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A production workstation is a system of hardware and software components you can use to create digital media. For example, a workstation for creating Microsoft® Windows Media®-based content may be as simple as a computer and video camera for streaming live traffic conditions. More complex workstations can be part of a complete audio and video production facility. The type of production workstation you put together depends on your needs, your desired digital media quality, and your budget.

This article describes what you need to build a workstation for capturing and encoding high-quality, high-bandwidth files that can play back full frame at the original frame rate. With Windows Media Encoder and Windows Media Encoding Script, you can create high-bandwidth files that can be downloaded or streamed over a broadband network. With Windows Media Capture 9 Series you can create uncompressed AVI files with which you can create Windows Media files in the encoder. The features and codecs in these capture and encoding tools enable you to create content that approaches DVD quality at a fraction of the bit rate and file size.

To capture and encode high-quality content, a workstation must be capable of high-quality analog-to-digital conversion. In addition, the computer must have the speed and memory to handle far more than the typical number of bits per second. The initial hardware investment may be higher than the cost of a low-bandwidth system, but the results are well worth it if you need high quality.

This article provides recommendations for a minimum and an optimal system for encoding Windows Media-based content. The recommendations also take into account system usage; that is, a computer used to capture video must have a great deal more speed and memory than one used for file-to-file conversions. For detailed recommendations, see the Hardware Recommendations section of this article.

Special Considerations for High Bandwidth

To take advantage of the high-bandwidth features and codecs, you need to be able to capture audio and video at its highest quality. A computer that can capture a small image size at 15 frames per second may not be able to handle video with four times the image size and twice the frame rate.

When video is converted from analog to digital, each frame is broken up into hundreds of pixels. Each pixel is represented by one or more bytes that represent the color of that small area of the image. Each video conversion requires a certain amount of computer memory and computation time. The higher the quality of video, the greater the number of frames per second; the larger the image size, the greater the number of pixels that must be converted in a given period of time. For example, when capturing video at 30 frames per second, the computer must not only be able to handle many pixel conversions, it must also perform many conversions very quickly in order to keep up with the continuous stream of video.

The computer must also be able to handle the audio conversion simultaneously. The smallest unit of audio is a called a sample. High-quality audio requires more samples per second, plus a computer that has the speed and memory to process the continuous stream.

To encode directly to a Windows Media file or broadcast stream from audio and video capture cards, you will typically use Windows Media Encoder. However, you can perform basic encoding tasks from the command line with Windows Media Encoding Script. In the optimal system, rather than capture and encode in one step, an AVI file is first captured with Windows Media Capture 9 Series utility. Then the final Windows Media Video file is encoded from the AVI file. This two-step method is often preferred for encoding high-bandwidth video, because it requires less processing power and memory, and therefore can help ensure a higher quality capture.

Considering Compression
The digital audio and video streams of samples and pixels are measured as the bit rate of the content, such as 700 kilobits per second (Kbps). High-quality professional video has a bit rate that far exceeds the capacity of most computers and networks: 270 megabits per second (Mbps). In order to work with digital media on a computer and stream it over a network, it must be compressed. The program that compresses and decompresses digital media is called a codec.

The Windows Media Audio 9 and Windows Media Video 9 codecs offer a great deal of user flexibility because they are highly scalable, which means you can choose the amount of compression and the bit rate for a wide variety of scenarios. For example, you can sacrifice some quality and compress to very low bit rates for streaming media at telephone modem speeds, or maintain high quality and high bit rates to stream or download over a high-bandwidth network or to save to a CD.

When designing your production workstation, you must consider the codec and bit rates you will use. Analog-to-digital conversion and the compression process require a great deal of processing power for high bit rate content. If you follow the recommendations for the optimal system, your workstation will be able to handle the workload and create high-quality content.

The Key to High Quality
There are two primary methods for encoding video:

* Capturing and encoding from a live stream directly to a Windows Media file as a real time process.
* Capturing to an uncompressed AVI file, and then encoding a Windows Media file from the AVI file in non-real time.


Real-time encoding is best used for live broadcasting, in which the primary stream is played back as it is being encoded. Real-time encoding requires a faster CPU and more random access memory (RAM). If the CPU can not keep up with the real time processing, it drops frames of video and motion can appear jerky.

