What is ftypisom?

Which is as follows: ""ftypisom isomiso2avc1mp41 free zmdat }e !. MPEG-4 Part 14 or MP4 is a digital multimedia format most commonly used to store video and audio, but can also be used to store other data such as subtitles and. ftypisom isomiso2avc1mp41 freexl€umdat ÿÿÿ ÜEé½æÙH·–,Ø Ù#îïx264 - core 148 r2597M e86f3a1 - H.

The ISO base media file format (ISOBMFF) is a container file format that defines a general structure for files that contain time-based multimedia data such as video and audio. It is standardized in ISO/IEC 14496-12, a.k.a. MPEG-4 Part 12, and was formerly also published as ISO/IEC 15444-12, a.k.a. JPEG 2000 Part 12.

It is designed as a flexible, extensible format that facilitates interchange, management, editing and presentation of the media. The presentation may be local, or via a network or other stream delivery mechanism. The file format is designed to be independent of any particular network protocol while enabling support for them in general.

The format has become very widely used for media file storage and as the basis for various other media file formats (e.g. the MP4 and 3GP container formats), and its widespread use was recognized by a Technology & Engineering Emmy Award presented on 4 November 2021 by the National Academy of Television Arts and Sciences.

The ISO base media file format is directly based on Apple's QuickTime container format. It was developed by MPEG (in ISO/IEC JTC 1/SC 29, originally Working Group 11 MPEG, currently Working Group 3 MPEG Systems). The first MP4 file format specification was created on the basis of the QuickTime format specification published in 2001. The MP4 file format known as "version 1" was published in 2001 as ISO/IEC 14496-1:2001, as revision of the MPEG-4 Part 1: Systems. In 2003, the first version of the MP4 file format was revised and replaced by MPEG-4 Part 14: MP4 file format (ISO/IEC 14496-14:2003), commonly known as MPEG-4 file format "version 2".

The MP4 file format was generalized into the ISO base media file format (ISO/IEC 14496-12:2004 or ISO/IEC 15444-12:2004), which defines a general structure for time-based media files. It is used as the basis for other file formats in the family such as MP4, 3GP, and Motion JPEG 2000).

Historically, the text was also published as ISO/IEC 15444-12 (JPEG 2000 Part 12), although the JPEG 2000 version of the standard was withdrawn in January 2017 since it was redundant with the MPEG-4 publication.

The ISO base media file format is designed as an extensible file format. A list of all registered extensions for the ISO base media file format is published on the official registration authority website, www.mp4ra.org. The registration authority for code-points (identifier values) in "MP4 Family" files is Apple Inc. and it is named in Annex D (informative) in MPEG-4 Part 12. Codec designers should register the codes they invent, but the registration is not mandatory and some of invented and used code-points are not registered. When someone is creating a new specification derived from the ISO base media file format, all the existing specifications should be used both as examples and a source of definitions and technology. If an existing specification already covers how a particular media type is stored in the file format (e.g. MPEG-4 audio or video in MP4), that definition should be used and a new one should not be invented.

MPEG has standardized a number of specifications extending the ISO base media file format: The MP4 file format (ISO/IEC 14496-14) defined some extensions over ISO base media file format to support MPEG-4 visual/audio codecs and various MPEG-4 Systems features such as object descriptors and scene descriptions. The MPEG-4 Part 3 (MPEG-4 Audio) standard also defined storage of some audio compression formats. Storage of MPEG-1/2 Audio (MP3, MP2, MP1) in the ISO base media file format was defined in ISO/IEC 14496-3:2001/Amd 3:2005. The Advanced Video Coding (AVC) file format (ISO/IEC 14496-15) defined support for H.264/MPEG-4 AVC video compression. The High Efficiency Image File Format (HEIF) is an image container format using the ISO base media file format as the basis. While HEIF can be used with any image compression format, it specifically includes the support for HEVC intra-coded images and HEVC-coded image sequences taking advantage of inter-picture prediction.

