Jennifer Winters
Microsoft New Media Platforms Division
November 2002
Introduction
Windows Media Encoder 9 Series is a powerful production tool for compressing audio and video content into a format that is suitable for streaming over the Internet, downloading onto users' computers, or playing back on hardware devices.
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Abstract
This document provides an overview of Microsoft® Windows Media® Encoder 9 Series, including basic steps involved in encoding and enhancements. Windows Media 9 Series codecs are discussed in detail. This document assumes that you have a basic understanding of audio and video concepts.
CBR and VBR Encoding Modes. Lists the encoding modes available with the encoder, including information about when each mode is appropriate for use.
Compressing Content. Provides information about the codecs included with the encoder.
For More Information. Lists other information sources you can pursue to learn more about using the encoder.
Steps Involved in Encoding
Using the encoder consists of three basic steps:
Choosing a source. You can encode live content in real time, audio or video files, or you can capture screens. Real-time sources include anything that you can plug into your audio or video card, including a CD player, microphone, VCR, video camera (both analog and digital), video tape recorder (VTR), video player, or NTSC television signals. You can also capture screens directly from your desktop, and insert script commands while encoding. The encoder supports sourcing from most common file types such as AVI and WAV.
The encoder works with most capture devices that have Windows Driver Model (WDM) drivers. New to this release is the ability to capture from ATI Radeon cards that support video capture. In addition, most USB cameras are supported.
Choosing your target destination and quality settings. Are you creating files for downloading? Do you plan to stream the content? Or are you creating a high-quality archive? The encoder includes many predefined destination, video, and audio settings that enable you to easily target your content for delivery to a variety of destinations, including set-top boxes, personal digital assistants (PDA), CD and DVD, and, of course, the Internet. You can also customize the default settings to meet your needs.
Selecting the distribution method. Encode content to a file or broadcast it live, either directly from the encoder or from a Windows Media server. Encoding to a file supports on-demand scenarios such as making music available for download from the Web, radio rebroadcasts, pay-per-view video, and video production and editing. A live broadcast enables streaming scenarios, such as Internet-based radio/TV stations, executive broadcasts, and live video distribution (point to point). Live broadcasts can be streamed directly from the encoder, or you can stream from a Windows Media server, using either push or pull distribution.
To simplify the steps above, the encoder includes quick starts and a New Session Wizard. Quick starts are session files included with the encoder that are designed to address common encoding scenarios; they already include most of the settings you need to begin encoding without delay. All you need to do is provide specifics about your content, such as file names or server names. You can also use the New Session Wizard, which walks you through the steps necessary to set up four of the most common encoding scenarios. This includes encoding a file, broadcasting a live event, capturing audio or video to file and performing a screen capture.
The encoder has evolved significantly over the past several years and now includes a rich set of features that give you more control and flexibility with unmatched audio and video quality.
New encoding modes. The encoder now includes support for one- and two-pass constant-bit-rate (CBR) and variable-bit-rate (VBR) encoding modes. See the topic "CBR and VBR Encoding Modes" in this document for more information.
Batch encoding. You can use Windows Media Encoding Script, a utility included with the encoder, to encode files by using the command line. You can automate the encoding of all your content at one time without having to configure the encoding session for each file. You can also encode all files in a folder.
Digital video camera and video tape recorder device control. You can directly control digital video (DV) cameras that are connected to an IEEE 1394 digital video port, or a video tape recorder (VTR) that supports the Sony RS422 protocol and that is connected through a COM port. You can also set up edit decision lists (EDLs), which specify discrete segments of your tape that you want to encode. This enables encoding to occur with minimal intervention on your part. Device control enables you to use one- or two-pass encoding when sourcing from DV cameras or VTRs.
Multichannel audio sourcing. Encode multichannel audio for surround sound playback in six (5.1 audio) or eight (7.1 audio) channels. The format is specifically designed for CD, DVD, high-definition television, and digital cinema audio programs. The channels are automatically folded down to two during playback with stereo speakers.
Live DRM. You can control the use of your encoded content by protecting it with digital rights management (DRM) technology while you are encoding. You can use DRM either when encoding to a file or when broadcasting the stream. Content is encoded, encrypted with a key, and then a license is required by users to play the content. This license contains the key to unlock the content and the rights that govern its use. For example, the license determines the number of times a user can play the content or when the license expires. Licenses are issued by a third-party license provider, so you must set up an account with one before you can protect your content; this step can be performed through the encoder.
Push distribution. Initiate a connection with a remote Windows Media server to stream content. This is useful if the encoder is behind a firewall or if you want more control from the encoder. You can create a publishing point from the encoder, and receive server-side statistics while streaming.
Interlace and nonsquare pixel support. Support for interlaced content enables you to get better playback on televisions. Nonsquare pixel support preserves the true resolution of DV and MPEG-2 content without distortion.
Improved multiple bit rate (MBR) streaming. Create the right file for any audience with MBR audio and video, and scalable video resolution for multiple frame sizes in a single stream.
