MPEG-1

According to abbreviationfinder, MPEG-1 is the name of a group of Audio and Video coding standards standardized by the MPEG group (Moving Pictures Experts Group). It is used in the Video CD format. The output quality with the usual compression rate used in VCD is similar to that of a home VHS video cassette. For audio, the MPEG group defined MPEG-1 audio layer 3 better known as MP3.

Concept

MPEG -1: is the initial standard for video and audio compression. Provides video with a resolution of 352×240 at 30 frames per second (fps). This produces a video quality slightly lower than the quality of conventional VCR videos. Includes Layer 3 (MP3) audio compression format.

Reproduction

To play a video on a tabletop DVD player or portable device, the video must be converted to one of the standardized MPEG formats.

There are several MPEG formats and not all of them may be compatible with your device. To check the formats supported by the drives, it is necessary to review the documentation of the device carefully.

MPG is basically a container format, since it can contain several audio and video tracks, or even optional subtitle tracks. Depending on the properties of the audio and video (resolution, bitrate, FPS, etc.), the MPG file will conform to a certain standard.

Qualities

The MPEG-1 standard represents each image as a set of 16 X 16 blocks. It allows obtaining a resolution of:

• 352 x 240 @ 30 images per second in NTSC
• 352 x 288 at 25 images per second in PAL / SECAM

MPEG-1 allows speeds of around 1.2 Mbps (which can be read on a CD-ROM).

MPEG-1 allows you to encode videos through several techniques:

• Intracoded frames (I frames, corresponding to an internal encoding): the images are encoded separately without referring to the preceding images
• Predictive code frames (P frames or predictive coding) – Images are described by their differences from preceding images
• Bidirectional predictive code frames (B frames): images are described by their differences from the preceding image and from the next image
• Coded DC frames: images are coded by averaging the blocks

Parts that make it up

MPEG-1 is made up of different parts:

• Synchronization and simultaneous transmission of video and audio.
• Compression codec for non- interlaced (progressive) video signals.
• Compression codec for audio signals with control over the compression rate. The standard defines three layers, or levels of complexity, of MPEG audio encoding.
• MP1 or MPEG-1 Part 3 Layer 1 (MPEG-1 Audio Layer 1)
• MP2 or MPEG-1 Part 3 Layer 2 (MPEG-1 Audio Layer 2)
• MP3 or MPEG-1 Part 3 Layer 3 (MPEG-1 Audio Layer 3)
• Procedures to verify conformity.
• Reference software.

MPEG-2

MPEG-2. It is used in the broadcasting of digital video and digital versatile discs. The Transport Stream (TS) and Program Stream (PS) are digital formats containers.

MPEG | M oving P ictures E xperts G roup 2 (MPEG-2), is the designation for a group of audio and video coding standards agreed by MPEG(group of experts in moving images), and published as ISO 13818 standard. MPEG -2 is generally used to encode audio and video for broadcast signals, including digital terrestrial, satellite, or cable television. MPEG-2. With some modifications, it is also the encoding format used by commercial SVCD and DVD movie discs.

MPEG-2 is similar to MPEG-1, but it also provides support for interlaced video (the format used by televisions.) MPEG-2 video is not optimized for low bit rates (less than 1 Mbit / s), but exceeds in performance to MPEG-1 at 3 Mbit / s and higher.

Emergence

MPEG2, used by digital television and DVD. MPEG2 appeared in 1994 and is one of the compression formats that offers the highest image quality, in turn reaching a data transmission speed of 3 to 10 Mbits of bandwidth. This format offers the transmission of full-screen or broadcast digital video files.

Concept

The MPEG-2 standard (Group of Experts in Image Movement) falls within the standards of audio and video coding. All this is already published in the ISO 13818 quality standard, which includes, for example, broadcasting by DTT, satellite or cable and is also used by the SVCD and DVD discs so classic in homes.

Main features in video encoding for MPEG-2

• Supports interlace video.
• Improvement in quality to MPEG-1 with a bit rate> 3Mb / s.
• It introduces Transport Streams capable of transmitting audio and video in very difficult conditions, for example in television productions.
• The current HDTV (High Definition Television) format complies with the MPEG-2 standard and with a decoder it will also play MPEG-1.

MPEG-2 introduces and defines Transport Streams, which are designed to transport digital video and audio through unpredictable and unstable media, and are used in television broadcasts. With some improvements, MPEG-2 is also the current standard for HDTV broadcasts. A decoder that complies with the MPEG-2 standard must be capable of playing MPEG-1.

