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MPEG2whitepaper MPEG2whitepaper Document Transcript

  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems1 INTRODUCTION.......................................................................................................................... 2 1.1 MPEG IDEA AND STANDARD ...................................................................................................... 2 1.2 MPEG-2 DIGITAL VIDEO SPECIFICATIONS ....................................................................................... 2 1.3 THE WORLDWIDE MPEG-2 STANDARD .......................................................................................... 22 PROFILES AND LEVELS ............................................................................................................. 3 2.1 DESCRIPTION ........................................................................................................................... 3 2.2 PROFILES ............................................................................................................................... 3 2.2.1 Description of the five profiles .......................................................................................... 3 2.3 LEVELS .................................................................................................................................. 4 2.3.1 Description of a level....................................................................................................... 4 2.3.2 Level according quality .................................................................................................... 4 2.4 PRACTICAL USAGE OF LEVELS AND PROFILES ................................................................................ 5 2.4.1 Typical Main Level bit rates for common applications ......................................................... 5 2.4.2 Typical picture size and application .................................................................................. 53 COMPRESSION .......................................................................................................................... 7 3.1 THE ENCODING PROCESS ............................................................................................................ 7 3.1.1 Compression details........................................................................................................ 8 3.2 GROUP OF PICTURES (GOP) ....................................................................................................... 9 3.2.1 GOP length for distribution purposes ................................................................................ 9 3.2.2 GOP length for editing purposes......................................................................................10 3.3 MOTION ESTIMATION PREDICTION .................................................................................................104 VARIABLE BIT RATE FOR VIDEO ENCODING.............................................................................12 4.1 FIXED BIT RATE ENCODING..........................................................................................................12 4.2 ADVANTAGES OF USING A VARIABLE BIT RATE ...............................................................................125 MPEG AUDIO.............................................................................................................................146 MPEG-2 AND DVD......................................................................................................................157 DISCUSSING MPEG-2 I, IP, IBP ................................................................................................16 7.1 MPEG-2 I FRAMES COMPARED .................................................................................................16 7.2 MPEG-2 IP METHOD ..............................................................................................................17 7.3 MPEG-2 IBP METHOD............................................................................................................19 7.4 A COMPARISON OF THE INDIVIDUAL COMPRESSION METHODS ............................................................20 7.5 SELECTION OF A SUITABLE METHOD ............................................................................................20 MPEG-2 White Paper - Pinnacle Page:1/1 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems1 Introduction1.1 MPEG idea and standard The Moving Pictures Experts Group abbreviated MPEG is part of the International Standards Organisation (ISO), and defines standards for digital video and digital audio. The primal task of this group was to develop a format to play back video and audio in real time from a CD1. Meanwhile the demands have raised and beside the CD the DVD2 needs to be supported as well as transmission equipment like satellites and networks. All this operational uses are covered by a broad selection of standards. Well known are the standards MPEG-1, MPEG-2, MPEG-4 and MPEG-7. Each standard provides levels and profiles to support special applications in an optimised way.1.2 MPEG-2 digital video specifications MPEG-2 video is an ISO/IEC3 standard that specifies the syntax and semantics of an enclosed video bitstream. These include parameters such as bit rates, picture sizes and resolutions which may be applied, and how it