Some of the above-mentioned MPEG standard extensions are used by other formats based on ISO base media file format (e.g. 3GP). The 3GPP file format (.3gp) specification also defined extensions to support H.263 video, AMR-NB, AMR-WB, AMR-WB+ audio and 3GPP Timed Text in files based on the ISO base media file format. The 3GPP2 file format (.3g2) defined extensions for usage of EVRC, SMV or 13K (QCELP) voice compression formats. The JPEG 2000 specification (ISO/IEC 15444-3) defined usage of Motion JPEG 2000 video compression and uncompressed audio (PCM) in the ISO base media file format (.mj2). The "DVB File Format" (.dvb) defined by DVB Project allowed storage of DVB services in the ISO base media file format. It allows the storage of audio, video and other content in any of three main ways: encapsulated in a MPEG transport stream, stored as a reception hint track; encapsulated in an RTP stream, stored as a reception hint track or stored directly as media tracks. The MPEG-21 File Format (.m21, .mp21) defined the storage of an MPEG-21 Digital Item in the ISO base media file format, with some or all of its ancillary data (such as movies, images or other non-XML data) within the same file. The OMA DRM Content Format (.dcf) specification from Open Mobile Alliance defined the content format for DRM protected encrypted media objects and associated metadata. There are also other extensions, such as ISMA ISMACryp specification for encrypted/protected audio and video, G.719 audio compression specification, AC3 and E-AC-3 audio compression, DTS audio compression, Dirac video compression, VC-1 video compression specification and others, which are named on the MP4 Registration authority's website.

There are some extensions of the ISO base media file format that were not registered by the MP4 Registration authority. Adobe Systems introduced the F4V file format for Flash Video in 2007 and said it is based on the ISO base media file format. The F4V file format was not registered by the MP4 registration authority, but the F4V technical specification is publicly available. This format can contain H.264 video compression and MP3 or AAC audio compression. In addition, F4V file format can contain data corresponding to the ActionScript Message Format and still frame of video data using image formats GIF, JPEG and PNG. Microsoft Corporation announced a file format based on the ISO base media file format in 2009 called ISMV (Smooth Streaming format), also known as Protected Interoperable File Format (PIFF). As announced, this format can for example contain VC-1, WMA, H.264 and AAC compression formats. Microsoft published a Protected Interoperable File Format (PIFF) specification in 2010. It defined another usage of multiple encryption and DRM systems in a single file container. PIFF brand was registered by the MP4 registration authority in 2010. Some extensions used by this format (e.g. for WMA support) were not registered. Usage of the WMA compression format in the ISO base media file format was not publicly documented.

The ISO base media file format includes timing, structure, and media information for timed sequences of media data, such as audio-visual presentations. The file structure is object-oriented. A file can be decomposed into basic objects very simply, and the structure of the objects is implied from their type.

Files conforming to the ISO base media file format are formed as a series of objects, called "boxes". All data is contained in boxes, and there is no other data within the file. This includes any initial signature required by the specific file format. The "box" is an object-oriented building block defined by a unique type identifier and length. It was called an "atom" in some specifications (e.g. the first definition of the MP4 file format).

A presentation (motion sequence) may be contained in several files. All timing and framing (position and size) information must be in the ISO base media file, and the ancillary files may essentially use any format.

In order to identify the specifications to which a file based on the ISO base media file format complies, "brands" are used as identifiers in the file format. These are set in a box named file type box ("ftyp"), which must be placed in the beginning of the file. It is somewhat analogous to the so-called fourcc code, used for a similar purpose for media embedded in AVI container format. A brand might indicate the type of encoding used, how the data of each encoding is stored, constraints and extensions that are applied to the file, the compatibility, or the intended usage of the file. Brands are a printable four-character codes. A file type box contains two kinds of brands. One is "major_brand", which identifies the specification of the best use for the file. It is followed by "minor_version", an informative 4-byte integer for the minor version of the major brand. The second kind of brand is "compatible_brands", which identifies multiple specifications to which the file complies. All files shall contain a file type box, but for compatibility reasons with an earlier version of the specification, files may be conformant to ISO/IEC base media file format and not contain a file type box. In that case they should be read as if they contained an ftyp with major and compatible brand "mp41" (MP4 v1 – ISO 14496-1, Chapter 13). Some in-use brands (ftyps) are not registered and can be found on some webpages.

