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M
M2T, m2ts, mts

M3U
mAC3dec
Macroblock
Macrovision
MacVCD
Main Concept Encoder
Matroska, MKA, MKV, MKS
MICROMV
Mini DV
miniDVD, cDVD
MJPEG
MLP
Motion compensation and prediction
Motion Estimation
Mount Rainier
MOV
MP3
MP3 ID3 Tag, ID3
MP4
MPA, MP1, MP2
MPEG Audio
MPEG-1
MPEG-2
MPEG-3
MPEG-4
MPEG-7
MPEGInfoX
mpegproperties
MPlayerOSX
MPV, M1V, M2V
MultiAngle, Multi-Angle
Multiplex, Multiplexing, Mux, Muxing
Multisystem



M
M2T, m2ts, mts
The .mts, .m2t and .m2ts are a container file format for multiplexing audio, video and other streams. It is based on the MPEG transport stream container and is also known as BDAV MPEG-2 transport stream. This format is commonly used for high definition video on Blu-ray Disc and AVCHD and HD Camcorders. It usually contain AVC/H264 or MPEG2 video.




M3U
An .m3u file is a special type of metafile playlist that is used with MP3 files that have an .mp3 file extension. The .m3u file includes information about the location of the .m3u file on the computer and the properties of the file. An .m3u file is similar to the ASX playlist files.

If an error message occurs on play then the MP3 files may have been moved or deleted.




mAC3dec
A MAC program used to convert .ac3 files to .aiff or .mp3 files.




Macroblock
A macroblock is a portion of image that consists of 16x16 picture elements (pixels or pels).
At the macroblock layer motion compensation and prediction are performed and it's possible to change the quantisation step.
It must be noticed that, if the picture is an interlaced frame picture, the odd lines of the macroblock belong to the first field and the even lines to the second field.

Video decoding process at the macroblock layer
Decode the macroblock mode and the possible quantiser_scale_code.
If it's an Intra macroblock:
Decode the blocks which the macroblock consists of.
If it's a Non-Intra macroblock:
Decode the prediction mode and the motion vectors.
Produce the suitable prediction for the macroblock.
Decode the blocks which the macroblock consists of, obtaining the prediction errors values.
Add the prediction errors values to the prediction.




Macrovision
An analog video copy protection scheme that alters the unseen part of a video signal such that a VCR or other macrovision enabled device may not record the video signal properly. There are several types:
- Automatic Gain Control
- 2-line color stripe
- 4-line color stripe

Symptoms of this include picture fading in and out or color banding of the signal.




MacVCD
A VCD player available for the Mac OS X platform




Main Concept Encoder
A very good mid range (in cost) mpeg encoder. Often found as the encoding engine in other products (Vegas Video and Adobe Premiere are some such applications that Main Concept).

Main Concept also makes other video applications such as a compositing program and soon to be released full featured video editing program and low end video editor.

Main Concept also has a very high quality DV codec
http://www.mainconcept.com/




Matroska, MKA, MKV, MKS
A new video and audio container format similiar to AVI but with several new features like support for OGG audio, Variable Framerate Video.
Matroska File Formats:
.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 and soon MPC ( musepack )
.mks : a so called 'elementary' matroska stream containing any subtitles stream
For more info, see http://www.matroska.org




MICROMV
The MICROMV cassette is the smallest type of camcorder tape to date — nearly 70% smaller than already tiny Mini DV tapes — so it's no surprise that all MICROMV camcorders feature an incredibly compact form factor. MICROMV cassettes feature a built-in memory chip for conveniences like custom title storage and index thumbnails for easy access to specific scenes.




Mini DV
Mini DV is a video cassette designed for use in MiniDV digital camcorders. The picture quality of digital video (DV) recorded on a Mini DV cassette is basically identical or better to the quality of DV recorded on a Hi8 or 8mm cassette by a Digital8 camcorder. Mini DV can have up to 530 lines of video resolution for some camcorder models. However, Mini DV tapes are smaller which allows for smaller camcorders. Mini DV tapes are available in lengths of 30 and 60 minutes (plus, recording in LP mode lets you extend total recording time with a 60-minute tape to 90 minutes).




miniDVD, cDVD
miniDVD is a DVD video written onto a CD-R(W) instead of a DVD disc. miniDVD is also sometimes called cDVD. A miniDVD only fits about 15 minutes of DVD quality video on a 650 MB CD-R(W). Not many DVD players will play miniDVD - see the DVD Players miniDVD list for compatible players. DVDRhelp.com miniDVD page




MJPEG
Moving JPEG. A moving image which is made by storing each frame of a moving picture sequence in JPEG compression, then decompressing and displaying each frame at rapid speed to show the moving picture.M-JPEG does not use interframe coding as MPEG does. Sometimes called Motion JPEG.




