Mpeg Info

Request information about the ATSC 3.0 patent submission and license facilitation process from MPEG LA. MPEG LA is the world's leading packager and provider of one-stop licenses for standards and other technology platforms. We developed the pool market space. Our 'many-to-many licensing model' has revolutionized the way patent holders, developers and users think about the intellectual property market creating reasonable access and profitable opportunities for everyone.

Oct 16, 2020 • Filed to: Photo/Video/Audio Solutions • Proven solutions

Digital video coding has come a long way from when the idea was introduced in 1967 with H. 120 as the first digital coding standard. The MPEG2 was introduced in 1994, the MPEG4 in 1999, and the H.264 in 2003.

This article will enumerate the features of MPEG2, MPEG4, and H264, as well as explain their differences.

Part 1: What is H 264 Video Format?

The H. 264 video coding format, which is also known as the H.264/MPEG-4 AVC (Advanced Video Coding) is the most widely used format for the recording, compression, and distribution of video content as of September of this year. If you've used internet streaming sources like Netflix and YouTube and web software like the Adobe Flash Player, then you've seen the H.264 at work. Various HDTV broadcasts over terrestrial, cable, and satellite also make use of the H.264 video coding format.

It was standardized by the ITU-T Video Coding Experts Group (VCEG) together with the ISO/IEC JTC1 Moving Picture Experts Group (MPEG). The first version was completed in 2003. The H.264 video format intended to provide good video quality at a bit rate lower than the video coding formats that came before it. It was meant to do this without increasing the complexity of the design or becoming too expensive to implement. It was also meant to be flexible so that it could be applied to a wide variety of networks and systems.

The H.264 achieved all of the above successfully by using features such as:

• The variable block-size segmentation
• A reduced-complexity integer transform
• Multi-picture inter-picture prediction.

Also, its top advantages include the following:

• H.264 supports resolutions up to and including 8K UHD
• It is best known for being the most commonly used video encoding format on Blu-ray discs.
• When it comes to video network and High Definition (HD) videos, H.264 provides a highly attractive delivery.
• The H.264 has undergone a lot of updates starting from version 2 which was released in 2004 with various minor corrections. It is currently on its 26th version which was released in June 2019 and had amendments to the content light level information, region-wise packing, content color volume, sphere rotation, and lots more.

Part 2: What is MPEG2 and MPEG4?

The Moving Pictures Experts Group (MPEG) is the body responsible for the standards used in video encoding, standards like MPEG2 and MPEG4. This section will give you the information you need on the MPEG2 and MPEG4.

1. What is MPEG2?

MPEG2 is the codec used to compress digital broadcast video and DVDs. Media files encoded with the MPEG-2 codec usually have the file extensions .mpg, .mpeg, .m2v, .mp2, or in some cases, .mp3. It is also known as H.262 and is still used in over-the-air digital television broadcasting and the DVD-Video standard.

The MPEG2 was created in 1994 to fix the shortcomings of its predecessor MPEG1. It is still in use because of a need for backward compatibility with existing hardware and software. It was developed primarily by Sony, Thomson, and Mitsubishi Electric. After its release, it became the standard video format for DVD and SD digital television.

The advantages you will enjoy when using the MPEG2 format include:

• A video quality that is superior to those of other video formats
• A very simple method of video compression
• An ability to handle video streams from such local sources as cable broadcasts and DVDs.

2. What is MPEG4?

The MPEG4 standard is an MPEG4 format that was initiated in 1995. It reached a committee draft status in 1998 (March) and at the end of the same 1998, its creation was finalized. Initially, it was created specifically for bit rates that were very low but presently, it can support up to 4Mbps. MPEG4 contains six parts which make it able to perform its functions, they are visual, software, systems, Delivery Multimedia Integration Framework (DMIF), conformance testing, and audio.

This video encoding standard is designed to be used in broadcast, in conversational, and interactive environments. It is also designed to carry out content-based scalability. Because of how MPEG4 is built (having adopted features from MPEG1, MPEG2, and VRML), you can use it in both web environments and television and you can integrate content from both channels into the same multimedia environment.

The advantages of MPEG4 can be seen in more of its features and these include:

• An integration of both synthetic and natural content in object form. An object could be a representation of recorded entities like a chair, a person; or synthesized material like a face, a person, an animated 3D model.
• Great support for content in 2D, as well in 3D
• Support for all kinds of interactivity
• It can code efficiently from very low rates (5 Kbit/s for videos and 2 Kbit/s for speech) to very high rates (up to 64 Kbit/s per channel for quality Audio of CDs and 5 Mbit/a for transparent quality Video)
• With the use of URLs, it adds to VRML native support for contents that are natural and streamed in real-time.
• A scene description that is efficiently represented.
• A wide range coverage of bit rates, qualities, and services, applications, and resolutions.