A multimedia file structured upon ISO/IEC base media file format may be compatible with more than one concrete specification, and it is therefore not always possible to speak of a single "type" or "brand" for the file. In this regard, the utility of the Multipurpose Internet Mail Extension type and file name extension is somewhat reduced. In spite of that, when a derived specification is written, a new file extension will be used, a new MIME type and a new Macintosh file type.

The ISO/IEC base media file format supports streaming of media data over a network as well as local playback. A file that supports streaming includes information about the data units to stream (how to serve the elementary stream data in the file over streaming protocols). This information is placed in additional tracks of the file called "hint" tracks. Separate "hint" tracks for different protocols may be included within the same file. The media will play over all such protocols without making any additional copies or versions of the media data. Existing media can be easily made streamable for other specific protocols by the addition of appropriate hint tracks. The media data itself need not be reformatted in any way. The streams sent by the servers under the direction of the hint tracks, need contain no trace of file-specific information. When the presentation is played back locally (not streamed), the hint tracks may be ignored. Hint tracks may be created by an authoring tool or may be added to an existing file (presentation) by a hinting tool. In media authored for progressive download, the moov box, which contains the index of frames, should precede the movie data mdat box.

This guide is an introduction and a quick dive into the MP4 file format, also known as the ISO Base Media File Format (ISO-BMFF MPEG-4 Part 14). Fancy name, I know.

I won't go into the playback details in this guide, but more of the MP4 byte format commonly known as the MP4 Box Structure.

The MPEG-4 Part 14 (MP4) is one of the most common container formats for video and has an extension of .mp4. You may already know of other container formats, such as wav, mov, mp3 or more recently webm. A container just "contains" the video or audio track, or both. It can also support embedded subtitle tracks too.

MP4 is an extension of the ISO Base Media File Format (ISOBMFF, MPEG-4 Part 12), which is a format designed to contain timed media information.

The ISO-BMFF format is directly based on QuickTime, therefore the MP4 is essentially identical to the QuickTime file format.

In order to fully understand the MP4 structure, you'll need to obtain a copy of the ISO documents:

A Google search should result in a few resources to get a copy of the PDF.

Since MP4 is a container format, it doesn't actually handle the decoding of the video and audio streams, it just contains them as tracks along with their metadata.

A container can store some of the following information:

This is all the information a player needs to decode and play the content.

At a high-level, this is what an MP4 structure typically looks like:

The MP4 byte structure is composed of a series of boxes, also known as "atoms", according to the QuickTime specification. Each box describes and contains data to build the MP4 container format.

Boxes typically have a four letter name, also known as a FourCC. This is the shortened version of the full box name, enough to fit into 4 bytes. This is important for when you are reading and writing boxes into or from the byte format.

Before we jump into the byte structure details, here is a more technical view of the MP4 box tree, compared to the high-level view above:

This is just a simplified view. However, there are many more boxes defined in the MP4 specification.

An MP4 "Box" contains just enough information to read and parse the box name, size and data.

Each of these boxes have a different purpose, containing a bit of information and details on a specific piece of data. Some boxes describe the file type, and others can describe codec detail, picture resolution, frame rate, duration, sample sizes and more. There's also boxes containing the encoded video and audio data too.

A box typically contains the following base information:

This is just enough information we need to know how to parse a box, along with the MP4 specification document to understand the box fields.

