IntroductiontMyn1 Introduction MPEG, Moving Picture Experts Group was started in 1988 as a working group within ISO/IEC with the aim of defining standards for digital compression of audio- visual signals. MPEG’s first project, MPEG-1 was published in 1993 as ISO/IEC In general MPEG is asymmetrical process: it has been estimated that encoding needs 100 times more processing power compared to the decoding process.

IntroductiontMyn2 MPEG-1 consists of six parts: systemISO/IEC videoISO/IEC audioISO/IEC low bit rate audioISO/IEC conformance testingISO/IEC simulation softwareISO/IEC

IntroductiontMyn3 ”Coding of moving pictures and associated audio for digital storage media” The original goal was playback of digital audio and video using a standard CD with a bit rate of Mbits/sec. MPEG 1 was designed to handle progressive (also referred to as noninterlaced) video. MPEG1 uses a family of three audio coding schemes, called Layer 1, Layer 2 and Layer 3, with increasing complexity and sound quality. The three layers are hierarchical: a Layer 3 decoder handles Layers 1, 2 and 3 and so on…

IntroductiontMyn4 All layers support 16-bit digitized audio using 16 (only MPEG 2), (only MPEG 2), 24 (only MPEG 2), 32, 44.1 or 48 kHz sampling rates. Layers work typically with bit rates: –Layer1: kbits/sec –Layer 2: kbits/sec –Layer 3: kbits/sec Two audio channels are supported with four modes of operation: –normal stereo –joint(intensity and/or ms) stereo –dual channel mono –single channel mono

IntroductiontMyn5 For normal stereo, one channel carries the left audio signal and one channel carries the right audio channel. For intensity stereo (supported by all layers) high frequencies (above 2 kHz) are combined. The stereo image is preserved but only the temporal envelope is transmitted. For ms stereo (supported by Layer 3), one channel carries the sum signal (L+R) and the other the difference (L-R) signal.

IntroductiontMyn6 To determine which layer should be used for a specific application, look at the available bit rate, as each layer was designed to support certain bit rates with a minimum degradation of sound quality. Layer 1, a simplified version of Layer 2, has a target bit rate of about 192 kbits/sec per channel or higher. Layer 2 is identical to MUSICAM, and has a target bit rate of about 128 kbits/sec per channel. –Masking-pattern adapted Universal Subband Integrated Coding and Multiplexing

IntroductiontMyn7 Layer 3 (also known as mp3) merges the best ideas of MUSICAM and ASPEC and has a target bit rate of about 64 kbits/sec per channel. –Adaptive Spectral Perceptual Entropy Coding

IntroductiontMyn8 All layers use a coding scheme based on psychoacoustic principles – in particular, ”masking” effect where, for example, a loud tone at one frequency prevents another, quieter, tone at a nearby frequency from being heard. Adjusting the noise floor reduces the amount of needed data, enabling further compression. CDs use 16 bits of resolution to achieve a signal-to- noise ratio (SNR) of about 96 dB, which just happens to mach the dynamic range of hearing pretty well.

IntroductiontMyn9 If 8-bit resolution were used, there would be a noticeable noise during silent moments in the music. However, noise isn’t noticed during loud passages due to the masking effect, which means that around a strong sound you can raise the noise floor since the noise will be masked anyway. For a stereo signal, there usually is redundancy between channels.

IntroductiontMyn10 Table 1 lists some of the constrained parameters. The CPB (Constrained Parameters Bitstream) is a limited set of sampling and bit rate parameters designed to standardize buffer sizes and memory bandwidths, allowing a nomimal guarantee of interoperability for decoders and encoders, while still addressing the widest possible range of applications.

IntroductiontMyn11 horizontal resolution vertical resolution picture area, number of macroblocks picture rate pel rate, number of macroblocks/s bit rate max 768 samples (pixels) max 1,856 Mbps max 576 scan lines max 396 macroblocks max 396*25 macroblocks per second max 30 frames per second Table 1. Some of the constrained parameters for MPEG 1.

IntroductiontMyn12 The CPB limits video to 396 macroblocks (396*16*16 = pixels). Therefore, MPEG 1 video is typically coded at SIF resolutions of 352*240 or 352*288. SIF, Standard Input Format: 352 (horizontal)*240 (vertical)*29,97 (fps), NTSC 352 (horizontal)*288 (vertical)*25,00 (fps), PAL

IntroductiontMyn13 MPEG 1 video data uses the 4:2:0 format shown in Figure 1.