Capturing to an AVI and then encoding in non-real time usually produces higher quality results. This method requires large amounts of hard disk space and faster system components (described in more detail later). However, the method does not require a fast CPU for encoding; complex encoding modes just take more time. By definition, the non-real time process is slower and requires more processing steps.

Except where noted, this article describes the system requirements for the non-real time encoding method.

The secret to capturing high-quality, high-bandwidth video is to use a computer system that can handle the bandwidth. A fast CPU with a large amount of RAM is helpful. However, a fast peripheral component interconnect (PCI) bus, fast hard disk with proper storage capacity, and a network connection that can handle the high bandwidth if you plan to stream to other computers is a requirement. Capture cards and external hardware should also be capable of producing high-quality images and sound. (For detailed recommendations, see the Hardware Recommendations section of this article.) There are several items you need to consider when building a high quality workstation:

* Source quality. The final product can be no better than the source. Make sure to use a high-quality, high-resolution videotape format, such as Digital Betacam or Mini-DV. With the proper digital interface, such as the IEEE 1394 (sometimes called FireWire) interface or the professional Serial Digital Interface (SDI), you can skip the analog-to-digital conversion that reduces quality. If you must convert from analog, make sure your video source is high quality. Use S-video connections, if available, and a professional-quality playback deck. Most of today's professional or semi-professional videotape decks are capable of producing suitable quality.

If you are capturing from a tuner, demodulator, film scanner, or router, make sure the cables and connections are professional quality and working properly, and the radio frequency (RF) connections to the tuner or demodulator are properly adjusted and terminated. Not only does poor source quality result in a poor quality product, any noise, glitches, or instability in the picture can increase the bit rate and size of the final file. The codec cannot distinguish detail in the video image from the detail in video noise, and attempts to reproduce the video imperfections just as faithfully as the rest of the image.

* Fast CPU, PCI bus, and a large hard drive and RAM. A fast CPU enables a computer to keep up with the demand imposed by the continuous stream of bits, while a fast PCI bus moves those bits easily between the capture device and the processor. A large amount of RAM eases the load on the CPU by enabling bits to be cached as they are converted. A large hard disk with a fast access time eases the load on the computer by writing data quickly and efficiently. As you capture data, you can use the System Monitor included with the Microsoft Windows® operating system to view CPU and memory usage. If the CPU percentage often hits 100 percent, there is a very good chance the capture quality will be impaired. If possible, use a computer with dual PCI buses. Even a very fast single PCI bus may not be able to handle both the bit stream produced by the capture card and the stream going to the hard disk drive.


* High-quality capture cards. A capture card is responsible for properly inputting and processing the audio and video signals, and then converting them into a digital stream of bits. For this reason, the video capture card is the most important link in the chain. A low-quality or outdated capture card can greatly reduce the quality of the video. After the video has been converted to digital form, the data can be stored, transferred, and copied without affecting quality.

High-Bandwidth Features of Windows Media

With Windows Media Audio 9 and Windows Media Video 9 codecs, you can achieve near-VHS quality at 250 Kbps and near-DVD quality at 750 Kbps with a variable bit rate (VBR) encoding mode. You can also improve the quality of high-bandwidth content by taking advantage of the following features:

* Deinterlacing. When encoding a video file captured at the full frame size of 640 x 480 pixels, the two interlaced fields contained in a single frame of NTSC video must be converted to one complete frame that can be displayed on a computer monitor. Computer monitors use a different method of displaying video called progressive scanning, which does not use interlaced fields. The deinterlacing feature converts interlaced video frames into progressively scanned frames, creating a cleaner, sharper image with fewer motion artifacts at both a full frame size and at 320 x 240 pixels.


* Inverse telecine. To convert film, which plays back at 24 frames per second (fps), to National Television System Committee (NTSC) standard video, which plays at 29.97 fps, a telecine, such as a film scanner, adds redundant fields to the video. When encoding video of a film, you can use the inverse telecine filter to remove those redundant fields and return the video to its original frame rate. The final encoded video appears more like the original film; and, with fewer frames, the file size is smaller and bit rate are lower. Inverse Telecine does not apply to Phase Alternate Line (PAL) video.


* 50 or 60 frames per second. You can create high-quality video that has very smooth and crisp motion by using the deinterlacing filter to encode from 640 x 480 pixels to 320 x 240 pixels, and then converting the video fields to frames. The 50 fields per second (PAL) or 60 fields per second (NTSC) are converted to 50 or 60 frames per second.


