Tricia Gill
Microsoft Digital Media Division

May 16, 2001

Summery: Encoding audio and video content for streaming or downloading to a portable device, such as a Microsoft Pocket PC, introduces unique challenges. This article discusses some of those challenges and gives instructions for adjusting encoding profiles as necessary to ensure that your content is encoded successfully. (7 printed pages)

Contents

Executive Summary
Introduction
System Requirements
Encoding Considerations
Things To Remember
For More Information

Executive Summary

Encoding audio and video content for the Web should always be centered around your target audience. Whether you are streaming audio and video to a cable, DSL, or dial-up modem or preparing file-based content that will be downloaded and played, the capabilities of the computers that play your content will greatly influence the encoding settings you use.

Fortunately, producing content on a personal computer with Microsoft® Windows Media™ Encoder is a fairly straightforward process, especially when you use a standard encoding profile to set your compression level, bit rate, and output video size.

However, encoding content for streaming or downloading to a portable device, such as a Microsoft Pocket PC, introduces unique challenges. This article discusses some of those challenges and gives instructions for adjusting encoding profiles as necessary to ensure your content is encoded successfully.

Introduction

The Microsoft Windows Media™ Technologies platform is designed to deliver audio and video content for streaming or download over most networks, including the Internet. Using Microsoft Windows Media™ Encoder and Microsoft Windows Media™ Services, you can compress and stream your audio and video content to Microsoft Windows Media™ Player on desktop computers everywhere. Windows Media Player for Pocket PC now enables you to carry your favorite music and videos in the palm of your hand—and receive streaming audio and video from the Internet. This article discusses the encoding technologies of the Windows Media platform and how you can use Windows Media Encoder to encode your audio and video content for Pocket PC.

If you are already familiar with Windows Media Encoder, you know how easy it is to encode content for streaming or downloading over a variety of connections, from broadband to dial-up modems. Fortunately, encoding for portable devices is just as easy as encoding for desktop computers. The process itself is the same. The only real difference is that you are delivering audio and video content to a device with a smaller screen and less horsepower than most desktop computers.

The secret to making your content play effectively on portable devices is using the right encoding profile. Three new profiles, designed specifically for Pocket PC are already available on the Web, and customization is easy.

If you have not used Windows Media Encoder, you can download it from the Windows Media Encoder page of the the Microsoft Web site. The encoder is free to licensed users of Microsoft Windows®.

The article is arranged as follows:

• System Requirements . Lists the system requirements for playing audio and video content on the Pocket PC.
• Encoding Considerations. Provides information about encoding profiles and codecs, and gives specific examples for customizing profiles for streaming and full-resolution video.
• Things To Remember. Includes additional information about codecs, video size, and Microsoft Windows Media™ Rights Manager.
• For More Information. Provides links to additional resources and related articles.

System Requirements

Before users can play the audio or video content you have encoded, their Pocket PCs must meet the following minimum requirements:

Encoding Considerations

During the encoding process, Windows Media Encoder takes live or file-based content and compresses it for Internet delivery. Live content is content that you capture from a camera or other device that is connected to your computer's capture card. File-based content includes audio files, such as files with a .wav or .mp3 file name extension, or video files, such as files with an .avi file name extension. During the compression phase, the content is converted to Microsoft Windows Media™ Format so it can be streamed from a Windows Media server and played in Windows Media Player.

Before the actual compression or conversion takes place, Windows Media Encoder uses the New Session Wizard to collect information about your content. Some of the information that the wizard collects includes:

• Your sources (such as file, capture card, or screen)
• Your expected output (such as file, broadcast, or both)
• The distribution method for your content (such as a Web server or Windows Media server)
• The encoding profile that you want to use

While all of this information is important, it is the encoding profile that has unique implications when encoding for Pocket PC.

Profiles

An encoding profile is a collection of settings that is applied to your content during the encoding process in order to achieve a desired result. Settings in the profile include the audio and video compressor/decompressors (codecs) to be used during encoding, output video size, audio sampling rate, target bit rate, and other information. A number of profiles are pre-installed with Windows Media Encoder. They have a .prx file name extension and are installed in drive letter:\Program Files\Windows Media Components\Encoder\Profiles.

Three profiles, designed specifically for encoding content for Pocket PC, are now available on the Windows Media Encoder page of the Microsoft Web site. You can download these profiles and use them to encode content for streaming or local playback. Each profile is targeted at a specific device. For example, the Video for Pocket PC – Compaq iPAQ (Color) profile is intended for use with the Compaq iPAQ 3600 series. The other two profiles support the Casio Cassiopeia E-125 and EM-500 and HP Jornada 540 series, respectively. Each profile has been optimized for the particular device's processor, display, and so on. You should use each profile only with the device for which it is intended.

For example, the Video for Pocket PC – Compaq iPAQ (Color) profile supports bit rates up to 225.2 kilobits per second (Kbps). It uses the Microsoft Windows Media™ Audio 8 and Microsoft Windows Media™ Video 7 codecs, encodes the audio at 32 Kbps and 22 kHz stereo, has an output video size of 208 X 160 pixels, and delivers video at 20 frames per second (fps).

If the settings in the three profiles do not suit your needs, you can create your own profiles using the Profile Manager feature in Windows Media Encoder. It is recommended that you base your new profiles on the Pocket PC profile that you already have installed. To launch Profile Manager from the main encoder window on your desktop computer, point to the Tools menu and click Manage Profiles. Select an existing profile and click Edit, or click New to walk through the Profile Manager wizard. Specific examples of profile customizations are described later.