Also, this format supports compatibility with the other standards that are already in existence, such as MPEG1, MPEG2, VRML, H.263, and ITU-T. Its impact is felt in two areas:

1. In production, programming, and archiving. Here, it allows broadcasters to browse with ease and speed, video archives.

2. In repurposing assets of digital video. MPEG-4 is what broadcasters need when it comes to the distribution of content over IP, broadband, and mobile networks, and not just through a traditional broadcast system. MPEG4 has a high efficiency when it comes to coding for low bit rates which makes it ideal for the job.

3. Are MP4 and MPEG4 the same thing?

Many people tend to confuse MP4 and MPEG4 by assuming both are the same thing or variations of the same thing. This is not the case as each means a different thing. Simply put, MP4 is a store or container format while MPEG4 is a video encoding standard or format.

• MPEG4 is a standard for video encoding. It is used for the compression of AV data for distribution over the web and in CDs; for voice sound (videophone and telephone), and also for television broadcast.
• MP4 was developed from Apple's MOV file to store video files that have been encoded by MPEG4. Note that MP4 can also store digital data (video and audio) that has been encoded by other encoding formats.
• Similarly, both MPEG4 and MP4 are software developed by the Moving Picture Experts Group (MPEG). MP4 is one of the latest video formats developed for efficient video distribution and streaming through the internet while MPEG4 has been developed since the '90s as a standard for encoding videos.

Part 3: MPEG2 VS MPEG4 VS H264

1. Differences among MPEG2, MPEG4, and H264:

To give you a better understanding of the MPEG2, MPEG4, and H264 standards, their features are compared below:

• The MPEG4 format uses an algorithm that has a 16 x 16 DCT (Discrete Cosine Transform); this allows for a higher rate of compression. This is a notable difference between MPEG2 and MPEG4.
• Both MPEG4 and MPEG2 provide high-definition video quality, which is higher than H264. However, MPEG2 produces the best when it comes to video quality.
• MPEG2 has a larger file size than MPEG4 and H264 which makes it difficult to be compatible with portable devices, along with internet video streaming. On the other hand, MPEG4 with its high rate of compression in smaller file sizes can work across mobile networks without losing its high-quality.
• If you want to encode your digital data on DVDs, the ideal method to use is MPEG2. If you want to encode your digital data online and in portable devices, MPEG4 is the go-to encoding standard. For video encoding on Blu-ray discs, the H264 is recommended as the most commonly used format.
• Compared to MPEG4, the MPEG2 format is quite easier to use as a video compression format. However, H264 is open and it has a published specification, available for implementation by basically anyone.
• MPEG4 contains more interactive features that allow you to manipulate different elements on your videos in real-time.
• H264 has the most flexibility which allows it to be applied to many different applications on a wide range of systems and networks.

2. How to Make a Video Format Conversion:

Video formats are usually converted from one form to another for various reasons such as compatibility with the user's device, higher quality. There are many video converters you can use to convert videos from one format to another. Choose the converter you prefer and follow these standard steps to convert one form of video format to another:

• Select the video files you wish to convert
• Choose the output format i.e, the video format you want to convert your video to
• Click on the 'Convert' button or option to begin the conversion process
• Save the converted video file to your desired location by clicking on the 'Download' option.

Part 4: How to Recover and Repair Videos

Videos get corrupt or missing many times due to one factor or the other. This has made it necessary to know how to repair videos when they get damaged and recover them when they get missing from your computer. In this part, you will learn why videos get missing and corrupt. You will be shown the best tool to use for recovering videos that are missing from your system storage. More importantly, you will know the tool to use for repairing videos that are corrupt on your system and how to use it.

There is a need for you to repair your videos if they get damaged or corrupted from the following:

• Error: An error can occur from shooting a video, playing it back, or during the transfer from one device to another. An error can also come from the system itself if it is corrupt.
• Virus infestation or malware infection: Any system affected with viruses tends to corrupt all the files stored within it; this includes your saved video files.

If your video gets corrupted for any reason, you can use the Recoverit Video Repair tool to perform a quick or advanced repair of your videos. All you need to do is use the following steps as a guide:

Step 1: Add the corrupt video file.