Multiple languages. You can encode audio in different languages and then use Windows Media Stream Editor, a utility included with the encoder, to combine the languages into one Windows Media file. During playback, users can choose the language they want to listen to.
Additional features with encoder utilities. Four utilities are included to provide additional features. Use Windows Media Profile Editor to create and edit custom profiles; use Windows Media Stream Editor to split and combine streams in different files, and to add language support to a file; use Windows Media File Editor to index files, edit metadata, scripts, and markers in files, and to trim the start and end time of files after encoding; use the Windows Media Encoder Script for batch encoding.
Using Windows Media Encoder, you can encode audio and video content at either a constant bit rate (CBR) or a variable bit rate (VBR). The mode to use depends both on your source and on the scenario you are targeting.
One-pass CBR. Use when capturing live content, when broadcasting, or when you are targeting older players or devices. This mode provides a faster encoding time.
Two-pass CBR. Use when capturing from files and when encoding to a file. This mode provides high quality and can encode complex scenes.
Quality-based VBR (one-pass). Use when you want to ensure a constant quality level, for example when you are archiving content. Maintains consistent quality throughout; increases bit rate when necessary to maintain quality.
Bit rate-based VBR (two-pass). Use when you want to achieve the highest possible quality level while staying within a predictable average bandwidth. Use this mode when you are planning to create files that can be downloaded before being played, or when you want to control the size of the output file.
Peak bit rate-based VBR (two-pass). Use when you want to create content that will be played back on a device that has a constrained reading speed, such as a CD or DVD player. Similar to bit rate-based VBR encoding, except that you also specify the peak bit rate.
With one-pass encoding, the content passes through the encoder once, and compression is applied as the content is encountered. With two-pass encoding, the content is analyzed during the first pass, and then encoded in the second pass based on data gathered in the first pass. Two-pass encoding can result in better quality content, because the encoder can allocate the bits more effectively within the window specified by the buffer. However, two-pass encoding takes longer because the encoder goes through all of the content twice. Two-pass encoding is not available in all situations, such as when you are broadcasting a live event.
To enable streaming audio and video content, the content must be compressed to a reasonable size. The encoder accomplishes compression by applying algorithms to the data, taking into account the desired output quality and available bandwidth. Then, before the content is played, it is decompressed through the use of decompression algorithms. These compression and decompression algorithms are called codecs.
The following example illustrates the difference in size before and after compression. Before compression, a typical 2-hour TV movie would require 200 gigabytes (GB) to store on a computer, and about 225 megabits per second (Mbps) to stream. The streaming requirement is about 450 times the speed of a DSL connection, and about 4,000 times the speed of a 56 Kbps modem connection. On the other hand, after compression to VHS quality, the same movie would require approximately 0.5 GB of storage, and only about 500 kilobits per second (Kbps) to stream.
Codecs are designed with a particular type of content in mind. Because of this specialization, a codec rarely works efficiently for any type of media other than that for which it was designed. A codec that works well for music, for example, can produce good-quality speech, but probably will not compress the speech content to its absolute minimum size. For this reason, the encoder includes the codecs listed in the following table.
Codec
Description
Windows Media Audio 9
Provides a 20 percent improvement in compression over the Windows Media Audio 8 codec. Supports one- and two-pass CBR and VBR encoding. Capable of playback on Windows Media Player 6.4 and newer, and more than 120 Windows Media-compatible devices. (VBR content may have glitches or silence during playback in Windows Media Player version 6.4.)
Windows Media Audio 9 Professional
Enables a full surround sound experience on computers with installed multichannel audio cards and Microsoft Windows® XP. Captures full-resolution audio (24-bit/96-kHz sampling) in stereo, or 5.1 channel (or even 7.1) surround for streaming or download-and-play delivery at bit rates of 128 Kbps to 768 Kbps. Intelligently folds down multichannel audio to two channels (stereo) or one channel (mono), depending on the speaker configuration of the playback device. Supports one- and two-pass CBR and VBR encoding.
Windows Media Audio 9 Lossless
Provides mathematically lossless encoding of audio content (2 to 3:1 compression). Supports multichannel audio encoding and dynamic range control.
Windows Media Audio 9 Voice
Offers superior quality for audio content with a voice emphasis. Intended for playback at data rates below 20 Kbps. Enables mixed-mode encoding of voice and music. Intended for playback at bit rates at 20 Kbps or lower. Replaces the Sipro Labs ACELP codec.
Windows Media Video 9
Creates high-quality video for streaming, download-and-play, and physical format delivery scenarios. Provides a 15 to 50 percent improvement in compression over the Windows Media Video 8.1 codec, with the more significant improvement occurring at higher bit rates. Enables playback of interlaced content on televisions and set-top boxes. Supports resolutions ranging from 160120 pixels at 10 Kbps to 19201080 (1080i/p) at 3 to 20 Mbps. Supports one- and two-pass CBR and VBR encoding modes.
Windows Media Video 9 Screen
Provides improved handling of shaded images, screen motion, and scrolling for screen captures. Supports one-pass CBR and VBR encoding with no frame dropping. Fully optimized for both streaming and download-and-play scenarios.
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