MPEG-2 audio, defined in Part 3 of the standard, improves on MPEG-1 audio by accommodating the encoding of audio programs with more than two channels. Part 3 of the standard allows it to be made backwards compatible, allowing MPEG-1 audio decoders to decode the Stereocomponent of the two master channels, or in a non-backwards compatible way, which allows encoders to make better use of it. available bandwidth. MPEG-2 supports various audio formats, including MPEG-2 AAC.

The MPEG-2 standard

General information about MPEG-2 Video and MPEG-2 Audio excluding modifications when used in DVD / DVB.

A typical MPEG-2 System Stream consists of two elements:

video data + time stamps audio data + time stamps

MPEG-2 video encoding (simplified)

MPEG-2 is for generic encoding of moving pictures and associated audio that creates a video stream using three types of frame data (intra frames, predictable back frames, and bi-directional predictable frames) arranged in a specific order called ” The GOP structure ”(GOP = Group Of Pictures or group of images).

Generally the source material is a video sequence at a pixel resolution preset at 25 or 29.97 frames per second with sound.

MPEG-2 supports both progressive and interlaced scanned video streams. In progressive scan streams, the basic encoding unit is a field. In the discussion below, the generic terms “box” and “image” refer to both fields or boxes, depending on the type of flow.

The MPEG-2 stream is made up of a series of encoded picture frames. The three ways to encode an image are: intra-coded (I frame), posterior predictable (P frame) and bi-directional predictable (B frame).

The video image is separated into two parts: luminance (Y) and chroma (also called U and V color difference signals) in turn, they are divided into “Macro-blocks” which are the basic unit within an image.. Each macro-block is divided into four 8X8 luminance blocks. the number of 8X8 chroma blocks depends on the font color format. For example in the common 4: 2: 0 format there is one chroma block per macro-block for each channel making a total of six blocks per macro-block.

In the case of I frames, the true image information passed through the encoding process described below, the P and B frames are first subjected to a “motion compensation” process, in which they are co-related to the image. previous (and in the case of table B, the following).

Each macro-block in image P or B is then associated with an area in the previous or next image that is well correlated with any of these. The “motion vector” that maps the macro-block to its correlated area is encoded, and then the difference between the two areas is passed through the encoding process described below.

Each block is processed with an 8X8 discrete cosine transform (DCT). The resulting DCT coefficient is then quantized according to a predefined scheme, rearranged to a maximum probability from a long string of zeros, and encoded. Finally, a fixed table Huffman encoding algorithm is applied.

The I frames encode spatial redundancy, while the B and P frames encode temporal redundancy. Because adjacent frames are often well co-related, P frames can be 10% the size of an I frame, and B frame 2% of its size.

The sequence of different types of frames is called the “group picture structure” (GOP). There are many possible structures, but a common one is 15 frames long, and it has the sequence I_BB_P_BB_P_BB_P_BB_P_BB_. A similar 12-frame sequence is also common. The I, P and B frame ratio in “the GOP structure is determined by the nature of the video stream and the bandwidth constraining the stream, and encoding time can be an important issue.

This is particularly true in live broadcasts and in real-time environments with limited compute sources, a stream containing several B-frames can take three times longer to encode than a file containing only I-frames.

The output bit rate of an MPEG-2 encoder can be constant (CBR) or variable (VBR), with a maximum determined by the player – for example the maximum possible on a movie DVD is 10.4 Mbit / s. To achieve a constant bit rate the degree of quantization is altered to achieve the required bit rate.

Increasing the quantization makes a flaw visible when the video is decoded. Generally in the form of “amosaicamiento”, where the discontinuities in the edges of the macro-blocks become more visible as a reduction of the bit rate.

MPEG-2 audio encoding.

MPEG-2 also introduces new audio encoding methods. These are:

• Low encoding bitrate with split sampling rates (MPEG-1 layer 1/2/3 LSF)
• Multi-channel encoding up to 6 channels (5.1)

MPEG-2 On SVCD

Additional restrictions and modifications of MPEG-2 on SVCD:

• Resolution
  • 480 x 480 pixels NTSC (USA, Japan)
  • 480 x 576 pixels PAL (Europe)
• Aspect ratio
  • 4: 3
• Frame rate
  • 94 fields / s, 29.97 frames / s (NTSC)
  • 50 fields / s, 25 frames / s (PAL))
• Audio + video bit rate
  • Peak 2.52 Mbit / s
  • Minimum 300 Kbit / s
  • YUV 4: 2: 0
• Audio
  • MPEG-1 layer 2 (MP2): 44.1KHz, 224 Kbit / s, Stereo
• GOP structure
  • Header sequence should be output for each GOP
  • There is no maximum GOP limit

