MPEG-1 video is used by the Video CD (VCD) format and less commonly by the DVD-Video format. At present MPEG-1 is the most compatible format in the MPEG family; it is playable in almost all computers and VCD/DVD players. The quality at standard VCD resolution and bitrate is roughly that of a VHS tape.
MPEG-1 video was originally designed with a goal of achieving acceptable video quality at 1.5M bit/second data rates and 352x240 (29.97 frame per second) / 352x288 (25 frame per second) resolution. While MPEG-1 applications are often low resolution and low bitrate, the standard allows any resolution less than 4095x4095.
The video information is encoded using a technique called DCT (Discrete Cosine Transform).
One big disadvantage of MPEG-1 video is that it supports only progressive pictures. This deficiency helped prompt development of the more advanced MPEG-2.
MPEG-2 was the second of several standards developed by the Motion Pictures Expert Group (MPEG) and is an international standard (ISO/IEC 13818). It is widely used around the world to specify the format of the digital television signals that are broadcast by terrestrial (over-the-air), cable, and direct broadcast satellite TV systems. It also specifies the format of movies and other software that are distributed on DVD and similar disks. The standard allows text and other data, e.g., a software guide for TV viewers, to be added to the video and audio data streams. TV stations, TV receivers, DVD players, and other equipment are all designed to this standard.
MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It specifies that the raw frames be compressed into three kinds of frames: I(ntra-coded)-frames, P(redictive-coded)-frames, and B(idirectionally predictive-coded)-frames. P-frames and B-frames might follow an I-frame like this, IBBPBBPBBPBB(I), to form a GOP (Group Of Pictures).
MPEG-2 supports both interlaced and progressive video types.
With progressive scan, an image is captured, transmitted and displayed in a path similar to text on a page: line by line, from top to bottom. The interlaced scan pattern in a CRT display completes such a scan too, but only for every second line. Then process is repeated again, only this time starting at the second row, in order to fill in those particular gaps left behind while performing the first progressive scan on alternate rows only.
While interlace can improve the picture quality of a video transmission without consuming any extra bandwidth, it can cause flicker and various kinds of distortion. It can't be used for LCD, micromirror (DLP), or plasma displays, which are inherently progressive scan. The advantages of progressive scan are: simpler video editing equipment, easier compression, subjectively increased vertical resolution, no flickering of narrow horizontal patterns.
MPEG-2 also introduces new audio encoding methods. These are
The DVD (Digital Versatile Disc) standard uses MPEG-2 video, but imposes some restrictions:
- low bitrate encoding with halved sampling rate (MPEG-1 Layer 1/2/3 LSF)
- multichannel encoding with up to 5.1 channels
- MPEG-2 AAC
A major selling point of DVD Video is that its storage capacity allows for a wide variety of extra features in addition to the feature film itself. This can include audio commentary that is timed to the film sequence, documentary features, unused footage, trivia text commentary, simple games and film shorts.
- Allowed Resolutions
- 720 õ 480, 704 õ 480, 352 õ 480, 352 õ 240 pixel (NTSC)
- 720 õ 576, 704 õ 576, 352 õ 576, 352 õ 288 pixel (PAL)
- Allowed Aspect ratio (Display AR)
- (2.21:1 is often listed as a valid DVD aspect ratio, but is actually just a 16:9 image with the top and bottom of the frame masked in black)
- Allowed Frame rates
- 29.97 frame/s (NTSC)
- 25 frame/s (PAL)
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- Video peak 9.8 Mb/s
- Total peak 10.08 Mb/s
- Minimum 300 Kbit/s
Other extras that can be included on DVDs (extra to the main audio/visual software) are motion menus, still pictures, up to 32 selectable subtitles, seamless branching for multiple storylines, 9 camera angles. And also additional DVD-ROM / data files that only can be read by computer DVD drives.
A VOB file (Versioned Object Base) is a container format contained in DVD-Video media. It contains the actual video, audio, subtitle and menu contents in stream form.
VOB files are encoded very much like standard MPEG-2 files. If the extension is changed from .vob to .mpg or .mpeg, the file is still readable and continues to hold all information, although most MPEG-2-capable players don't support subtitle tracks. In order to burn the VOB files to a DVD±R disc, other standard DVD-Video files are needed as well, including IFO and BUP files.