IntroductiontMyn14 Active line number = Y sample = Calculated Cb, Cr sample Figure 1. Sampling for 4:2:0 MPEG 1.

IntroductiontMyn15 MPEG 2, ”Generic coding of moving pictures and associated audio information”, extends MPEG 1 to cover a wider range of applications. The primary application targeted during the definition process was all-digital transmission of broadcast- quality video at bit rates of 4-9 Mbits/sec. MPEG 2 is an ISO/IEC standard, and consists of nine parts:

IntroductiontMyn16 systemsISO/IEC video ISO/IEC audio ISO/IEC conformance testing ISO/IEC software simulation ISO/IEC DSM-CC extensions ISO/IEC (Digital Storage Media Command and Control) advanced audio coding ISO/IEC (Dolby Digital 5.1) RTI extension ISO/IEC (Real Time Interface) DSM-CC conformance ISO/IEC

IntroductiontMyn17 Figure 1 illustrates the positioning of samples for the 4:2:0 format. 4:2:0 implements a 2:1 reduction of and in both the vertical and horizontal directions. To display 4:2:0 data, it is first converted to 4:4:4 data, using interpolation to generate the new and samples. Actually MPEG 2 4:2:0 is not same as MPEG 1, see the spatial relationships between luminance and color difference samples.

IntroductiontMyn18 Active line number = Y sample = Calculated Cb, Cr sample Figure 1. 4:2:0 sampling forMPEG 2. The sampling positions on the active scan lines of a progressive or noninterlaced picture.

IntroductiontMyn19 Figure 2 illustrates the positioning of samples for 4:2:2 format. For every two horizontal Y samples, there is one and one sample. Each sample is typically 8 bits (consumer applications) or 10 bits (pro-video applications) per component. Each sample therefore requires 16 bits (or 20 bits for pro-video applications), usually formatted as shown in Figure 3.

IntroductiontMyn20 Active line number = Y sample = Calculated Cb, Cr sample Figure 2. 4:2:2 sampling for MPEG 2. The sampling positions on the active scan lines of a progressive or noninterlaced picture. Co-sited sampling.

IntroductiontMyn21 Y7-0 Y6-0 Y5-0 Y4-0 Y3-0 Y2-0 Y1-0 Y0-0 CB7-0 CB6-0 CB5-0 CB4-0 CB3-0 CB2-0 CB1-0 CB0-0 SAMPLE 0 SAMPLE 1 SAMPLE 2 SAMPLE 3 Y7-1 Y6-1 Y5-1 Y4-1 Y3-1 Y2-1 Y1-1 Y0-1 Y7-2 Y6-2 Y5-2 Y4-2 Y3-2 Y2-2 Y1-2 Y0-2 Y7-3 Y6-3 Y5-3 Y4-3 Y3-3 Y2-3 Y1-3 Y0-3 CB7-2 CB6-2 CB5-2 CB4-2 CB3-2 CB2-2 CB1-2 CB0-2 CR7-0 CR6-0 CR5-0 CR4-0 CR3-0 CR2-0 CR1-0 CR0-0 CR7-2 CR6-2 CR5-2 CR4-2 CR3-2 CR2-2 CR1-2 CR0-2 Figure 3. Frame buffer formatting in MPEG 2 4:2:2. -0 = SAMPLE 0 DATA -1 = SAMPLE 1 DATA -2 = SAMPLE 2 DATA -3 = SAMPLE 3 DATA

IntroductiontMyn22 For broadcast applications sufficient chrominance resolution can be provided with the 4:2:0 sampling. This method of sampling is generally accepted as the most applicable level and profile for MPEG 2, and is termed Main Profile at Main Level or Figure 4 illustrates MPEG 2 4:2:0 sampling in Digital TV environment.

IntroductiontMyn23 Active line number [4] [8] = Y sample = Calculated Cb, Cr sample Figure 4. Sampling 4:2:0 for MPEG 2. The sampling positions on the active scan lines of an interlaced picture (top_field_first = 1). [2] [6] [] = Field N+1 FIELD N FIELD N+1