* Variable bit rate. Any on-screen movement results in an increase in the bit rate of a video, because new pixels must be generated from frame to frame. To stream over a network with Windows Media Services, you would use constant bit rate (CBR) encoding to constrain the bit rate to the available bandwidth. With CBR encoding, Windows Media Encoder keeps the bit rate below a specified level by dynamically reducing the quality of the video, or dropping frames if necessary. Playback is not always as smooth as one would like, but the end user experiences as smooth a presentation as possible for a given bandwidth.

For video that will not be streamed, you have the option of VBR encoding. VBR-encoded video cannot be streamed, but you can use it for content that is destined to be downloaded or played back locally or over a fast network. With VBR encoding, the integrity of high motion or rapid changes in the video is maintained by simply allowing the bit rate to vary as needed. You set the desired quality level, and the bit rate changes to maintain that quality.

* Two-pass CBR encoding. When using two-pass CBR encoding, content passes through the encoder twice. The first time, the encoder analyzes the complexity of the content. During the second pass, the analysis is used to encode the content. Two-pass CBR encoding produces a much cleaner and smoother video than the one-pass CBR method. Two-pass CBR encoding cannot be used with a broadcast stream.


* Two-pass VBR encoding. For two-pass VBR encoding, you specify a desired bit rate instead of a desired quality level. The encoder then adjusts the VBR quality level to create a file that is the equivalent size of a CBR file of the same specified bit rate. During the first pass, the encoder estimates what the final file size will be, and during the second pass it adjusts the quality level in order to create a file with the desired file size. Unlike two-pass CBR encoding, the data from the first pass is not used during the second pass.


* Nonsquare pixels. A pixel is the smallest unit of a digital image or frame. A resolution of 640 x 480 pixels produces a frame aspect of ratio 4:3 if the pixels are square. By using nonsquare pixels, which is supported in Windows Media, you can create any number of different aspect ratios and resolutions. For example, you can maintain the original resolution of digital video (720 x 480), which uses nonsquare pixels.


* Multiple bit rate (MBR) audio and video. You can encode one Windows Media file or stream that contains multiple streams encoded at different bit rates. MBR does not itself improve quality, but it enables you to provide the highest quality content for a wider variety user bandwidths. For example, in one MBR file you can support users connecting to the Internet with slow telephone modems, while providing high-quality content for users with broadband connections.


By using these features with the Windows Media Audio and Video codecs, you can create high-quality pictures and sound at a fraction of the file size and bit rate of conventional digital media. The typical computer display has a far higher resolution and faster frame rate than an analog television. This enables you to produce video with Windows Media that is higher quality than standard television. You can even encode high-bandwidth video that rivals the quality of film in a theater when using a digital cinema projector.

However, to do all this you need a system that can capture and maintain high quality.

Hardware Recommendations

The following section shows the recommended minimum and optimal hardware for capturing high-bandwidth content to an AVI file and encoding high-bandwidth Windows Media files from AVI files.

* Computer. A fast processor is useful, but not required for capturing video to an AVI file. Keep in mind, though, that the faster the computer is, the shorter the encoding time will be. A high-bandwidth, two-hour AVI file, for example, might take several hours to encode on a slow computer. More important than raw CPU clock speed is a fast front-side bus that will help transfer the video data to the hard disk without any conflicts or speed bottlenecks. For the latest information, see Windows Media Encoder 9 Series System Requirements.

Hard disk. To capture high-bandwidth content, your hard disk must be capable of a sustained access speed of 27 Mbps. Although many hard disks are rated with higher access speeds, they might not be capable of maintaining that speed throughout the capture of a two hour movie, which can result in dropped frames. It is recommended that you use Ultra160 small computer system interface (SCSI) drives with a RAID 0 striping. This configuration writes or stripes data across multiple hard disks, but appears as one drive on your desktop.

The SCSI disk array can be expensive. A less expensive alternative uses four integrated device electronics (IDE) drives with an IDE RAID controller board.

The size of the hard disk depends on how much content you plan to store. For example, if you plan to store a two-hour movie as an uncompressed AVI file, you will need 80 to 120 GB of space, depending on the resolution and pixel format that you capture to.

It is recommended that when you plan to build your production station, you shop around for the best solution at the time.

