ZR38000 ZR38521 ZR36120 ZR38521/ ZR38500 MK2744 - Datasheet Archive
AC-3 Audio, MPEG2 Video Combined On Ultra Dense Disc Enables Integration OfFull Motion Video Into PC Interactive Applications By
DVD Sparks Multimedia PCs AC-3 Audio, MPEG2 Video Combined On Ultra Dense Disc Enables Integration OfFull Motion Video Into PC Interactive Applications By Ohad Meitav, Zoran Corporation Today's PCs inherently include multimedia capabilities introducing sound and visual -effects into almost every applicationfrom computer games, video conferencing to video editing. With these new sound and video capabilities comes the need for large storage capacity. The DVD standard, recently introduced by Toshiba, Sony and other members of the DVD Consortium, was designed for storing this vast amount of digital video and audio information. With a phenomenal storage capacity 17 Gigabytes, a double-sided, of double-layered DVD can hold both the audio and video information for over 10 hours of full motionvideo on a single five inch DVD disc. This opens a whole new world of opportunities for video makers and PC applications. example, users can play For an interactive video or PC game withmultiple scenarios. PC games and other applications currently stored on several CDs be stored on a single DVD. But home entertainment, can publishing and computer games are only a few market segments for the new DVD technology. In addition to audio and video media, t DVD can be usedto store other he data. PC makers always craving data storage capacity will surely use it as an upgrade for the traditional CDto save storage space and the overall costs of storage media. To give a comparison ofthe information storage possibilities -one double-sided, double-layered DVD has rough the same storage capacity as 30 CDs. ly The audio and the video on the DVD are compressed with alg orithms that require plenty of computing powerto decode them. Today's most powerful CPUs find it difficult to handle this task by themselves, especially when there are other things to do concurrently such as handling Windows and running power-hungry applications (games with graphics and video). Thus dedicated DSPs are used to decode the information. The DVD standard adopts video and audio compression algorithms that provide supe rior video and audio quality. The video is compressed with the MPEG2 algorithm and the audio (is compressed) with Dolby AC-3 deliver 6 channels of surround sound. to The DVD provides many features and distinct advantages enhance the video quality that way beyond what the consumer is used to seeing. For example, the DVD standard supports a 16:9 aspect ratio, as opposed to mainstream 4:3 ratioso that movies can be easily , adapted to the TV screen without the need of cropping or letter-boxing. The DVD standard also provides much higher resolution than analog , more than twice that of NTSC television and true colors that do not interfere with the luminance information , . The DVD also offers advanced interactivity and navigation capabilities. Pausing, slow motion, branching,and virtually instantaneous cueing offer very productive ground for developing and playing interactive applications such as video games, educational applications and interactive movies. This i nteractivity cannot be achieved with serially accessed recording means uch as magnetic tapes. s Satellite and cable video broadcasting channels have also adopted the MPEG2 video compression standard. This wi increase the integration of new ll digital video player that s will playDVDs and receivelive video broadcasts. Compression Standards MPEG2 The Moving Pictures Expert Group (MPEG) has defined a method forthe compressed representation of digital video. The compression algorithm itself takes advantage of the similarity betweenconsecutive video frames. The principles of MPEG2 and MPEG1 are the same, but MPEG2 been extended to has address the multiprocessing needs of interlaced source materials. This makes MPEG2 more suitable than MPEG1 for applications such as satellite broadca sting, cable TV, HDTV and DVD. The MPEG2 standard is defined in terms of profiles where as each profile defines the features that are needed to support a group of applications. There are five profiles that define the sub-sampling (4:2:0, 4:2:2, etc.) of the bitstream. There are also four levels in this standard that define the image resolution and the maximum bit rate per profile. Most of the applications that use MPEG2, including DVD, support main profile and main level. The MPEG2 system defines two data stream hierarchies, Transport stream and Program stream. The Program stream is similar to MPEG System stream with some extensions 1 and is suitable for DVD data. The Tranport stream contains multiple Pogram streams s r and is suited formore error prone environment applications, mainly video broadcasting. Dolby Digital - AC-3 Dolby Digital (Dolby AC-3) is principally based on the psychoacoustical properties the of human hearing. The human hearing is such that when listening to a certain frequency at relatively high volume, sufficiently close frequencies at much lower volumes are masked and almost not heard. AC-3 divides the spectrum into frequency bands, optimized to the human hearing. In each band where there are audio signals masking the entire band, they are encoded and saved. Bands which do not contain masking audio signals are treated as coding noise and sharply filtered. With a sophisticated masking model and bit allocation scheme, AC-3 achieves extraordinary spectrum efficiency and preserves the origi nal recorded sound quality. The architecture for the first generation Dolby AC-3 six-channel decoder chip, the ZR38000 ZR38000, was co-developed by Zoran Corporation and Dolby Labs in 1991. Zoran's second-generation Dolby-certified AC-3 chips that have been shipping since 1995 target the needs of the emerging audio and audio/video consumer multimedia products and support 32, 44.1 and 48 kHz sampling frequenciesTypical bit rates include 384 kb/s for . 