Use the 'Drag and drop' option to move your corrupted video files to the Recoverit Video Repair interface.

Step 2: Start the process of video repair.

Select 'Repair' to start repairing the video files you have added.

Step 3: Preview and save videos.

The progress bar will display the repair process so you can be aware of when it is complete. Preview the repaired video file before saving it to a location of your choice.

Step 4: Proceed to Perform 'Advance Repair'.

For an advanced repair, a sample video is shot by Recoverit. The sample video is in the same format as your corrupt video file, and it is created from the same device. Therefore, Recoverit uses the information in the sample video as a reference in repairing your severely damaged video.

Step 5: Add sample video files.

For an effective advanced video recovery, ensure you add the sample video files, and repair the corrupt video once again. Next, save the files.

This article has been able to explain the meanings of MPEG2, MPEG4, and, H264. In light of this, these video compression formats have been compared and their differences are clearly defined. You can now make an informed decision on what format to use for your video compression, based on their peculiarities.

Solve All Media File Issues

Recover & Repair Photos

Recover & Repair Videos

Recover & Repair Audio

Recover & Repair Cameras

What is MPEG?

MPEG stands for 'Moving Pictures Experts Groups'. It is a group working underthe directives of the International Standards Organisation (ISO) and theInternational Electro-Technical Commission (IEC).

Vault 101 1 3 download free. The groups work concentrates on defining standards for the coding of movingpictures, audio and related data.

MPEG-1 defines a framework for coding moving video and audio, significantlyreducing the amount of storage with minimal perceived difference in quality. Inaddition a System specification defines how audio and video streams can becombined to produce a system stream. This forms the basis of the coding used forthe VCD format.

MPEG-2 builds on the MPEG-1 specification, adding further pixel resolutions,support for interlace picture, better error recovery possibilities, morechrominance information formats, non-linear macroblock quantization and thepossibility of higher resolution DC components.

MPEG video compression

MPEG video compression uses several techniques to achieve high compressionratios with minimal impact on the perceived video quality.

Mpeg Info Free

Discrete Cosine Transformation (DCT)

The human vision system exhibits some characteristics that are exploited byMPEG video compression. One of these is that large objects are much morenoticeable than detail within them. In other words, low spatial frequencyinformation is much more noticeable than high spatial frequency information.

MPEG video compression discards some high spatial frequency information - theinformation which is less noticeable to the eye. The first step in this process isto convert a static picture into the frequency domain. The DCT performs thistransformation.

A complete frame is split into blocks of 8x8 pixels. The DCT algorithmconverts the spatial information within the block into the frequency domain.After the transformation, the top left value of the block represents the DClevel (think of this as the average brightness) of the block. The valueimmediately to the right of this represents low frequency horizontalinformation. The value in the top right represents high frequency horizontalinformation. Similarly, the bottom left value represents high frequency verticalinformation.

The following diagrams show a 4x4 block of pixels and the resulting DCTvalues. Values in the DCT output matrices range from 0 to 15.

The Moving Pictures Experts Group (MPEG) is the body responsible for the standards used in video encoding, standards like MPEG2 and MPEG4. This section will give you the information you need on the MPEG2 and MPEG4.

1. What is MPEG2?

MPEG2 is the codec used to compress digital broadcast video and DVDs. Media files encoded with the MPEG-2 codec usually have the file extensions .mpg, .mpeg, .m2v, .mp2, or in some cases, .mp3. It is also known as H.262 and is still used in over-the-air digital television broadcasting and the DVD-Video standard.

The MPEG2 was created in 1994 to fix the shortcomings of its predecessor MPEG1. It is still in use because of a need for backward compatibility with existing hardware and software. It was developed primarily by Sony, Thomson, and Mitsubishi Electric. After its release, it became the standard video format for DVD and SD digital television.

The advantages you will enjoy when using the MPEG2 format include:

• A video quality that is superior to those of other video formats
• A very simple method of video compression
• An ability to handle video streams from such local sources as cable broadcasts and DVDs.

2. What is MPEG4?

The MPEG4 standard is an MPEG4 format that was initiated in 1995. It reached a committee draft status in 1998 (March) and at the end of the same 1998, its creation was finalized. Initially, it was created specifically for bit rates that were very low but presently, it can support up to 4Mbps. MPEG4 contains six parts which make it able to perform its functions, they are visual, software, systems, Delivery Multimedia Integration Framework (DMIF), conformance testing, and audio.