MLP
Meridian Lossless Packing. A lossless compression technique (used by DVD-Audio) that removes redundancy from PCM audio signals to achieve a compression ratio of about 2:1 while allowing the signal to be perfectly recreated by the MLP decoder.




Motion compensation and prediction
Motion compensation and prediction are performed at the macroblock layer.
The goal of motion compensation is to provide a good prediction for the macroblock. Actually, in the macroblocks where prediction is applied, the DCT is performed to the prediction errors instead of to the image samples and more the prediction errors are low and more the entropy coding is effective. Therefore, with good predictions it's possible to have low bit rate and good quality.
In nearly still pictures it's quite easy to have very good predictions using the pixels just in the same position of those to predict, but in motion pictures it's necessary to take movements into account.

Both the coder and the decoder have two frame-memories where they store the decoded pictures used as references.
Where do the predictions come from ?
It depends on the kind of the picture.

Predictions for a P_picture
If it's a frame picture they may come from the previous I or P frame.
If it's a field picture they may come from the two I or P fields coded most recently.
Predictions for a B_picture
They may come from the previous (in display order) I or P frame as from the next (in display order) I or P frame and there may be an interpolation between predictions coming from both directions.
See also the sequence layer.

What's a motion vector ?
A motion vector is a bi-dimensional pointer that tell the decoder how much left/right and up/down, from the position of the macroblock, is located the prediction macroblock in the reference frame or field.
Motion vectors have an half-pel resolution, that means that an interpolation process is necessary to get the prediction (for MPEG-1 is also possible the simpler pel resolution selected at the picture layer). It must be noticed that the same motion vector is applied both to luminance and, after being scaled, to chrominance.

What's motion estimation ?
Motion estimation is the process, perfomed by the coder, that should find the motion vector pointing to the best prediction macroblock in a reference frame or field.
The goodness of a prediction macroblock is in general evaluated minimizing a cost function that may be the absolute error or the mean squared error. The cost function is applied to the macroblock (or a part of it), such technique is called block matching and is the most used in video coding. In general every possible prediction in a given range is evaluated, so we speak about full search. Unfortunatly the computation's complexity is proportional to the search area and can be quite heavy, and on the other hand the search area has to be wide enough to include every movement.
It must be noticed that the capability to perform a good motion estimation is a key point for the quality of a coder.

The prediction menu for frame pictures.
Frame-based prediction.
A single motion vector for the whole macroblock. It's used when movements between the two fields are unsignificant. It's the only possible choice for progressive images.
Field-based prediction.
Two different motion vectors. One for the samples belonging to the first field and one for those belonging to the second field. It's used when movements between the two fields are important.

The prediction menu for field pictures.
Field prediction.
A single motion vector for the whole macroblock. It's used when the whole area has a single movement.
16x8 prediction.
Two different motion vectors. One for the top half and one for the bottom half of the macroblock. It's used when the macroblock includes different objects with different movements and the macroblock area is to large to have a good prediction.




Motion Estimation
In video encoding, the process of analyzing previous or future frames to identify blocks that have not changed or have only changed location. Motion vectors are then stored in place of the blocks. This is very computation-intensive and can cause visual artifacts when subject to errors.




Mount Rainier
Mount Rainier is a standard that provides background formatting and defect management for storage on CD-RW and DVD+RW. This makes rewritable discs far easier to use and allows the replacement of the floppy. In the near future, native Operating System support for Mount Rainier is available. http://www.licensing.philips.com/information/mtr/gi/




MOV
QuickTime Content (.mov, .qt) - a file format developed by Apple Computer to create, edit, publish, and view multimedia files. QuickTime supports video, animation, graphics, 3D and virtual reality (VR). Sample MOV file




MP3
MP3 is an acronym for MPEG-1 (or MPEG-2) Layer 3 audio encoding (it is not an acronym for MPEG3). MP3 is a popular compression format used for audio files on computers and portable devices.