For more information about creating custom profiles with Profile Manager, see Windows Media Encoder Help.

Note   Additional Pocket PC profiles will be available in Microsoft Windows XP for use with Windows Media Encoder.

Codecs

As mentioned earlier, codecs are part of the encoding profile. Codecs are used to compress and decompress audio or video data. Windows Media Audio and Windows Media Video are two codecs that are used to decrease the bit rate of digital media files so they can be delivered efficiently over a network. Windows Media Encoder uses these codecs to compress the data for streaming, while Microsoft Windows Media Player decompresses the data for playback.

While Windows Media Encoder supports a number of codecs, not all content encoded with those codecs will play well on the Pocket PC. When encoding your audio content, you should use the Windows Media Audio codec. When encoding video content, use Windows Media Video 7 codec or ISO MPEG-4 video codec version 1.0. If you have content that was encoded with the MPEG-4 version 3 codec, you can play it on your Pocket PC. Content encoded with earlier versions of that codec will not play on a Pocket PC, and you will have to re-encode it.

Encoding content at full-screen resolution

The screen size of a Pocket PC is 320 X 240 pixels. The encoding profiles that are currently available for Pocket PC specify an output size of 208 X 160 pixels because this resolution provides the best compromise for quality, frame rate, and bit rate. Also, this size ensures that the video will fit into the standard Player user interface or within any custom skin that may have been applied to the Player.

Pocket PCs do have the ability to play video at full-screen resolution, or 320 X 240 pixels. If this is what you want to do, you can change the output video size in your profile accordingly. Because changing to the bigger resolution requires more processing power from the Pocket PC, you will have to offset the change in one or more of the other settings in the profile. Use Profile Manager to make the following changes:

1. Change the output video size to 320 X 240 pixels.
2. Drop your frame rate to 15 fps. You will not be able to achieve anything higher at full resolution.
3. Encode a portion of your video and play it back to test the quality. If further adjustments are necessary, proceed to step 4.
4. Drop your audio format to 20 Kbps, 22 kHz stereo or mono.
5. Raise your key frame interval to 4 seconds per key frame (or more, depending on the content).

Full-screen resolution is not suitable for streaming to Pocket PC over 28.8 or 56 Kbps modems.

Encoding content for streaming

The biggest factor to consider when encoding content for streaming is how your users will connect to a network or the Internet to receive the stream. Ideally, they will connect over a wireless network, which enables them to receive content at data rates up to 1 megabit per second (Mbps). But it is more than likely that they will have a CDPD or other cellular modem or an analog modem, which means they'll receive content at rates only up to 19.2 Kbps.

If you are encoding content for the higher-end users, you can use the three encoding profiles for Pocket PC to encode your content normally. But if your users are connecting with a 28.8 or 56 Kbps modem, then you should use one of the standard profiles already available in Windows Media Encoder for 28.8 and 56 Kbps users. These profiles are not unique to Pocket PC but do have an output video size, frame rate, and bit rate that are appropriate for streaming content to portable devices over dial-up modems.

If your users have the CDPD or cellular modem, then you will only be able to stream audio to them. You will have to create a custom profile that uses the Windows Media Audio codec, but make sure that it uses a low bit rate, such as 9.6 Kbps or less. Although Windows Media Encoder contains several audio-only profiles, these profiles either use the ACELP codec, which is not supported by Windows Media Player for Pocket PC, or encode the content at a bit rate that is too high for cellular modem users.

Things To Remember

Here are some additional considerations when encoding content for Pocket PC:

• Use Windows Media Encoder 7 or 7.1. Both versions support the Pocket PC profiles and the Windows Media Audio and Windows Media Video codecs.
• Use the Windows Media Video 7 codec. Although Windows Media Video 8 codec is supported, its compression technology places high demands on your CPU and is not yet optimal for portable devices. You can use the Windows Media Video 7 codec in Windows Media Encoder 7 and Windows Media Encoder 7.1.
• When creating custom encoding profiles, set the output video size to 320 X 240 pixels or smaller. Using a larger output video size will cause the quality of your encoded video to degrade because the video will be clipped or manipulated in some way in order to fit into the smaller screen. For best results, use 208 X 160 pixels.
• Windows Media Rights Manager enables you to set restrictions on how encoded content will be used. You can create a license that allows, for example, the transfer of content from a desktop computer to Pocket PC. You can also specify the number of transfers that are allowed and an expiration date after which the content can no longer be transferred. Users cannot acquire a license directly by downloading content from a Web page to their Pocket PC. Rather, they must download the content to the desktop computer first in order to acquire the license and then move the content to the portable device.
• Although you can encode content for Pocket PC using the Microsoft Windows Media™ 8 Encoding Utility, it is not recommended. The encoding utility is designed to produce high-quality content for download-and-play. Most portable devices are not powerful enough or do not have an adequate network connection to accommodate the large files.

For More Information

• For information about Windows Media Encoder 7 or 7.1, see Windows Media Encoder Help.
• For information about Windows Media Player for Pocket PC, see Windows Media Player Help.
• For information about Windows Media Technologies, see the Windows Media Technologies page at the Microsoft Web site.

Related MSDN article:

An Introduction to Windows Media Encoder 7.1