Chapter 7: Choosing Audiences

This chapter lists the properties of the predefined audiences. This information will help you to choose which audiences to use when encoding a clip or broadcast with the graphical application, as described in "Choosing Audiences". You can also use audience files when encoding with the command-line application, which Chapter 14 explains. Appendix C describes the syntax of the audience files, which you can edit manually.

Understanding Audiences

A single audience defines a range of parameters used to encode a clip or broadcast. It defines the audio codecs, the video codec, the maximum frame rate, and the maximum streaming bandwidth, for example. You can use the same audience to encode a video clip or an audio-only clip.

Audio Encoding for Audiences

Each audience setting defines four possible audio codecs. RealProducer uses one of those codecs depending on the type of audio used as the input:

• For a voice-only audio clip, an audience uses a voice codec. If the input is stereo surround or 5.1 multichannel audio, however, it uses a stereo surround or multichannel music codec to preserve audio data in the extra channels. RealProducer uses this codec when the clip is audio-only and you select Voice as the audio mode.
• For a video with voice-only narration, an audience uses a voice, stereo surround, or multichannel codec as appropriate. Because a video clip uses the majority of its bandwidth for its visual track, RealProducer generally uses a lower-bandwidth audio codec than when it encodes an audio-only clip. RealProducer uses this codec with a video clip when you select Voice as the audio mode.
• For a music audio clip, an audience uses a mono music, stereo music, stereo surround, or 5.1 multichannel codec depending on the input and the streaming bandwidth. RealProducer uses this codec when the clip is audio-only and you select Music as the audio mode.
• For a video with music, an audience uses a mono music, stereo music, stereo surround, or 5.1 multichannel codec depending on the input. The chosen codec is generally geared for a lower streaming speed than with a music-only clip, though, to preserve bandwidth for the visual track. RealProducer uses this codec with a video clip when you select Music as the audio mode.

For More Information: The section "Setting Audio Parameters" explains how to set the Voice or Music audio mode through the graphical application. For the command-line application, you use the -am option, described in the section "Audio Mode (- am)". See "Media Profile" for information about how the stream context is set in a job file.

Note: The audio codecs partially determine which versions of RealPlayer can play your clip or broadcast. The tables in this chapter summarize player compatibility. For specific information on a codec-by-codec basis, refer to "RealAudio Codecs".

Video Encoding for Audiences

The audience defines a default video codec, which is RealVideo 10 for desktop streaming and download audiences, and RealVideo 8 for mobile device audiences. However, you can use RealVideo 8, 9, or 10 with any audience. To change the video codec choice, you can do one of the following:

• Edit the audience file manually as described in Appendix C.
• Override the codec default when encoding with the graphical-application, as described in "Selecting a RealVideo Codec".
• Override the codec default when encoding with the command-line application, as described in "Video Codec Override (-vco)".

Note: The video codec partially determines which versions of RealPlayer can play your clip or broadcast. The tables in this chapter summarize player compatibility. For specific information on a codec-by-codec basis, refer to "RealVideo Codecs".

Which Audiences Should I Use?

RealProducer provides a number of predefined audiences designed to fit a variety of streaming and downloading requirements. The following sections guide you to the appropriate set of audiences to use. As you explore the audience choices, keep two important points in mind:

• With variable bit rate (VBR) audiences, you can choose only one audience for each job. All audiences not marked as "VBR" are constant bit rate (CBR) templates. You can use multiple CBR audiences in a job.
• As described in "Creating and Editing Audiences", you can modify existing audiences or define your own audiences. Before doing this, however, verify that the predefined audiences do not meet your needs. You should also be familiar with the audio and video issues described in Chapter 4 and Chapter 5, respectively.

Streaming to Low Bandwidth (Modem) Audiences

The audiences described in "Low-Bandwidth Streaming Audiences" are designed to stream to low-bandwidth viewers, such as RealPlayer users connecting to the Internet through modems. Because these audiences are SureStream-compatible, you can encode several of them into a single clip. You can also add audiences from the set listed in "High-Bandwidth Streaming Audiences".

Creating Streaming or Downloadable Clips for Broadband Audiences

The audiences described in "High-Bandwidth Streaming Audiences" are designed for broadband streaming connections such as digital subscriber line (DSL) and cable modems. Like the audiences described in "Low-Bandwidth Streaming Audiences", these audiences are SureStream-compatible, so you can encode several of them into a single clip.

For a downloadable clip, a VBR audience is the best choice. You can use VBR audiences for high-bandwidth streaming clips, too. However, you can choose only a single audience for each clip or broadcast when you use an audience listed in one of the following sections:

• The audiences described in the section "Variable Bit Rate Download Audiences" create the most general-purpose clips. The audio will be encoded as mono or stereo, depending on the input.
• You can encode downloadable clips based on a quality metric by using the audiences listed in the section "Quality Download Audiences". These audiences also produce mono or stereo audio output.
• The audiences described in "Stereo Surround Audiences" encode high-quality downloadable clips that preserve stereo surround information in the audio input.
• Use the audiences listed in the section "Multichannel Audio Audiences" to create downloadable clips from input that includes discrete, multichannel audio.
• For faithful encoding of standard mono or stereo input in audio-only clips, use the lossless codec described in "Lossless Audio".

Streaming or Downloading to Mobile Devices

The audiences described in "Mobile Device Audiences" are tailored to the needs of mobile devices such as smartphones and personal digital assistants.

Low-Bandwidth Streaming Audiences

This set of audiences encodes audio or video for streaming to RealPlayer across low-bandwidth Internet and intranet connections. Because these audiences are SureStream-compatible, you can encode multiple audiences into a clip, as explained in "SureStream CBR Clips". That same clip can also contain one or more high-bandwidth audiences listed in the section "High- Bandwidth Streaming Audiences".