is decoded to reconstruct the picture. What MPEG-2 does not define is how the decoder and encoder should implemented, only that they should be compliant with the MPEG-2 bitstream. This leaves designers free to develop the best encoding and decoding methods whilst retaining compatibility. The range of possibilities of the MPEG-2 standard is so wide that not all features of the standard are used for all applications.1.3 The worldwide MPEG-2 standard The MPEG-2 video standard allows MPEG-2 compatible equipment to inter-operate, because the bitstreams are standardized. However, the way the actual encoding process is implemented to generate the bitstream is up to the encoder designer. Therefore, all equipment will not necessarily produce the same quality video (at a given bit rate) there will be a range of products available, at different price levels, which the consumer can choose from to suit their own application.1 CD: Compact Disk2 DVD: Digital Versatile Disk3 ISO: International Standards Organization, IEC: International Electrotechnical Commission MPEG-2 White Paper - Pinnacle Page:2/2 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems2 Profiles and Levels2.1 Description MPEG-2 video is a family of systems, each having an arranged degree of commonality and compatibility. It allows four source formats, or ‘Levels’, to be coded, ranging from Limited Definition (about today’s VCR4 quality), to full HDTV 5 – each with a range of bit rates. In addition to this flexibility in source formats, MPEG-2 allows different ‘Profiles’. Each profile offers a collection of compression tools that together make up the coding system. A different profile means that a different set of compression tools is available.2.2 Profiles There are currently five profiles in the MPEG-2 system. Each profile is progressively more sophisticated and adds additional tools to the previous profile. This means that each will do more than the last, but is likely to cost more to make, and thus cost more to the customer.2.2.1 Description of the five profiles • The profile which has the fewest tools is called the Simple Profile. The Simple profile offers the basic toolkit for MPEG-2 encoding. This is intra and predicted frame encoding and decoding (see page 7 for more details) with a color sub sampling of YUV 6 4:2:0. • The following profile is called Main Profile. It has all the tools of the Simple Profile plus one more (termed bi-directional prediction). It will give better (maximum) quality for the same bit rate than the Simple Profile, but will cost more IC7 surface area. A Main Profile decoder will decode both Main and Simple Profile-encoded pictures. This backward compatibility pattern applies to the succession of profiles. A refinement of the Main Profile, sometimes unofficially known as Main Profile Professional Level or MPEG 422, allows line-sequential colour difference signals (4:2:2) to be used, but not the scaleable tools of the higher Profiles. • The two Profiles after the Main Profile are, successively, the SNR8 Scaleable Profile and the Spatially Scaleable Profile. These add tools which allow the coded video data to be partitioned into a base layer and one or more ‘top-up’ signals. The top-up signals can either improve the noise (SNR Scalability) or the resolution (Spatial Scalability). These Scaleable systems may have interesting uses. The lowest layer can be coded in a more robust way, and thus provide a means to broadcast to a wider area, or provide a service for more difficult reception conditions. Nevertheless there will be a premium to be paid for their use in receiver complexity. Owing to the added complexity, none of the Scaleable Profiles is supported by4 VCR: Video Cassette Recorder5 HDTV: High Definition Television6 YUV: Signal with the components Luminance (Y) and Color Difference (U,V)7 IC: Integrated Circuit8 SNR: Signal to Noise Ratio MPEG-2 White Paper - Pinnacle Page:3/3 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems DVB9. The inputs to the system are YUV component video. However, the first four profiles code the colour difference signals line-sequentially. • The final profile is the High Profile. It includes all the previous tools plus the ability to code line-simultaneous colour-difference signals. In effect, the High Profile is a ‘super system’, designed for the most sophisticated applications, where there is no constraint on bit rate. Profile SIMPLE MAIN 422*) SNR SPATIALLY HIGH Tool SCALABLE SCALABLE I-Frames ü ü ü ü ü ü P-Frames ü ü ü ü ü ü B-Frames ü ü ü ü ü 4:2:2 ü ü ü ü SNR scalable ü ü ü Spatially ü ü scalable Table 1: MPEG-2 Profiles and Coding Tool Functionalities *)Refinement of the Main Profile2.3 Levels2.3.1 Description of a level A level is the definition for the MPEG standard for physical parameters such as bit rates, picture sizes and resolutions. There are four levels specified by MPEG2: High level, High 1440, Main level, and Low level. MPEG-2 Video Main Profile and Main level has sampling limits at ITU-R10 601 parameters (PAL and NTSC). Profiles limit syntax (i.e. algorithms) whereas Levels limit encoding parameters (sample rates, frame dimensions, coded bitrates, buffer size etc.). Together, Video Main Profile and Main Level (abbreviated as MP@ML) keep complexity within current technical limits, yet still meet the needs of the majority of applications. MP@ML is the most widely accepted combination