5.1-channels and 192 kb/s for two channels. DVD specifiesthe 5.1-channel formatfor NTSC countries When using a decoder with two-channel output, the 5.1 channels are . decoded and mixed, each channel according to its weight, to form a two channel output. The Zoran chip have additional MIPS left for user-customization of post processing audio algorithms (e.g. filtering, eliminating external circuitry, generation of special audio effects etc.) Dolby and Zoran are jointly bringing the Dolby Digital sound to the PC. Video On PC The capability to display video and play audio in the PC environment isenabling factor an for many multimedia PC applications, in particular for the DVD playback application. There are several possible architectures that take igital video and display it as video-in-ad window on a PC monitor. One architecture is based on an overlay device with a frame buffer. A video overlay device receives the digital video from one port and the currently displayed graphics image from another. It puts the video in a defined location on the graphics image and outputs analog RGB signals to the monitor. This architecture requires a dedicated overlay device and a display memory, which makes it relatively expensive. It used to be the dominant architecture in the old ISA based computers, but now is essentiallyobsolete. A dedicated video input port on the graphics accelerator suggests another scheme for transferring the digital video. The MPEG decoder, or any other digital video source, may drive the video port. The video source can be on the gra phics board or on another board connected with a dedic ted bus such as VMI, LPB, etc.The advantages of this scheme a compared to transferring the video over the PCI bus (see below) are obvious, the PCI bus is not loaded with video data and long bus latencies do not affect the video stream. However, the PCI bandwidth is sufficiently high for video data, and in a reasonably configured system very long bus latencies do not occur. Furthermore, there is no agreed upon standard that issupported by all or at leastthe majority of the graphics processor vendors in regard to the dedicated video bus. Another architecture that takes advantage of the high PCI bandwidth is shown in figure 1. Figure 1. Video Over The PCI Video Board Multimedia Controller PCI bus Display Memory Graphics Accelerator A video source such as an MPEG decoder is located on the video board. The Multimedia Controller masters the PCI bus and writes the digital video, with memory to memory transactions, to the graphics accelerator's on-screen or off-screen area in the display memory. If the video is written to the on-screen area it is immediately displayed without the accelerator's intervention. From the off-screen area the video is copied by the accelerator that can manipulate it by scaling, filtering and masking. The display memory address is obtained by calling Direct Draw or by other methods. The advantages of this architecture are its low cost (as an overlay device and a frame memory are not needed) and compatibility with most of the existing accelerators, both on graphics boards and on motherboards. The drawback of this scheme is that it demands that the graphics accelerator support linear addressing, and "good " PCI behavior from all other agents, meaning that nobody holds the bus for excessively long periods, prematurely aborts long transactions etc. However, as this scheme is becoming prevalent, more and more graphics accelerator vendors such as S3, A Number9, Matrox and others aresupporting it. TI, DVD4PC - A DVD Playback Implementation Fr PCs o In order to help OEMs reduce time-to market for developing DVD-enabled products, Zoran has developed a reference design board called DVD4PC. DVD4PC a PCI-PC is add in card that provides playback capability of MPEG2 program streams MPEG1 , and system streams. The audio is either AC-3 or MPEG1. The source, selectable by the user, can be a file stored on the hard disc, CD-ROM or DVD-ROM. Through a graphical user application such as MediaPlayer the user can play the source and perform control operations, such a stop, pause, seek, skip, etc. DVD4PC demonstrates s Zoran's ZR38521 ZR38521 AC-3 Decoder and ZR36 PCI Multimedia Controller. 120 DVD4PC takes advantage of the strengths of digital signal processors as well as the CPU's computing power and the high bandwidth of the PCI bus. The program stream parsing is done by the Pentium CPU while the elementary audio and video streams ar decoded by the on board DSPs. e The decoded audio goes to a DAC and is outputted to a pair of amplified speakers. The decoded video is transferred simultaneously to a video encoder, which generates composite and S-video, and to the graphics accelerator's display memory. Figure 2 is the block diagram of the DVD4PC. PCI interface The Zoran ZR36120 ZR36120 Multimedia Controller manages the communication between the host CPU and the DVD4PC. It masters the PCI bus in order to transfer video into a programmable destination in memory, and to acquire simultaneously the coded data from the system memory. With its generic bus interface, the GuestBus, the ZR36120 ZR36120 accommodates all the devices on the DVD4PC. A handshaking protocol enables the host to access the different devices on board. DVD4PC block diagram PCI bus STi3520A MPEG2 Video