The compression in MP3 works on the basis of a "psychoacoustic model" which means that parts of the audio that human ears cannot detect are discarded by the encoder. Although this is a LOSSY process, it can yield very high quality audio files are relatively high compression rates.

A typical MP3 file encoded at 128 kbit/s (12:1 compression) is near CD quality.

MP3 audio is increasingly being used in video production coupled with various MPEG-4 video codecs like divx. The audio may be encoded with a constant or variable bitrate.




MP3 ID3 Tag, ID3
An MP3 ID3 Tag is information stored at the end of an MP3 file. The tag can contain information about the Title/Songname, Artist, Album, Year, Comment, and Genre in version 1 and also Track in version 1.1. A proposed Version 2 is out which would be extendable to include more information and picture(s). ID3.org




MP4
MP4 is a new container format, a container format allows you to combine different multimedia streams into one single file. Multimedia containers are for example the well known AVI, MPEG , Matroska, OGM.
MP4 is the global file extension for the official container format defined in the MPEG-4 standard. MP4 is streamable and supports all kinds of multimedia content, multiple audio-, video-, subtitlestreams, pictures, variable-framerates, -bitrates, -samplerates...) and advanced content like 2D and 3D animated graphics, user interactivity, DVD-like menus.
doom9 MP4 FAQ




MPA, MP1, MP2
Shorthand for MPEG Audio elemantary stream(no video). Also called MP2 for MPEG Audio Layer2 but MP2 could also be MPEG2 Audio.




MPEG Audio
MPEG Audio is a family of generic standards for low bit-rate coding
Layer I
low complexity, good for consumer recording
Layer II
high efficiency with medium complexity, good for professional recording and for broadcast
Layer III
high complexity and high efficiency, suitable for very low bit-rates application

key aspects
Input and output signals
AES/EBU
sampling frequencies: 32, 44.1 and 48 kHz
sample representation: PCM max. 24 bits
Coding modes
mono
stereo
joint stereo
dual channel
Bit-rates
from 32 Kbps to:
448 kbps for Layer I
384 kbps for Layer II
320 kbps for Layer III
Coding scheme
masking threshold computation (based on the perceptive model) on a 1152 samples window (384 for Layer I)
signal subdivision in 32 subbands
subband bit allocation according to the masking threshold
Packet structure
Fixed length

MPEG-1: high quality digital audio coding
MPEG1 audio provides:
variable compression factor
different complessity layers
compact disc quality at compression factor ~6
possible use in many applications (broadcasting, telecom, recording, multi-media, etc..)
Compact Disc Quality
The reproduced signal quality must be subjectively indistinguishable from the quality obtained with a 16 bits PCM system sampled at 44.1 kHz (compact disc) in the majority of normal use programs.

MPEG-2: the multi-channel extension
MPEG2 audio extension allows:
compact disc quality
environment sonority reconstruction
sonorous sources location
multilingual transmission
ancillary services
additional freq. 16000Hz, 22050Hz and 24000Hz
MPEG-Multichannel does not only support 5.1 audio, but also 7.1 audio

MPEG-2.5 Audio
additional frequencies added: 8000Hz, 11025Hz and 12000Hz



Layer II multi-channel characteristics
dynamic crosstalk
MPEG-Multichannel does not only support 5.1 audio, but also 7.1 audio

sounds that don't contribute to the source location can be transmitted by any channel

adaptive prediction

an adaptive predictor is used to reduce the inter-channel redundancy
the multi-channel extension channels are predicted from the two base channels
the prediction coefficients can be computed and transmitted at each frame

dynamic channel switching

-----------------------------------------------------------------------------------

the perceptive coding
The studies about the human ear sensitivity to the different frequencies and the different masking effects yielded a perceptive model on which the audio perceptive coding is based.


The static masking
The minimum perceived sonorous pressure, called threshold pressure, depends on several factors, as the source direction, the presence of other sounds, the kind of sound and especially the frequency. To exploit the static masking the threshold pressure must be known for each frequency. It must be noticed that the threshold is subjective and has a statistical value.

The dynamic masking
The dynamic masking is the effect of the threshold pressure increase because of the presence of another sound.
Simultaneous masking
When the masking sound and the masked one occur at the same time. The masking effect depends on the intensity and frequency of both sounds.
Non simultaneous masking
It's possible that the masking sound occurs before (sometimes after) the masked one. Actually the masking effect can last more than the sound by which it's caused.