* Video capture card. Windows Media Encoder works with most capture devices that have Video for Windows or Windows Driver Model (WDM) drivers. To capture high quality, full-frame, and full-frame rate video to an AVI file, however, the list of capture cards narrows. Professional cards such as the Targa 3000 from Truevision, the Osprey 500 card from Viewcast, and the Reality Studio Digital Disk Recorder from DPS are well suited for high-quality video capture.

Some cards were created to capture content to be encoded to Windows Media Format. The Osprey-500 and Winnov Videum II, for example, handle much of the processing needs, so the computer's CPU and memory are free to compress and encode. The Osprey-500 also provides real-time deinterlacing and hardware-based digital video (DV) decoding for capturing MiniDV video. The cards can input video from a number of source types, such as MiniDV, SDI video and professional Digital Audio, or analog.

All of the cards that support video capture to a Windows Media file are listed on the Windows Media Hardware Product Vendors page at the Microsoft Web site. Keep in mind, however, that some of these cards may not produce the quality required to capture high-bandwidth video.

* Sound card. Many video cards also capture sound. In the optimal system, video and audio are captured digitally. Some cards are capable of capturing audio digitally or through an analog connection. Any high-quality sound card is suitable for capturing analog audio, but if you plan to capture audio digitally, make sure the card is capable of synchronizing to a digital source. Many cards also support multi-channel audio, such as 5.1 and 7.1 audio, which can be encoded directly to a Windows Media file or broadcast stream.


* Network card. You should design your workstation to be part of a network. Though files can be transferred to other computers with removable hard disks, it is far more efficient to connect the computers in a network. You can also connect the workstation through a proxy computer or firewall to the Internet, so that you can transfer files directly to your Web server or Windows Media server by using File Transfer Protocol (FTP). It is recommended that you use a fast network, such as an Ethernet 100BaseT system. The network cards and hub devices are inexpensive, and with the 100 Mbps data rate, you can copy large files quickly or play high-bandwidth files across the internal network. During the capture of an uncompressed AVI file, however, you should disable file sharing, or even disable the network completely, to eliminate the potential of external users accessing your system and hard disk.

Software Recommendations

The following section describes the basic software needed to capture AVI files and encode Windows Media files and broadcast streams. Your complete workstation may also include programs to edit video and design audio. You may also decide to install a packaged system that includes a capture card and editing system. If you do so, make sure the system is capable of capturing and editing full-frame video with no compression. In the optimal system outlined in this article, the highest quality is achieved by capturing data directly to the hard disk with no audio or video compression.

* Operating system. Windows Media Encoder 9 Series and the related encoder utilities can run on Microsoft Windows 2000 and Windows XP. It is recommended that you use the NTFS file system so that you can save files larger than 4 GB, which is the limit with FAT 32 file system. Before selecting an operating system, make sure your video capture card provides the appropriate driver. For example, some cards may only run on Windows 2000 Professional.


* Capture to AVI. You can use any program that enables you to capture full size (720 x 480 pixels for NTSC, 720 x 576 for PAL), full frame rate (29.97 or 25 frames per second), uncompressed video.

Depending on your capture card, you should capture to a YUY2 or YV12 pixel format. YUY2 produces a larger file, but provides more flexibility; YV12 produces a smaller file, but cannot be converted to other pixel formats as easily. YV12 may also be referred to as IYUV or I420. For more information, see The (Almost Definitive) FOURCC Definition List Leave this Web site.

The optimal system uses the simple Windows Media 9 Capture utility for capturing uncompressed AVI files with mono, stereo, 5.1, or 7.1 channels of audio, with up to 24 bit resolution and sampling rates up to 192kHz. You can download the utility from the encoder section of the Windows Media Download Center.

* Edit the AVI. There are a number of video editing and sound design programs, such as Adobe Premiere 6 and Sonic Foundry Vegas Video 4.0, with which you can work with full-frame uncompressed video. If you require no additional editing, you can simply encode the captured AVI file directly. For more information about these products, see the Sonic Foundry Leave this Web site and Adobe Leave this Web site Web sites.


* Capture and encode to Windows Media. Use Windows Media Encoder 9 Series, which you can download from the Windows Media Download Center. You can use Windows Media Encoder to capture directly to a Windows Media file or to a live stream for distribution to a Windows Media server for live broadcasting. You can also encode from an AVI file. You can also encode content with the Windows Media Encoding Script command line utility.