Decoder ZR36120 ZR36120 code PCI Multimedia Controller S-video output Video Encoder video clock video PLL AC3 code audio clock ZR38521/ ZR38521/ ZR38500 ZR38500 AC3 Audio DSP Audio DAC Audio Left / Right S/PDIF output On its video port, the ZR36120 ZR36120 receives YUV 4:2:2 digital video. The ZR36120 ZR36120 inclu des a color space converter,a pixel formatter that organizes the pixels according to the graphics device's mode of operation (i.e. 16 bits high color or 24 bits true color) a and smooth down-scaler The video is then written to the graphi memory to be displayed as . cs a video-in-a-w indow. Audio decoder DVD4PC accommodates either the ZR38500 ZR38500 or the ZR38521 ZR38521 audio DSPs. The Zoran ZR38521 ZR38521 is an AC-3 / MPEG1 audio decoder that does not require to external memory. The decoded AC-3 stream contains 5.1 channels of audio. Since most PCs have only two speakers, the AC-3 stream is down-mixed to two channels, and the output after the DAC is stereo left / right analog audio. The ZR38500 ZR38500 is a 5.1 channel AC-3 decoder that interfaces to an external SRAM. The external memory is used as data and program memory so, various programs can be loaded, such as audio post processing algorithms, surround audio effects and more. The ZR38500 ZR38500 is also capable of outputting the AC-3 stream in S/PDIF format. This feature is used for transferring the audio bitstream to a n external 5.1-channel AC-3 decoder . MPEG video decoder The SGS-Thomson STi3520A is the MPEG2 video decoder. It is capable of performing MPEG2 or MPEG1 video and MPEG1 audio decoding; however, on the DVD4PC only the video decoder is used. The video bitstream is fed into the STi3520A's 128-byte input buffer via an 8-bit asynchronous port. The maximum supported burst rate in this system, for up to 128 bytes, is 5.5 Mbytes/sec. The video decoder is a picture decoder, that is, it decodes a whole picture and then stops until instructed to decode the next picture p resent in the video bitstream. Host interrupts are generated by the MPEG2 decoder as a result of VSYNC, picture decoding and picture header detection events, the average rate is an interrupt per 10 msec. Clock Generation The clocks are generated by a Microclock MK2744 MK2744 PLL. 27 MHz and 13.5 MHz are needed for the video, multiples of 48 / 44.1 kHz for the audio. Generating the video and the audio clocks by the same PLL is important for maintaining the audio / video synchronization. Data Flow The MPEG2 stream is parsed into elementary video and packetized audio streams. The video bitstream is placed in a system memory buffer, to be acquired by the multimedia controller in a memory read burst. The video coded data is then written by the multimedia controller to the MPEG video decoder. The audio bitstream is transferred to the AC-3 decoder via the STi3520A which is working in audio bypass mode. This mode was originally designed for transferring PCM data directly to a DAC, however on the DVD4PC, an AC-3 coded stream is sent to the STi3520A instead of PCM data. A coded audio data buffer is allocated in the STi3520A's DRAM and the host maintains its fullness level. The STi3520A outputs the data "as is", to the ZR38521 ZR38521 that is connected to its serial port. Audio / Video synchronization One of the interesting problems in system is to ensureaudio / video synchronization, the especially since the audio and the video are decoded by two independent decoders. The monitoring task is done by the host CPU. The audio decoder receivespacketized a bitstream, it detects the Presentation Time Stamps that are present in some of the audio packet headers, and reports the latestdetected PTS back to the host.The video decoder, being actually a picture decoder, interrupts the host every picture header detection. This way the host knows how many pictures have been decoded. The host then normalizes this value and compare it to the audio PTS. If the video "runs ahead" the host instructs the video decoder to freeze a frame, if the video lags behind - to skip a frame. Since the audio and video clocks are locked, the synchronization is normally maintained without host intervention. The monitoring mechanism gets activated in cases of stream errors and after user operations like fast-search, seek, etc. What's next DVD will surely become an integral part of the multimedia PC andwill take it to new horizons. The architecture of the decoding and playback solution will also evolve. Windows will include another layer that interfaces video decoding and audio decoding drivers. The rationale behind this separation instead of having one software module that does the whole DVD decoding, is to be able to combine different audio channels with the same video channel. For example, sound track voice channel in Dutch to an English speaking video is found on the Internet. The playing application sends the MPEG2 video to the video driver, and the Dutch AC-3 compressed audio stream, instead of the English one, to the audio driver. Higher levels of integration will result in DVD-on-a-chip devices. This will further broaden the scope of DVD to platforms like portable computers, video game players, and portable DVD players. Zoran is working closely with industry leaders to meet the the specific requirements for new and exciting next-generation multimedia systems. About The Author Ohad Meitav is a system architect in Zoran's operations in Haifa, Israel. He completed a B.Sc. in computer engineering from the Technion, Israel Institute of Technology, in 1994. His professional areas of interest are MPEG systems, PC architecture, and parallel processing. In his spare time he enjoys flying aircraft.