The noise allocation
Because of all the masking effects the human ear is able to perceive only a part of the sound spectrum. The perceptive model allows the computation of the masking thresold for a defined samples set.
In the perceptive coding the bit-allocation is performed looking at the Signal to Mask Ratio (SMR) obtainable. In such a way bits aren't wasted representing sounds that wouln't be perceived.




Acknowledgments
The help of Giorgio Dimino was essential for providing the information.




MPEG-1
An ISO/IEC (International Organization for Standardization/ International Electrotechnical Commission) standard for medium quality and medium bitrate video and audio compression. It allows video to be compressed by the ratios in the range of 50:1 to 100:1, depending on image sequence type and desired quality. The encoded data rate is targeted at 1.5Mb/s - this was a reasonable transfer rate of a double-speed CD-ROM player (including audio and video). VHS-quality playback is expected from this level of compression. The Motion Picture Expert Group (MPEG) also established the MPEG-2 standard for high-quality video playback at a higher data rates. MPEG-1 is used in encoding video for VCD. MPEG FAQ




MPEG-2
An encoding standard designed as an extension of the MPEG-1 international standard for digital compression of audio and video signals. MPEG-1 was designed to code progressively scanned video at bit rates up to about 1.5 Mbit/s for applications such as CD-i. MPEG-2 is directed at broadcast formats at higher data rates; it provides increased support for efficiently coding interlaced video, supports a wide range of bit rates and provides for multichannel surround sound coding such as PCM, Dolby Digital, DTS and MPEG audio.




MPEG-3
A proposed variant of the MPEG video and audio compression algorithm and file format. MPEG-3 was intended as an extension of MPEG-2 to cater for HDTV but was eventually merged into MPEG-2.

MPEG-3 should not be confused with MP3 which is MPEG-1 layer 3 popularly used for audio encoding.




MPEG-4
An ISO/IEC standard 14496 developed by the Moving Picture Experts Group (MPEG), the committee that also developed MPEG-1 and MPEG-2. These standards made interactive video on CD-ROM, DVD and Digital Television possible. MPEG-4 is the result of another international effort involving hundreds of researchers and engineers from all over the world. MPEG-4 was finalized in October 1998 and became an International Standard in 1999. The fully backward compatible extensions under the title of MPEG-4 Version 2 were frozen at the end of 1999, to acquire the formal International Standard Status early in 2000. Several extensions were added since and work on some specific work-items is still in progress.

MPEG-4 builds on the proven success of three fields:

Digital television
Interactive graphics applications (synthetic content)
Interactive multimedia (World Wide Web, distribution of and access to content)

More information about MPEG-4 can be found at MPEG’s home page




MPEG-7
MPEG-7 is an ISO/IEC standard developed by the Moving Picture Experts Group. MPEG-7, formally named “Multimedia Content Description Interface”, is a standard for describing the multimedia content data that supports some degree of interpretation of the information’s meaning, Unlike previous MPEG standards aimed at encoding, MPEG-7 is not aimed at any one application in particular; rather, the elements that MPEG-7 standardizes support as broad a range of applications as possible. MPEG-7 Alliance




MPEGInfoX
A Mac tool used to give the user various helpful pieces of information about a mpeg file.




mpegproperties
A compact program for Windows PCs that will give you all the parameters for a MPEG file. medialab




MPlayerOSX
One of the more popular VCD/SVCD players for the Mac OS X platform.




MPV, M1V, M2V
MPEG-1 or MPEG-2 video elemantary stream(no audio). Also called M1V for MPEG-1 video and M2V for MPEG-2 video.




MultiAngle, Multi-Angle
A scene recorded from different viewpoints. Each angle is equal in time length and an Angle Block may contain up to nine (9) angles.




Multiplex, Multiplexing, Mux, Muxing
Joining video and audio to one file. Also called "Mux".




Multisystem
Describes a video component that can handle 2 or more types of broadcast video standards. Multisystem televisions, videocassette recorders, and DVD players are not found in all stores but are manufactired by many of the large electronics companies. Why buy multisystem? People who move between countries can play/watch video in both countries. Or if you have a relative in India and want to watch the latest from Bollywood in the US then multisystem works also. Multisystem components often cost more than the single system equivalents. Also some DVD players that are billed as single system VCD capable (NTSC / PAL) can play both.










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