Introduction to Container Formats |
A container format is a file format that
can contain various types of data, compressed in a manner of
standardized codecs. The container file is simply used to identify and
interleave the different data types inside it.
Advanced container formats such as Ogg
and MKV can support audio, video, subtitles, chapters, and meta-data
(tags), along with the synchronization information needed for
playback.
The most popular multimedia containers are:
-
AVI (standard
Microsoft Windows container)
-
MOV (standard QuickTime container)
-
MP4 (standard container for the MPEG-4 multimedia portfolio)
-
Ogg (standard container for Xiph.org codecs)
-
Matroska (not standard for any
codec or system, but it is an open standard)
-
ASF (standard container for Microsoft WMA and WMV)
-
RealMedia (standard container for RealVideo and RealAudio)
The differences between various container formats arise from five main
issues:
-
Popularity; how widely supported a container is. This is the reason
that the AVI format is still the most popular format.
-
Overhead. This is the difference in file-size between two files
with the same content in a different container. For a two-hour film,
when in AVI, the file may be up to 10MB larger than when in Matroska.
-
Support for advanced codec functionality. Older formats such as
AVI do not support new codec features like B-frames, VBR audio, VFR
natively, although the format may be tweaked to add support, creating
compatibility problems.
-
Support for advanced content, such as chapters, subtitles, meta-tags,
user-data.
-
Support of streaming media
Below in this page you can see a full comparative table between several container formats.
|
Features Comparison
|
|
AVI |
MP4 |
OGG |
MKV |
ASF |
Standard owner |
Microsoft |
MPEG |
Xiph.org |
Matroska.org |
Microsoft |
B-frames support |
by tweaks |
Yes |
Yes |
Yes |
Yes |
VBR audio |
Yes* |
Yes |
Yes |
Yes |
Yes |
Variable frame rate |
No |
Yes |
No |
Yes |
No |
Chapters |
No |
No |
Yes |
Yes |
No |
Subtitles |
No |
ttxt |
Ogg Writ |
Anything |
No |
Streamable |
No |
Yes |
Yes |
Yes |
Yes |
*
ACM cannot
handle VBR audio streams in AVI files. Thus, software using ACM (Audio
Compression Manager) to read audio from AVI files will not be able to
handle VBR audio streams correctly, even though such files are
compliant to the AVI file specification. This is a limitation of the
ACM, not of the AVI file format. |
|
AVI
|
Audio-Video Interleave (AVI) is a
multimedia container format introduced by Microsoft in 1992, as part
of the Video for Windows technology. These files contain both audio
and video data in a standard container that allows simultaneous
playback. Most AVI files also use the file format extensions developed
by the Matrox OpenDML group in February 1996. These files are
supported by Microsoft, and are known unofficially as 'AVI 2.0'.
|
MOV
|
A QuickTime MOV file contains one
or more tracks, each of which store a particular type of data, such as
audio, video, effects, or subtitles. Each track in turn contains track
media, either the digitally encoded media stream (using a specific
codec such as Cinepak, Sorenson codec, MP3, JPEG, DivX, or PNG) or a
data reference to the media stored in another file or elsewhere on a
network. It also has an 'edit list' that indicates what parts of the
media to use.
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 formats such as AIFF DV,
MP3, MPEG-1, and AVI.
|
MP4
|
MPEG-4 Part 14 or MP4 is a
container file format specified as a part of the ISO/IEC MPEG-4
international standard. It is used to store media types defined by the
ISO/IEC Moving Picture Experts Group, and can be used to store other
media types as well.
MP4 allows streaming over the internet.
It also allows multiplexing of multiple video and audio streams in one
file, variable frame- and bit-rates, subtitles and still images.
|
Ogg
|
Ogg Media Container is developed
by Xiph.org as the
framework of a larger initiative aimed at developing a set of
components for the coding and decoding of multimedia content which are
both freely available and freely re-implementable in software.
The term Ogg often incorrectly refers to
the Vorbis audio codec. Other prominent components of Ogg are its
video codec Theora, and the speech audio compression format, Speex.
If you
are wondering about the OGM format, refer to
this page
for detailed information. DivXLand.org suggests to use the Matroska
container, since OGM is no longer developed.
|
Matroska |
Matroska aims to be the standard for multimedia
container formats. It incorporates features you would expect from a modern
container format, like:
The
Matroska file extensions are:
-
.mkv: generally video files, as
well those containing audio (movies) or video only.
-
.mka: audio only files, can
contain any supported audio compresion format, such as MP2, MP3,
Vorbis, AAC, AC3, DTS, PCM.
-
.mks: a so called 'elementary'
matroska stream containing any subtitles stream.
To open
Matroska files, you need to install either the
DivX Total Pack or the
Matroska
Pack filter. For extended information regarding the Matroska container
format, visit its website.
|
ASF
|
Advanced Systems Format (formerly
Advanced Streaming Format) is Microsoft's proprietary digital audio
and video container format, especially designed for streaming media.
ASF is part of the Windows Media framework.
The format does not specify how the video
or audio should be encoded, but instead just specifies the structure
of the video/audio stream. What this means is that ASF files can be
encoded with basically any audio/video codec and still would be in ASF
format. This is similar to the function performed by the QuickTime,
AVI, or Ogg formats.
The most common filetypes contained
within an ASF file are Windows Media Audio (WMA) and Windows Media
Video (WMV).
|
RealMedia
|
RealMedia is a multimedia container
format created by RealNetworks.
It is typically used in conjunction with RealVideo and RealAudio
compression and is popular for streaming content over the internet.
RM content can be played with RealPlayer,
or with any DirectShow based player by installing third party filters
such as RealAlternative.
|
Questions? Comments?
|
|
If you have any questions or need support
regarding this guide or article, don't hesitate to ask at the
DivXLand.org
forum personally. |

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