This video encoding standard is designed to be used in broadcast, in conversational, and interactive environments. It is also designed to carry out content-based scalability. Because of how MPEG4 is built (having adopted features from MPEG1, MPEG2, and VRML), you can use it in both web environments and television and you can integrate content from both channels into the same multimedia environment.

The advantages of MPEG4 can be seen in more of its features and these include:

• An integration of both synthetic and natural content in object form. An object could be a representation of recorded entities like a chair, a person; or synthesized material like a face, a person, an animated 3D model.
• Great support for content in 2D, as well in 3D
• Support for all kinds of interactivity
• It can code efficiently from very low rates (5 Kbit/s for videos and 2 Kbit/s for speech) to very high rates (up to 64 Kbit/s per channel for quality Audio of CDs and 5 Mbit/a for transparent quality Video)
• With the use of URLs, it adds to VRML native support for contents that are natural and streamed in real-time.
• A scene description that is efficiently represented.
• A wide range coverage of bit rates, qualities, and services, applications, and resolutions.

Also, this format supports compatibility with the other standards that are already in existence, such as MPEG1, MPEG2, VRML, H.263, and ITU-T. Its impact is felt in two areas:

1. In production, programming, and archiving. Here, it allows broadcasters to browse with ease and speed, video archives.

2. In repurposing assets of digital video. MPEG-4 is what broadcasters need when it comes to the distribution of content over IP, broadband, and mobile networks, and not just through a traditional broadcast system. MPEG4 has a high efficiency when it comes to coding for low bit rates which makes it ideal for the job.

3. Are MP4 and MPEG4 the same thing?

Many people tend to confuse MP4 and MPEG4 by assuming both are the same thing or variations of the same thing. This is not the case as each means a different thing. Simply put, MP4 is a store or container format while MPEG4 is a video encoding standard or format.

• MPEG4 is a standard for video encoding. It is used for the compression of AV data for distribution over the web and in CDs; for voice sound (videophone and telephone), and also for television broadcast.
• MP4 was developed from Apple's MOV file to store video files that have been encoded by MPEG4. Note that MP4 can also store digital data (video and audio) that has been encoded by other encoding formats.
• Similarly, both MPEG4 and MP4 are software developed by the Moving Picture Experts Group (MPEG). MP4 is one of the latest video formats developed for efficient video distribution and streaming through the internet while MPEG4 has been developed since the '90s as a standard for encoding videos.

Part 3: MPEG2 VS MPEG4 VS H264

1. Differences among MPEG2, MPEG4, and H264:

To give you a better understanding of the MPEG2, MPEG4, and H264 standards, their features are compared below:

• The MPEG4 format uses an algorithm that has a 16 x 16 DCT (Discrete Cosine Transform); this allows for a higher rate of compression. This is a notable difference between MPEG2 and MPEG4.
• Both MPEG4 and MPEG2 provide high-definition video quality, which is higher than H264. However, MPEG2 produces the best when it comes to video quality.
• MPEG2 has a larger file size than MPEG4 and H264 which makes it difficult to be compatible with portable devices, along with internet video streaming. On the other hand, MPEG4 with its high rate of compression in smaller file sizes can work across mobile networks without losing its high-quality.
• If you want to encode your digital data on DVDs, the ideal method to use is MPEG2. If you want to encode your digital data online and in portable devices, MPEG4 is the go-to encoding standard. For video encoding on Blu-ray discs, the H264 is recommended as the most commonly used format.
• Compared to MPEG4, the MPEG2 format is quite easier to use as a video compression format. However, H264 is open and it has a published specification, available for implementation by basically anyone.
• MPEG4 contains more interactive features that allow you to manipulate different elements on your videos in real-time.
• H264 has the most flexibility which allows it to be applied to many different applications on a wide range of systems and networks.

2. How to Make a Video Format Conversion:

Video formats are usually converted from one form to another for various reasons such as compatibility with the user's device, higher quality. There are many video converters you can use to convert videos from one format to another. Choose the converter you prefer and follow these standard steps to convert one form of video format to another:

• Select the video files you wish to convert
• Choose the output format i.e, the video format you want to convert your video to
• Click on the 'Convert' button or option to begin the conversion process
• Save the converted video file to your desired location by clicking on the 'Download' option.

Part 4: How to Recover and Repair Videos

Videos get corrupt or missing many times due to one factor or the other. This has made it necessary to know how to repair videos when they get damaged and recover them when they get missing from your computer. In this part, you will learn why videos get missing and corrupt. You will be shown the best tool to use for recovering videos that are missing from your system storage. More importantly, you will know the tool to use for repairing videos that are corrupt on your system and how to use it.