So let's parse our first box!

As mentioned above, the first 8 bytes of each box is known as the "Box Header", where the first 4 bytes are the size of the box, and the next 4 bytes are the box name. These are the two values you need to know to iterate and parse each box, byte by byte.

Here's a box header struct for example:

Reading the box data from each atom requires the box size, name and byte structure of each box you are parsing. You can refer to the MPEG-4 Part 14 specification for the byte structure of each known box, or just refer to some existing MP4 parsing open-source code.

According to the specification, the ftyp box has the following structure:

For example, reading the FileTypeBox (ftyp) would look something like the following (in Golang):

Going over the above:

See a minimal example: https://gist.github.com/alfg/7375aee32fda490de4bf62fbced49d2e#file-mp4_example-go

If you were to open the mp4 into a hex editor, it would look something like this for the ftyp box:

Now that we've read the ftyp box, we can move on to the next box header, which happens to be the moov box:

The moov box contains a nested mvhd box, so we also need to define mvhd too:

See the example with moov and mvhd box included: https://gist.github.com/alfg/7375aee32fda490de4bf62fbced49d2e#file-mp4_example_2-go

Now that we've parsed 3 boxes, hopefully you have an idea on how to implement more. The process is iterative when using a reader:

For a more complete example of reading MP4 boxes in Go, check out: https://github.com/alfg/mp4

I also have a more advanced MP4 reader and writer in Rust: https://github.com/alfg/mp4rs

I highly suggest some of the following tools for inspecting MP4 files:

Find me on GitHub at: https://github.com/alfg

Happy Hacking! 🎥

MPEG-4 Part 14 or MP4 is a digital multimedia format most commonly used to store video and audio, but can also be used to store other data such as subtitles and still images. MP4 allows streaming over the Internet. The only official filename extension for MPEG-4 Part 14 files is .mp4, but many have other extensions, most commonly .m4a and .m4p.

The MPEG-4 file format specification was based on the QuickTime format specification.

MP4 files consist of consecutive chunks. Each chunk has 8 byte header: 4-byte chunk size (big-endian, high byte first) and 4-byte chunk type - one of pre-defined signatures: "ftyp", "mdat", "moov", "pnot", "udta", "uuid", "moof", "free", "skip", "jP2 ", "wide", "load", "ctab", "imap", "matt", "kmat", "clip", "crgn", "sync", "chap", "tmcd", "scpt", "ssrc", "PICT".

First chunk must be of type "ftype" and has a sub-type at offset 8. MP4 defined by sub-type which must be one of values: "avc1", "iso2", "isom", "mmp4", "mp41", "mp42", "mp71", "msnv", "ndas", "ndsc", "ndsh", "ndsm", "ndsp", "ndss", "ndxc", "ndxh", "ndxm", "ndxp", "ndxs".

Iterating chunks, until unknown type is detected, we compose MP4 file.

Let's examine the sample

When inspecting sample.mp4 file's binary data using any Hex Viewer, like Active@ Disk Editor we can see it starts with a signature ftyp (hex: 66 74 79 70) at offset 4, which defines QuickTime Container File Type.

File sub-type is mmp4 (hex: 6D 6D 70 34) which points to MP4 file type. First block size is 28 (hex: 00 00 00 1C, big-endian, high byte first), size located at offset 0.

At offset 28 (hex: 1C) is located the second chunk, which has a size of 8 and type mdat (hex: 6D 64 61 74).

The next chunk is located at offset 28+8=36 (hex: 24) and has a size 303,739 (hex: 00 04 A2 7B) and type mdat (hex: 6D 64 61 74) at offset 40 (hex: 28).

The next chunk is located at offset 36 + 303,739=303,775 and has a size 6,202 (hex: 00 00 18 3A) and type moov (hex: 6D 6F 6F 76) at offset 303,779.

This is the last chunk, so total file size is 303,775+6,202=309,977 bytes.