of four-character code-points for codecs and brands in ISOBMFF-derived formats, including 'avc1' for H.264/AVC video compression, ensuring consistent identification across implementations.[20] A notable evolution in ISOBMFF beyond classic QuickTime is the introduction of fragmentation boxes like 'sidx' (Segment Index) and 'ssix' (Subsegment Index), which enable low-latency adaptive streaming in protocols such as MPEG-DASH by dividing media into self-contained segments with indexed access points, unlike QuickTime's monolithic movie header. In broadcast environments, QuickTime atoms appear within MXF (Material Exchange Format) wrappers to embed metadata such as color volume information (e.g., MDCV and CLLI atoms), facilitating professional video workflows compliant with SMPTE standards for ultra-high-definition production and delivery.Extensions and Usage
Supported Codecs and Track Types
The QuickTime File Format supports a variety of video and audio codecs, identified by four-character codes (FourCC) within media tracks, enabling storage and playback of multimedia content.[3] These codecs are defined in sample description atoms, which specify parameters essential for decoding, such as compression algorithms and format details. Native support focuses on codecs optimized for Apple's ecosystem, with legacy options for compatibility and modern ones for high-quality production.[21] Video codecs in QuickTime files include both compressed and uncompressed formats, with prominent examples like H.264 (AVC) using the 'avc1' FourCC for efficient, high-definition encoding suitable for streaming and storage.[22] H.263 ('h263') provides basic video compression for lower-bandwidth applications, while Sorenson Video 3 ('SVQ3') offers scalable quality for web delivery.[21] Professional workflows leverage Apple ProRes ('apcn' for the 422 Standard variant), a high-bit-depth codec designed for post-production with minimal compression artifacts.[23] Legacy support includes Cinepak ('cvid'), a vector-quantized codec from the 1990s optimized for CD-ROM playback.[3]| Video Codec | FourCC | Key Characteristics |
|---|---|---|
| H.264 (AVC) | 'avc1' | Block-based compression; supports up to 8K resolution and progressive/interlaced scanning.[21] |
| H.263 | 'h263' | Low-complexity video for mobile and video conferencing.[21] |
| Sorenson Video 3 | 'SVQ3' | Three-pass encoding for variable bitrate; common in early online video.[21] |
| Apple ProRes 422 | 'apcn' | Intra-frame codec; 10-bit color depth for editing.[23] |
| Cinepak | 'cvid' | Inter-frame compression; limited to 8-bit color.[3] |
| Audio Codec | FourCC | Key Characteristics |
|---|---|---|
| AAC | 'mp4a' | Perceptual coding; supports stereo to 5.1 channels.[21] |
| PCM (little-endian) | 'sowt' | Uncompressed; variable sample rates up to 96 kHz.[3] |
| MP3 | 'mp3 ' | Layer III; integrated for legacy playback.[3] |
| Apple Lossless | 'alac' | Lossless; compresses to 40-60% of original size.[21] |