There is a need for you to repair your videos if they get damaged or corrupted from the following:

• Error: An error can occur from shooting a video, playing it back, or during the transfer from one device to another. An error can also come from the system itself if it is corrupt.
• Virus infestation or malware infection: Any system affected with viruses tends to corrupt all the files stored within it; this includes your saved video files.

If your video gets corrupted for any reason, you can use the Recoverit Video Repair tool to perform a quick or advanced repair of your videos. All you need to do is use the following steps as a guide:

Step 1: Add the corrupt video file.

Use the 'Drag and drop' option to move your corrupted video files to the Recoverit Video Repair interface.

Step 2: Start the process of video repair.

Select 'Repair' to start repairing the video files you have added.

Step 3: Preview and save videos.

The progress bar will display the repair process so you can be aware of when it is complete. Preview the repaired video file before saving it to a location of your choice.

Step 4: Proceed to Perform 'Advance Repair'.

For an advanced repair, a sample video is shot by Recoverit. The sample video is in the same format as your corrupt video file, and it is created from the same device. Therefore, Recoverit uses the information in the sample video as a reference in repairing your severely damaged video.

Step 5: Add sample video files.

For an effective advanced video recovery, ensure you add the sample video files, and repair the corrupt video once again. Next, save the files.

This article has been able to explain the meanings of MPEG2, MPEG4, and, H264. In light of this, these video compression formats have been compared and their differences are clearly defined. You can now make an informed decision on what format to use for your video compression, based on their peculiarities.

Solve All Media File Issues

Recover & Repair Photos

Recover & Repair Videos

Recover & Repair Audio

Recover & Repair Cameras

What is MPEG?

MPEG stands for 'Moving Pictures Experts Groups'. It is a group working underthe directives of the International Standards Organisation (ISO) and theInternational Electro-Technical Commission (IEC).

Vault 101 1 3 download free. The groups work concentrates on defining standards for the coding of movingpictures, audio and related data.

MPEG-1 defines a framework for coding moving video and audio, significantlyreducing the amount of storage with minimal perceived difference in quality. Inaddition a System specification defines how audio and video streams can becombined to produce a system stream. This forms the basis of the coding used forthe VCD format.

MPEG-2 builds on the MPEG-1 specification, adding further pixel resolutions,support for interlace picture, better error recovery possibilities, morechrominance information formats, non-linear macroblock quantization and thepossibility of higher resolution DC components.

MPEG video compression

MPEG video compression uses several techniques to achieve high compressionratios with minimal impact on the perceived video quality.

Mpeg Info Free

Discrete Cosine Transformation (DCT)

The human vision system exhibits some characteristics that are exploited byMPEG video compression. One of these is that large objects are much morenoticeable than detail within them. In other words, low spatial frequencyinformation is much more noticeable than high spatial frequency information.

MPEG video compression discards some high spatial frequency information - theinformation which is less noticeable to the eye. The first step in this process isto convert a static picture into the frequency domain. The DCT performs thistransformation.

A complete frame is split into blocks of 8x8 pixels. The DCT algorithmconverts the spatial information within the block into the frequency domain.After the transformation, the top left value of the block represents the DClevel (think of this as the average brightness) of the block. The valueimmediately to the right of this represents low frequency horizontalinformation. The value in the top right represents high frequency horizontalinformation. Similarly, the bottom left value represents high frequency verticalinformation.

The following diagrams show a 4x4 block of pixels and the resulting DCTvalues. Values in the DCT output matrices range from 0 to 15.

Our DCT transformed values contain an accurate representation of our originalmacroblock. By applying an inverse DCT on the values we regain our originalpixels. Our DCT output is currently held as high precision (e.g. floating point)values. We apply a technique called quantization to reduce the precisionof the values. Quantization simply means storing the value using a discretenumber of bits, discarding the least significant information. By using theknowledge that the high spatial frequency information is less visible to the eyethan low frequency we can quantize the high frequency parts using fewer bits. Itis important that the DC component is accurately represented.

In our example blocks above, we have used 4 bit (values in the range 0 to 15)values to represent the DCT matrix. Itrash 4 0 0 download free. With the knowledge that the eye cannotdetermine high frequency information as accurately as low frequency information,we can change the number of bits that we quantize each entry in the matrix. TheDC component must be accurately represented, but we can reduce the number ofbits required for other cells. The following shows an example of how many bitscould be allocated for each call in the DCT matrix:

The original matrix had 16 cells with 4 bits per cell, giving a total of 64bits. The quantized matrix has a total of:

A saving of about 50%. A real MPEG encoder varies the number of bits that DCTmatrix vales are coded to on each frame.