for most cable and satellite systems, however different combinations are possible to suit other applications.2.3.2 Level according quality Levels are associated with the source format of the video signal, providing a range of potential qualities, from limited definition to high definition: • Low Level has an input format which is one quarter of the picture defined in ITU-R Recommendation BT.601. • Main Level has a full ITU-R Recommendation BT. 601 input frame.9 DVB: Digital Video Broadcasting10 ITU-R: International Telecommunications Union - Recommendation MPEG-2 White Paper - Pinnacle Page:4/4 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems • High-1440 Level has a High Definition format with 1440 sample/line. • High Level has a High Definition format with 1920 samples/line. Level Frame size Maximum Significance (PAL / NTSC) Bitrate Low 352x288 4 Mb/s CIF, consumer tape equiv. 352x240 Main 720x576 15 Mb/s ITU-R 601, Studio TV 720x480 High 1440 1440x1152 60 Mb/s 4x 601, consumer HDTV 1440x1080 High 1920x1152 80 Mb/s prod. smpte 1920x1080 Table 2: The four Levels with frame size and maximum bit rate defined for each level2.4 Practical usage of Levels and Profiles2.4.1 Typical Main Level bit rates for common applications MPEG-2 video at the appropriate storage medium can easily adjusted to the quality of many of the current video distribution formats. Even at a low bit rate it still maintains a perfect quality. The following table provides an overview about bit rates compared to current distribution formats. The MPEG-2 video is coded ML@MP with IPB frames. Coded rate (IBP) Application 2 MBit/s Equivalent to VHS 4 MBit/s PAL Broadcast Quality 10 Mbit/s DVD Quality 15 Mbit/s Equivalent to DV Quality Table 3: MPEG-2 bit rates compared to common video distribution formats2.4.2 Typical picture size and application MPEG-2 defines a range of picture sizes to suit a range of different applications: It shows also that MPEG-2 video is still compatible with the current video formats. PAL NTSC 352x288 352x240 SIF, CD White Book Movies, Video Games 352x576 352x480 Half Horizontal Resolution (VHS equiv.) MPEG-2 White Paper - Pinnacle Page:5/5 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems 544x576 544x480 Laserdisk, D2, Band Limited Broadcast -- 640x480 Square Pixel NTSC 720x576 720x480 ITU-R 601, D1 Table 4: PAL and NTSC resolutions which MPEG-2 video supports Summary Profiles limit syntax (compression tools, i.e. algorithms) Levels limit encoding parameters (sample rates, frame dimensions, coded bitrates, buffer size etc.) MPEG-2 White Paper - Pinnacle Page:6/6 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems3 Compression3.1 The encoding process Encoding of video information is achieved by using two main techniques. These are termed spatial and temporal compression. Spatial compression involves analysis of a picture to determine redundant I information within that picture, for example by discarding frequencies that are not visible to the human eye. Temporal compression is achieved P by only encoding the difference between successive pictures. P Imagine a scene where at first there is no movement, then an object moves I across the picture. The first picture in the sequence contains all the information required until there is any movement, so there is no need to encode any of the information after the first picture until the movement occurs. Thereafter, all that needs to be encoded is the part of the picture that contains movement. The rest of the scene is not effected by the moving object because it is still the same as the first picture. The means by which is determined how much movement is contained between two successive pictures is known as motion estimation prediction. The information obtained from this process is then used by motion compensated prediction to define the parts of the picture that can be discarded. This means that pictures cannot be considered in isolation. A given picture is constructed from the prediction from a previous picture, and may be used to predict the next picture. There is also the need to have pictures which are not used in any reference for random access. Therefore MPEG-2 defines three picture types: I (Intraframe) pictures. These are encoded without reference to another picture to allow for random access P (Predictive) pictures are encoded using motion compensated prediction on the previous picture therefore contain a reference to the previous picture. They may themselves be used in subsequent predictions MPEG-2 White Paper - Pinnacle Page:7/7 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems B (Bi-directional) pictures are encoded using motion compensated prediction on the previous and next pictures, which must be either a B or P picture. B pictures are not used in subsequent predictions. The I, P and B pictures can be formed into a group of pictures (GOP). Each picture type (I, P, B) provides increased opportunity of redundancy. An I picture is encoded with little compression (only spatially redundant information). P and B pictures also use motion compensation to remove temporally redundant information. B pictures offer the most compression. Typical bit allocations are shown below: Picture Type Bit Allocation Bit Allocation 30 Hz SIF @ 1.15 Mbit/sec 30 Hz ITU-R 601@ 4 MBit/sec Intra 150 Kbit 400 KBit Predictive 50 Kbit 200 KBit Bi-directional 20 Kbit 80 KBit Table 5: Pictures of a Standard Test Sequence with a I-Frame distance of 15 and a P-Frame distance of 33.1.1 Compression details Spatial compression is achieved in practice by use of a DCT which converts the information in the picture to be e ncoded in the frequency domain. This transform is used to remove redundant information within the picture itself, by removing frequencies with negligible amplitudes and rounding frequency co-efficients to standard values. At higher frequencies, contrast is less perceptible by the human eye, therefore these frequencies we cannot detect can be removed. More compression can also be achieved by using a process called run length encoding. This is an operation that searches for regularly occurring patterns in the frequency information obtained from the DCT. If a pattern is detected, it can be replaced by a shorter representative pattern, providing even more compression efficiency. MPEG-2 White Paper - Pinnacle Page:8/8 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems s0 y1 b1 + DCT Q1 VLC IDC + MCP (i)DCT: (Inverse) Discrete Cosine Transformation Q1: Quantisation VLC: Variable Length Coding MCP: Motion Compensation Prediction Figure 1: Generalized MPEG-2 Encoder Motion compensated prediction is used to exploit redundant temporal information that is not changing from picture to picture. The images in a video stream do not generally change much within small time intervals. The idea of motion compensated prediction is to encode a video frame based on other video frames temporally close to it.3.2 Group of pictures (GOP) This is the grouping of I and P, I and B or I, B and P pictures into a specified sequence known as a group of pictures (GOP). The group must start and end with an I picture to allow for random access to the group, and contains P and/or B pictures in between in a specified sequence (determined by the designer). A group can be made of different lengths to suit the type of video being encoded and the application the video is used for.3.2.1 GOP length for distribution purposes For example it is better to use a shorter group lengths for a film which contains a lot of fast moving action with complex scenes. A group lengths is typically between 8-24 pictures. Commonly used GOP sizes are 12 for 50 Hz systems, 16 for 60 Hz systems. GOPs are optional in an MPEG-2 bitstream, but are mandatory in DVD video, to achieve an SMPTE 11 timebase. A bitstream with no GOP header can be directly accessed at a specific point using the sequence header.11 SMPTE: Society of Motion Picture and Television Engineers MPEG-2 White Paper - Pinnacle Page:9/9 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems I B B P B B P B B P B B P B B Figure 2: Typical GOP structure and size for a IBP encoded video stream used for video distribution formats3.2.2 GOP length for editing purposes When it comes to editing typically IP-Frames are used. Some systems who not really need to take the advantage of MPEG-2 choose I-Frames only. A typical IP GOP length for non linear postproduction can be set to 3 or 4 frames. Any additional P frame will not gain a significant decrease in data rate. I P P P Figure 3: Typical GOP structure and size for a IP encoded video stream used for video editing formats3.3 Motion estimation prediction Motion estimation prediction is a method of determining the amount of movement contained between two pictures. This is achieved by dividing the picture to be encoded into sections known as macroblocks. The size of a macroblock is 16 x 16 pixels. Each macroblock is searched for the closest match in the search area of the picture it is being compared with. Motion estimation prediction is not used on I pictures, however B and P pictures can refer to I pictures. For P pictures, only the previous picture is searched for matching macroblocks. In B pictures both the previous and next pictures are searched. When a match is found, the offset (or motion vector) between them is calculated. The matching parts are used to create a prediction picture, by using the motion vectors. The prediction picture is then compared in the same manner to the picture to be encoded. Macroblocks which have a match have already been encoded, and are therefore redundant. Macroblocks which have no match to any part of the search area in the picture to be encoded represent the difference between the pictures, and these macroblocks are encoded. Summary Encoding is achieved by using spatial and temporal compression – this compression is GOP based Two methods are used in conjunction when encoding a GOP: 1. Intra-frame compression: compression of complete single frames MPEG-2 White Paper - Pinnacle Page:10/10 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems 2. Inter-frame compression: Check for correlations between subsequent frames, discard redundant information, store the rest -> This results in I, P and B frames MPEG-2 White Paper - Pinnacle Page:11/11 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems4 Variable bit rate for video encoding In any given video section, certain parts contain more movement than others or more fine detail. For example a clear blue sky is simpler to encode than a picture of a tree. As a result the number of bits needed to faithfully encode without artefacts varies with the video material. In order to encode in the best possible way, it is advantageous to save bits from the simple sections and