How does mpeg 2 compression work

Default location: Select an item from the pop-up menu to set the default save location for transcoded files. Format: Use the pop-up menu to set the stream type for the output file. There are three options:.

Program streams require an error-free delivery method and are primarily used for storage or processing within a computer. All the channels are multiplexed together, allowing the receiver to choose which to play back. Compressor supports creating single-channel transport streams that can also include associated audio. Transport streams can also recover from interruptions during playback, making them ideally suited for broadcast and streaming applications where noise or network congestion can lead to interruptions.

Compressor modifies the available properties based on the option you choose:. This is the only option that supports the MPEG-2 x video format in addition to the standard-definition SD and high-definition HD video formats.

It supports the complete bit rate range of 2. Blu-ray: This option restricts the encoding properties to those allowed by Blu-ray video discs.

These include the SD and HD video formats and a bit rate range of Add Apple metadata: Select this checkbox to have Compressor parse specific MPEG-2 authoring information during the transcoding process and provide it in the output file.

The resulting file will be read faster by other applications. Include chapter markers only: Select this checkbox to include chapter markers, but not unnamed compression markers, in MPEG-2 output. When this checkbox is deselected, all markers are included in the output file. See Add markers using Compressor. Sets the processing algorithm used to adjust the frame rate during transcoding.

Select one of the following options:. Enter a value in the percentage field or choose a preset value from the adjacent pop-up menu with a down arrow. Set to: Sets the duration of the clip. Enter a timecode duration in the field or click the arrows to increase or decrease the time. So source frames play at [frame rate] fps: Nondestructively changes the playback speed of the clip without discarding frames or creating new frames. For more information, see Retime video and audio using Compressor.

See Intro to supporting captions in Compressor. Frame size: Use this pop-up menu to set the frame size resolution for the output file. There are four categories to choose from:. Pixel aspect ratio: Use this pop-up menu to set the pixel aspect ratio the ratio between the encoded width and the display width.

Frame rate: Use this pop-up menu to set the playback rate the number of images displayed per second for the output file.

See Retiming options in Compressor. Field order: Use the pop-up menu to set the output scanning method either the field dominance or a conversion to progressive scanning. There are four options:.

Automatic: Selects the most appropriate field order, based on the field order of the source and the capabilities of the selected codec. Progressive: The video is displayed in complete frames with all lines sampled at the same instant in time.

Top First: The video is interlaced and displayed as two separate interleaved fields. The field containing the top line even lines is sampled at an earlier instant in time than the field containing the bottom line odd lines.

This field order is commonly used for high-definition video and standard-definition PAL video. Bottom First: The video is interlaced and displayed as two separate interleaved fields. The field containing the bottom line odd lines is sampled at an earlier instant in time than the field containing the top line even lines.

This field order is commonly used for standard-definition NTSC video. Color space: Use this pop-up menu to convert the source media to a new color space. Actions Shares. No notes for slide. Chrominance CbCr : Describes the color of the pixel. For example- A single frame having the resolution of X no.

Thus, for the entire movie, the data would be too big to fit on DVDs or to transmit it using the bandwidth of available TV channels. Top Fields Odd numbered rows in a frame. Spatial redundancy In a frame, adjacent pixels are usually correlated. So the way human eye works, it is also possible to delete some data from the frame with almost no noticeable degradation in image quality. Frame 1 Frame 2 Frame 3 Frame 4 8. P-frame is also a reference frame. Most application uses two consecutive B-frames as the ideal trade off between compression efficiency and video quality.

It takes the advantage of spatial redundancy. Compression techniques are applied using the data of the current frame only. It uses combination of various lossless and lossy compression techniques.

Such as — It takes the advantage of time-based redundancy as well as spatial redundancy. It mainly uses lossy compression techniques. It operates on color space i. A raw frame contains an image in RGB color space.

RGB color space contains mutual redundancies, so it requires large space for storage and high bandwidth for transmission. If an image resolution is x pixels then, the number. Data in frequency domain can be efficiently processed and compressed. Where- Default quantization matrix contains constant values. It is a lossy operation that causes minor degradation in the image quality due to some subtle loss in brightness and colors.

Each component in DCT coefficient matrix is divided by its corresponding constant value in default quantization matrix and a quantized DCT coefficient matrix is computed. A quantization function can be represented as: 16 11 19 16 24 40 51 61 12 12 14 19 26 58 60 55 14 13 16 24 40 57 69 56 14 17 22 29 51 87 80 62 18 22 37 56 68 77 24 35 55 64 81 92 49 64 78 87 72 92 95 98 99 Default Quantization Matrix That is, the above sequence can be represented as 12W1B12W3B.

EOB to end the sequence prematurely when the remaining coefficients are zero and then it performs variable length encoding for further compression. Bit rate control is necessary in applications that requires fixed bit rate transmission of encoded bit-stream. Using forward interpolated prediction , encoder can forward predict a future frame called P-frame. The very first P-frame in a group of picture , is predicted from the I-frame immediately preceding it. Other P-frame in a group of picture can be predicted from previous I-frame or P-frame immediately preceding it.

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An excellent example is the transmission of television pictures. Taking these techniques in order: Motion vector estimation is used to capture much of the change between video frames, in the form of best approximations of each part of a frame as a translation generally due to motion of a similar-sized piece of another video frame.

What happens when MPEG-2 breaks? However, the best laid plans sometimes fail; the following are some of the more common MPEG-2 artifacts: If the compression ratio is too high, there are sometimes simply not enough bits to encode the video signal without significant loss. Overview Pearson Education, Inc. Collection and Use of Information To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including: Questions and Inquiries For inquiries and questions, we collect the inquiry or question, together with name, contact details email address, phone number and mailing address and any other additional information voluntarily submitted to us through a Contact Us form or an email.

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