Modified Huffman Coding

Modified Huffman coding uses fixed tables to perform Huffman coding. The DCToutput is encoded using this technique to reduce the number of bits required.The basis of Huffman encoding is that encoded symbols are a variable number ofbits. Frequently used symbols consume fewer bits, less frequently used symbolsconsume more bits. The result is a (hopefully!) saving in the bit requirements.

Encoding Motion

MPEG video frames are broken into blocks of 8x8 pixels which are DCTprocessed and quantized as outlined above. Blocks are combined into macroblocks of 16x16 or 16x8 (MPEG-2 only) pixels.

Lets consider a sequence of 6 frames. The encoder starts by encoding acomplete representation of the first frame (similar to a static JPEG image).This is known as an Intra-Frame (or I-Frame). I-frames are necessary to give thedecoder a starting point.

The encoder could choose to encode the fourth frame in the video as aPredicted frame (or P-frame). To do this is scans the first frame (the reference frame) and the fourth frame, looking for macroblock size areas ofthe picture that appear similar. If the video contains moving objects, theencoder detects this. For areas of the image which have not changed betweenfirst and fourth frame, macroblocks are skipped. Skipped macroblocks do notconsume any data in the video stream. The decoder simply copies the macroblockfrom the previous reference frame. For areas that have changed slightly comparedto the reference it takes the pixel difference and encodes this using DCT andquantization techniques. For areas that the encoder can detect the movement ofan object from one macroblock position to another it encodes a motion vector and difference information. The motion vector tells the decoder how far andin what direction the macroblock has moved. Where the encoder cannot find asimilar macroblock in the reference frame, the macroblock is encoded as if itwas an I-frame.

The other frames in the sequence (second, third, fifth and sixth) could beencoded as Bidirectional Predicted frames (B-frames). Considering the secondframe, this has two reference frame; the previous reference frame isframe one and the next reference frame is frame four. A B-frame can usemacroblocks from either the previous or next reference frames, or preferably acombination of both. Using forward and backward motion vectors allowsinterpolation of 2 images, reducing noise at low bitrates.

Using our example, video would be encoded using the frame sequence:

It is more normal for I frames to appear less regularly than this, perhapsevery 12 frames. A more sophisticated encoder would dynamically detect whichframes should be encoded using which frame types, e.g. a scene change wouldresult in an I frame being inserted. Thus the sequence could end up looking morerandom, such as:

By using information from previous and next pictures, substantial saving canbe made in the bit requirements for P and B pictures compared with I pictures.Typically P-frames would require 30% to 50% the number of bits compared to I-frames,B-frames would require 15% to 25% the number of bits.

Que Es Mpeg Informatica

MPEG audio compression

Audio data is sampled at a certain sample rate. That means that anumber of measurements of the audio signal are taken every second (32,000,44,100 or 48,000 samples per second for MPEG-1 audio). Each sample is taken ata certain precision (16 bits).

MPEG audio compression uses a psycho-acoustic model of the human ear todetermine portions of the audio information that can be encoded at a lowerprecision without impacting the listeners perception.

The first step in encoding MPEG audio is to use our old friend, the discretecosine transform (DCT) to convert a short burst of audio data (known as a frame) into the frequency domain. The DCT converts from time samples into 32equally spaced frequency bands. Using the psycho-acoustic model, the number ofdata bits used to represent the sampled data can be varied for differentfrequency bands. Audio information that will not be heard is not allocated anybits.

Frequency (Auditory) Masking

Frequency masking or auditory masking is a term used todescribe masking of a sound at one frequency by a sound at another frequency. Ifa loud sound is present at a particular frequency it reduces the ability of thehuman ear to discern a softer sound at a second frequency. The louder the firstfrequency is and the closer the two frequencies the greater the effect.

To illustrate, if a -6db signal is present at 1kHz (1000 Hz) and anothersignal present at 1.1kHz (1100 Hz) with a loudness of -18dB, the 1.1kHz signalwill not be heard.

Temporal Masking

Temporal masking is the masking of a sound by another sound thatoccurred before or after it in time. If a loud sound stops abruptly and isreplaced by a soft (low volume) sound of short duration, the soft sound will notbe heard until the ear can recover from the effects of the loud sound.

A similar effect in the other direction is also possible where a soft soundof short duration is followed by a loud sound. Once again the soft sound is notheard.