IFO is a DVD InFOrmation file that stores information about chapters, subtitles and audio tracks.
The BUP file is an identical BackUP of a file of the same name which has the extension IFO.
AVI (Audio Video Interleave) is a multimedia container format introduced by Microsoft in November 1992 as part of the Video for Windows technology. AVI files contain both audio and video data in a standard container that allows simultaneous playback. Like DVDs, AVI files support multiple audio and video streams, although these features are rarely used. Most commonly used video codecs that use AVI structure are M-JPEG, XVid and DivX.
AVI is considered by many to be an outdated container format. There is significant overhead when used with popular MPEG-4 codecs, increasing file size more than necessary. The container has no native support for codecs' modern features like B-Frames.
However, despite its limitations and the availability of more modern container formats (Matroska, Ogg and MP4), AVI remains popular among file-sharing communities. This is probably due to its high compatibility with existing video editing and playback software like VirtualDub and Windows Media Player.
MP3 (MPEG-1 Audio Layer 3) is a popular digital audio encoding and lossy compression format. It provides a representation of pulse-code modulation-encoded audio in much less space than straightforward methods, by using psychoacoustic models to discard components less audible to human hearing, and recording the remaining information in an efficient manner. Because MP3 is a lossy format, it is able to provide a number of different options for its bit rate. Typically, rates chosen are between 128 and 320 kilobit per second. By contrast, uncompressed audio as stored on a compact disc has a bit rate of 1411.2 kbit/s (16 bits/sample x 44100 samples/second x 2 channels).
MP3 audio can be compressed with several different bit rates, providing a range of tradeoffs between data size and sound quality.
Bit rates available in MPEG-1 Layer 3 are 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256 and 320 kbit/s, and the available sampling frequencies are 32, 44.1 and 48 kHz. 44.1 kHz is almost always used (coincides with the sampling rate of compact discs), and 128 kbit/s has become the de facto "good enough" standard, although 192 kbit/s is becoming increasingly popular over peer-to-peer file sharing networks. MPEG-2 and the (unofficial) MPEG-2.5 include some additional bit rates: 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 kbit/s; while providing lower sampling frequencies (8, 11.025, 12, 16, 22.05 and 24 kHz).
There are several limitations inherent to the MP3 format that cannot be overcome by using a better encoder. In technical terms, MP3 is limited in the following ways:
Newer audio compression formats such as Vorbis and AAC no longer have these limitations.
Nevertheless, a well-tuned MP3 encoder can perform competitively even with these restrictions.
- Bitrate is limited to a maximum of 320 kbit/s (while some encoders can create higher bitrates, there is little-to-no support for these higher bitrate mp3s)
- Time resolution can be too low for highly transient signals, causing some smearing of percussive sounds
- Frequency resolution is limited by the small long block window size, decreasing coding efficiency
- No scale factor band for frequencies above 15.5/15.8 kHz
- Joint stereo is done on a frame-to-frame basis
- Encoder/decoder overall delay is not defined, which means lack of official provision for gapless playback. However, some encoders such as LAME can attach additional metadata that will allow players that are aware of it to deliver gapless playback.
MP3's extreme popularity makes it secure in its dominant position for the near future, with support from a huge range of software and hardware, including portable MP3 players and even some DVD and CD players. The large MP3 collections that many individuals have amassed will also ensure its longevity.
WMV (Windows Media Video) is a multimedia format developed and controlled by Microsoft. It is used for both streaming and downloading content via the Internet. WMV files have audio and video streams. WMV Format is designed to handle all types of video content. The files can be highly compressed and can be delivered as a continuous flow of data.
WMV files can be of any size and can be compressed to match many different bandwidths (connection speeds). The WMV format is a derivative of the MPEG-4 format. However, it's more efficient than MPEG-4 in encoding video and, while similar to the ASF format (Microsoft's Advanced Streaming Format), it allows for decreased file size. Using WMV is an excellent way to get file sizes down to reasonable levels while retaining watchable quality.
WMV format allows to encode the same content to several different streams, each with a different bit rate. Then you can configure the streams so that they are mutually exclusive. This enables you to create a single file that can be streamed to users with different bandwidths. This feature is called multiple bit rate, or MBR.