use them to encode complex ones. This is, in a simple way, what variable bit rate encoding does, however the process by which the bit rates are calculated is complex. Variable bit rate encoding can be carried out in one or two passes of the video data. For fixed size storage applications such as DVD12, the amount of encoded video information must be known in advance, therefore two passes of the video information are required. This ensures that the amount of data is not too small (quality compromised) or too large (not enough storage space). The first pass is used to analyse and store encoding information about the video data, the second pass uses the information to perform the actual encoding. Where the amount of encoded data produced is not so critical, encoding can be carried out in one pass of the input video.4.1 Fixed bit rate encoding For some applications, it is necessary to transmit the encoded video information with a fixed bit rate. For example, in broadcast mediums (satellite, cable, terrestrial etc.), practical limitations mean that current transmission is restricted to using a fixed bit rate. This is why fixed bit rate MPEG-2 encoders are available. It is true that a fixed bit rate encoder is not as efficient as the variable bit rate system, however the MPEG-2 system still provides very high quality video for both encoding methods. Very importantly, fixed bit rate encoding can also be carried out in real time, i.e. one pass of the video information. For live broadcasts, and satellite linkups etc. the real time encoding capability is essential.4.2 Advantages of using a variable bit rate The advantage of using a variable bit rate is mainly the gain it gives in encoding efficiency. For fixed storage mediums (e.g. DVD) the variable bit rate is ideal. By reducing the amount of space needed to store the video (whilst retaining very high quality), it leaves more space on the medium for inclusion of other features e.g. multiple language soundtracks, extra subtitle channels, interactivity, etc. The other important feature of the variable bit rate system is that it gives constant video quality for all complexities of program material. A constant bit rate encoder provides variable quality. Summary Variable bit rate = constant quality Constant bit rate = variable quality12 DVD: Digital Versatile Disk MPEG-2 White Paper - Pinnacle Page:12/12 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems MPEG-2 White Paper - Pinnacle Page:13/13 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems5 MPEG Audio Audio compression is based on the principle of leaving out those parts of the sound that are imperceptible to the human ear. An audio CD, for example, has a quantizing depth of 16 bits at 44,000 samples per second. This is enough to eliminate background noise in even the quietest passages or breaks. Background noise present in loud passages would be covered up by the music, making it possible to reduce the resolution without an audible loss in quality. So depending on the characteristics of the music, the resolution can be more or less reduced in order to achieve data reduction and better rates of compression. The MPEG standard provides for three audio compression methods, audio layers 1 through 3. Each layer is compatible with the format of the layer(s) below it and has its own file name extensions. As with MPEG video, however, this standard stipulates the format and decoder for each layer, but not the encoding algorithm. Thus it is possible to develop varying algorithms that also deliver varying results and levels of quality. Layer 1 is the simplest version with the lowest rate of compression. The standard calls for a bit rate of 192 KBits per second and audio channel. Layer 2 is a compromise between sound quality and the complexity of the encoding algorithm. The specification for this layer calls for up to 128 KBits per second and channel. In stereo, therefore, the targeted rate of 250 KBits per second is attained. This method is generally used in audio in MPEG movies. Layer 3 is for low bit rates up to 64 KBits per second and channel. This layer is intended to achieve maximum sound quality at minimal bit rates. It is primarily used in digital connections such as ISDN. MPEG-2 White Paper - Pinnacle Page:14/14 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems6 MPEG-2 and DVD The characteristics of the DVD data medium and the MPEG-2 video codec make a good match when it comes to permanent storage of video with long playing times and high quality. The technical characteristics of DVDs and DVD drives may serve as outline conditions for assessing the quality and data rate aspects. CD DVD AV Format 74 minutes of digital audio 135 minutes of MPEG-2 video Capacity 650 MB 4.7 GB Transfer rate 150 KB/s 600 KB/s Table 6 : CD and DVD compared Capacity 1 side 2 sides Dual Layer DVD-ROM Read only Memory e.g., DVD Video 4.7 GB 9.4 GB 17 GB DVD-R Write Once 3.95 GB 7.9 GB - DVD-RAM Rewritable 2.6 GB 5.2 GB 5.6 GB Table 7: The storage capacities of the various DVD formats Even if the transfer performance of future DVD drives increases considerably and the capacity of the data medium can be further increased, DVD video with a maximum of 600 KB/s will probably become standard over the long term and become the higher-quality, digital counterpart of the VHS cassette. To produce video for this data medium, the final product should have