MPEG-2 On DVD

Additional restrictions and modifications of MPEG-2 on DVD:

Video Resolution:

• NTSC (USA, Japan) Pixels
  • 720 x 480
  • 704 x 480
  • 352 x 480
  • 352 x 240
• PAL (Europe) Pixels
  • 720 x 576
  • 704 x 576
  • 352 x 576
  • 352 x 288
• Aspect ratio
  • 4: 3
  • 16: 9
• Frame rate
  • 94 fields / s
  • 50 fields / s
  • 23,976 frames / s (with 3: 2 flags)
  • 97 frames / s (NTSC)
  • 25 frames / s (PAL)
• Audio:
  • Linear Pulse Code Modulation: 48KHz or 96KHz, 16 bit, 2 channels (Stereo)
  • MPEG-1 Layer 2 (MP2): 48KHz, up to 7.1 channels (required in PAL players)
  • Dolby Digital (DD): 48KHz, 448 kbit / s, up to 5.1 channels
  • Digital Theater Systems: 754 kbit / s or 1510 kbit / s (not required to comply with the player)
  • There must be at least one non-DTS audio track (or MP2 for NTSC)
• Audio + video bit rate:
  • 8 Mbit / s average maximum buffer
  • Peak 15 Mbit / s
  • Minimum 300 Kbit / s
  • YUV 4: 2: 0
• Optional subtitles possible
  • Closed captioning (NTSC only)
• GOP structure
  • Header sequence should be output for each GOP
  • 18 frames max per GOP
  • Closed GOP required for multi-angle DVD

MPEG-2 in DVB

Additional restrictions and modifications for DVB-MPEG.

Restricted to one of the following resolutions:

• 720 × 480 pixels, 24 / 1,001, 24, 30 / 1,001 or 30 frames / s
• 640 × 480 pixels, 24 / 1,001, 24, 30 / 1,001 or 30 frames / s
• 544 × 480 pixels, 24 / 1,001, 24, 30 / 1,001 or 30 frames / s
• 480 × 480 pixels, 24 / 1,001, 24, 30 / 1,001 or 30 frames / s
• 352 × 480 pixels, 24 / 1,001, 24, 30 / 1,001 or 30 frames / s
• 352 × 240 pixels, 24 / 1,001, 24, 30 / 1,001 or 30 frames / ss
• 720 × 576 pixels, 25 frames / s
• 544 × 576 pixels, 25 frames / s
• 480 × 576 pixels, 25 frames / s
• 352 × 576 pixel, 25 frames / s
• 352 × 288 pixels, 25 frames / s
• 352 × 576 pixel, 25 frames / s
• 352 × 288 pixels, 25 frames / s

MPEG-2 in ATSC and ISDB-T

Restricted to one of the following resolutions:

• 1920 × 1080 pixels, up to 60 fields / s (1080i)
• 1280 × 720 pixels, up to 60 frames / s (720p)
• 720 × 576 pixels, up to 50 fields / s, 25 frames / s (576i, 576p)
• 720 × 480 pixels, up to 60 fields / s, 30 frames / s (480i, 480p)
• 640 × 480 pixels, up to 60 frames / s

Note: 1080i is encoded with 1920 × 1088 pixel frames, however the last 8 lines are discarded before being displayed.

Patent retainers

Approximately 640 worldwide patents make up the complete intellectual property surrounding MPEG-2, these are held by around 20 corporations and one university:

• Alcatel
• Canon, Inc.
• Columbia University
• France Télécom (CNET)
• Fujitsu
• General Electric Capital Corporation
• General Instrument Corp.
• GE Technology Development, Inc.
• Hitachi, Ltd.
• KDDI Corporation (KDDI)
• Lucent Technologies
• LG Electronics Inc.
• Matsush
• Mitsubishi
• Nippon Telegraph and Telephone Corporation (NTT)
• Philips]]
• Robert Bosch GmbH
• Samsung
• Sanyo Electric Co. Ltd.
• Scientific Atlanta (today part of Cisco Systems)
• Sharp
• Sony
• Thomson Licensing SA
• Toshiba
• Victor Company of Japan, Limited (JVC)