WMV is generally packed into an ASF container format. It can also be put into AVI or Matroska containers. The resulting files may be named .avi if it is an AVI-contained file, or .wmv or .asf if it is an ASF file, or .mkv if it is an MKV file. WMV can be stored in an AVI file when using the WMV9 VCM codec implementation. One common way to encode WMV in AVI is to use the VirtualDub encoder. Microsoft's Windows Media Player for the Mac does not support all WMV encoded files since it supports only the ASF file container. More files can be played with Flip4Mac and QuickTime or MPlayer for Mac OS X.
When encapsulated in ASF file format, WMV can support DRM (Digital Rights Management) protected content.
Besides being a popular codec for distributing video on the Internet, WMV is also used to distribute high definition video on standard DVDs in a format Microsoft has branded as WMV HD. This WMV HD content can be played back on computers or compatible DVD players.
FLV (Flash Video) is a proprietary file format used to deliver video over the Internet using Adobe Flash Player (formerly known as Macromedia Flash Player) version 6, 7, 8, or 9. FLV content may also be embedded within SWF files. Notable users of the FLV format include YouTube, Google Video, Reuters.com and MySpace.
Flash Video is viewable on most operating systems, via the widely available Adobe Flash Player and web browser plugin, or one of several third-party software such as Media Player Classic (with the ffdshow codecs installed), MPlayer, or VLC media player.
Commonly FLV files contain video bit streams which are a variant of the H.263 video standard, under the name of Sorenson Spark. Flash Player 8 and newer revisions support the playback of On2 TrueMotion VP6 video bit streams. On2 VP6 can provide a higher visual quality than Sorenson Spark, especially when using lower bit rates. On the other hand it is computationally more complex and therefore will not run as well on certain older system configurations.
Audio in FLV files is usually encoded as MP3.
MOV (MOVie) files are the standard QuickTime video and animation format developed by Apple Computer. QuickTime is built into the Macintosh operating system and is used by most Mac applications that include video or animation. PCs can also run files in QuickTime format, but they require a separate (free) downloadable software.
A QuickTime file functions as a multimedia container file that contains one or more tracks, each of which store a particular type of data, such as audio, video, effects, or text (for subtitles, for example). 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. Other later-developed media container formats such as Microsoft's Advanced Streaming Format or the open source Ogg and Matroska containers lack this abstraction, and require all media data to be rewritten after editing.
MPEG-4 is a standard used primarily to compress audio and video (AV) digital data. Introduced in late 1998, it is the designation for a group of audio and video coding standards and related technology agreed upon by the ISO/IEC Moving Picture Experts Group. The uses for the MPEG-4 standard are web and CD distribution, conversation, and broadcast television, all of which benefit from compressing the AV stream.
MPEG-4 absorbs many of the features of MPEG-1 and MPEG-2 and other related standards, adding new features such as (extended) VRML support for 3D rendering, object-oriented composite files (including audio, video and VRML objects), support for externally-specified Digital Rights Management and various types of interactivity. AAC (Advanced Audio Codec) was standardized as an adjunct to MPEG-2 (as Part 7) before MPEG-4 was issued.
Most of the features included in MPEG-4 are left to individual developers to decide whether to implement them. This means that there are probably no complete implementations of the entire MPEG-4 set of standards. To deal with this, the standard includes the concept of "profiles" and "levels", allowing a specific set of capabilities to be defined in a manner appropriate for a subset of applications.
3GP (3rd Generation Phone) is a multimedia container format defined by the 3GPP (Third Generation Partnership Project) for use on 3G mobile phones.
3GP represents a simplified version of the MPEG-4 Part 14 (MP4) container format, designed to decrease storage and bandwidth requirements in order to accommodate mobile phones. It stores video streams as MPEG-4 or H.263 or H.264, and audio streams as AMR-NB or AAC-LC. A 3GP file is always big-endian, storing and transferring the most significant bytes first. It also contains descriptions of image sizes and bitrate.
There are two different standards for this format:
Both are based on MPEG-4 and H263 video, and AAC or AMR audio.
- 3GPP (for GSM Based Phones, may have filename extension .3gp)
- 3GPP2 (for CDMA Based Phones, may have filename extension .3g2)
|Publication date: 06.01.2007