a data rate not exceeding 600 KB/s, in order to guarantee compatibility with players. The MPEG-2 IBP method is predestined for this data rate. It attains the necessary compression. The productions are always saved in one continuous file, which is then prepared for the data medium by DVD authoring software. The Production Process Step Format Recording 422P@ML, IP Frames Editing 422P@ML, IP Frames Rendering ML@MP, IBP Frames DVD Authoring ML@MP, IBP Frames MPEG-2 White Paper - Pinnacle Page:15/15 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems7 Discussing MPEG-2 I, IP, IBP7.1 MPEG-2 I Frames Compared MPEG-2 Intra frame compression Raw (uncompressed) 810 KB per 720 PAL frame, Mbit/s: 158 MB/s: 19.76 Compression ratio: 5:1 I I I 162 KB per PAL Bild, Mbit/s: 32 MB/s: 4 Motion JPG compression Uncompressed 810 KB pro 720 PAL frame, Mbit/s: 158 MB/s: 19,76 Compression ratio: 5:1 MJPG MJPG MJPG 162 KB per PAL frame, Mbit/s: 32 MB/s: 4 DV compression Compression ratio: 5:1 Exactly 150 KB per PAL frame Mbit/s: 29 MB/s: 3.6 DV DV DV MPEG-2 White Paper - Pinnacle Page:16/16 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems All frames were encoded individually. Intraframe compression. At a compression ratio of 5:1 or higher, all data rates are considerably higher than 3 MB/s or 25 Mbit/s.7.2 MPEG-2 IP MethodA method that uses forward references. P-Frames are so-called predicted frames that point tothe future. The IPPP method starts the compression procedure for the group of pictures with a compressed individual frame I (I Frame) In the next step, a P frame is generated that contains a motion vector for the car I P object – the only area of the picture that has moved. The part of the scene that was covered by the car I P before and now is visible is copied from the original material to the P- frame. I P P MPEG-2 White Paper - Pinnacle Page:17/17 29-Feb-00 The procedure is repeated for additional
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems MPEG-2 White Paper - Pinnacle Page:18/18 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems7.3 MPEG-2 IBP MethodMethod that uses forward and backward references. B frames are so-called bi-directionalframes, that point to the future and the past. The IBP method starts the compression procedure for the group of images with a compressed individual frame (I- I frame) In the next step, the last frame of a GOP is generated as a P-Frame that contains a I P movement vector for the auto object as well as that area of the scenery that was previously hidden and is now visible. The B frames are set up by saving I B P movement vectors for the objects in motion. The B frames are I B P completed by copying previously hidden areas from the future MPEG-2 White Paper - Pinnacle Page:19/19 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle Systems7.4 A Comparison of the Individual Compression Methods MJPEG DV MPEG2 MPEG2 MPEG2 MPEG2 I-Frame IP IB IBP Editability good good good good good difficult Data rate 4..10 3.6 4..6 2 2 0.5..1.5 MB/s MB/s MB/s MB/s MB/s MB/s Com- 2..5 : 1 5:1 3..6 : 1 9:1 9:1 15..30 :1 pression7.5 Selection of a Suitable Method For non-linear video editing on standard computers, a method is required with a data rate that is less than the maximum bandwidth offered by these systems. Of course, this threshold varies from one computer to the next and is higher with high-performance systems. This is why the threshold value should be determined empirically. The miroVIDEO DC50 can be used as a known system load. It is can process up to 7 MB/s (56 Mbit/s) and marks the performance threshold of many computer configurations. Single Stream Maximum Bandwidth: 50 Mbits/s A real-time editing system must deliver the same quality but be capable of showing two videos simultaneously. The only systems even worthy of consideration are those with compression that reduces the data rate by at least half with negative effects on quality. The DV method nearly fulfills this demand, but takes it for granted that the necessary bandwidth will still be always be achieved, since the data rate is fxed. To ensure satisfactory operation, i only selected systems should be used for a DV Dual Stream system. The MPEG-2 IP method offers ideal preconditions for dual-stream operation on nearly all computers. Moreover, the adjustable data rate permits fine tuning. At a maximum data rate of 25 Mbit/s video channel, Dual Stream operation with real-time video effects is possible on modern computers. Dual Stream Maximum bandwidth: 2 x 25 Mbit/s MPEG-2 White Paper - Pinnacle Page:20/20 29-Feb-00
  • MPEG-2 White Paper - Pinnacle technical documentation -Vers.: 0.5 Pinnacle SystemsOften used abbreviations422P@ML 422 Profile at Main Level – MPEG 422CD Compact DiskDCT Discrete Cosines TransformationDVB Digital Video BroadcastingDVD Digital Versatile DiskHDTV High Definition TelevisionIC Integrated CircuitISO International Standards OrganisationITU International Telecommunications UnionJPEG Joint Picture Expert GroupMP@ML Main Profile at Main LevelMPEG Moving Pictures Experts GroupMPEG 422 422 Profile at Main Level, Studio MPEGMPEG-2 ISO Standard 13818RLE Run Length EncodingSMPTE Society of Motion Picture and Television EngineersSNR Signal to Noise RatioVCR Video Cassette RecorderYUV Signal incorporating the components Luminance (Y) and Color Difference (U,V) MPEG-2 White Paper - Pinnacle Page:21/21 29-Feb-00