Substream Audiences

The low-bandwidth streaming audiences include three substreams. These substreams are specifically intended as backups for dial-up modem audiences in cases where available bandwidth declines:

• 12k Substream for 28k Dial-up
• 16k Substream for 28k Dial-up
• 26k Substream for 56k Dial-up

Primary Audiences

You can choose any of the following audiences for your primary streams, or as backup streams for other higher-bandwidth, primary audiences:

• 28k Dial-up
• 56k Dial-up
• 64k Single ISDN
• 128k Dual ISDN
• 150k LAN

12k Substream for 28k Dial-up

This audience is used as a substream for the 28k Dial-up audience. You can include it, along with the 16k Substream for 28k Dial-up, when encoding a SureStream clip for modem users.

16k Substream for 28k Dial-up

This audience is a substream for the 28k Dial-up audience. You can include it, along with the 12k Substream for 28k Dial-up, when encoding a SureStream clip for modem users.

26k Substream for 56k Dial-up

This is a substream for the 56k Dial-up audience.

28k Dial-up

The 28 Kbps dial-up audience is the primary audience for users connecting to the Internet on 28.8 Kbps modems.

56k Dial-up

The 56 Kbps dial-up audience is the primary audience for users connecting to the Internet on 56 Kbps modems. This audience setting encodes stereo music for an audio-only clip. Lower-bandwidth substreams, such as the 26k Substream for 56k Dial-up, encode all audio output as mono. So if a 56 Kbps modem user is listening to a stereo music clip, a drop in bandwidth causes a shift to mono music.

64k Single ISDN

This is the primary audience for single-line ISDN. Although DSL lines and cable modems are replacing ISDN use in many countries, this audience can act as a substream for higher-bandwidth encodings.

128k Dual ISDN

This is the primary audience for dual-line ISDN. Although DSL lines and cable modems are replacing ISDN use in many countries, this audience can act as a substream for higher-bandwidth encodings.

150k LAN

This audience is designed for a local area network (LAN) such as a corporate intranet. This is the lowest-speed audience that uses stereo music for video soundtracks, and that can encode more than 15 frames of video per second.

High-Bandwidth Streaming Audiences

This set of audiences encodes audio or video for streaming to RealPlayer across broadband Internet connections. Use any of the following audiences, or a combination of several audiences, to create general-purpose clips that stream at high bandwidths:

• 256k DSL or Cable
• 384k DSL or Cable
• 512k DSL or Cable
• 768k DSL or Cable

Note: Because these audiences are SureStream-compatible, you can also encode in the same clip the audiences listed under "Low-Bandwidth Streaming Audiences". A single clip for narrowband and broadband streams works well for audio-only clips. With video, however, you may want to use different width and height dimensions for low-speed and high-speed audiences. For more information, refer to "Video Capture".

Tip: Although you can also use these audiences when creating clips intended for download, the audiences described in the section "Variable Bit Rate Download Audiences" are better suited for this purpose.

256k DSL or Cable

This audience targets 256 Kbps DSL and cable modem users. This is typically the lowest speed at which these services are offered.

384k DSL or Cable

This audience targets 384 Kbps DSL and cable modem users. It provides the highest-quality, audio-only encoding for a general streaming audience. Higher-speed audiences improve the video and audio-with-video quality, but will have the same audio-only quality.

512k DSL or Cable

This audience targets 512 Kbps (one-half Megabit) DSL and cable modem users. The music-with-video quality is better than the 384k DSL or Cable audience, but the audio-only quality is the same.

768k DSL or Cable

This audience targets 768 Kbps (three-quarters Megabit) DSL and cable users. For audio-only encoding, the audio quality is the same as the 384k DSL or Cable audience. With video, the audio quality is the same as the 512k DSL or Cable audience.

Mobile Device Audiences

The mobile device audiences are designed for streaming media to smartphones that include RealOne Player (or later) for mobile devices, as well as for creating download clips for personal digital assistants such as Palm devices and Pocket PC. These audiences have two features meant to accommodate the slower processors on these devices:

• The maximum frame rate for these audiences is lower than the frame rate for other streaming and download audiences. Decoding a high frame rate is processor-intensive. A lower frame rate is therefore recommended for mobile devices.
• RealVideo 8 is the preferred codec. It requires less processor power for decompressing video than RealVideo 9 and RealVideo 10.

Warning! When you encode with the graphical application, you will override the RealVideo 8 codec selection if you do not change the job's default setting from RealVideo 10. See "Selecting a RealVideo Codec".

When encoding a destination, you can choose one of the following mobile device audiences:

• General Mobile Streaming Audience
• General Mobile Local Playback Audience
• Pocket PC Local Playback Audience

General Mobile Streaming Audience

This audience is designed for streaming audio or video to smartphones.

General Mobile Local Playback Audience

This general-purpose audience produces audio or video clips suitable for download to most mobile devices.

Pocket PC Local Playback Audience

This audience is suitable for audio or video clips downloaded to Pocket PC devices or any other mobile device with a higher-speed processor.

Variable Bit Rate Download Audiences

This set of audiences encodes downloadable clips. You can also encode streaming clips or broadcasts using these audiences, as long as you understand the streaming characteristics described in "Variable Bit Rate Video". For each job, you can choose one of the following VBR download templates:

• 350k Download (VBR)
• 450k Download (VBR)
• 750k Download (VBR)
• 1M Download (VBR)
• 2M Download (VBR)
• 5M Download (VBR)

Tip: If you are unsure about your network characteristics, stick with the audiences described in "High-Bandwidth Streaming Audiences". Those audiences encode video at a lower quality, but make more conservative assumptions about available bandwidth.

For More Information: You can also create downloadable clips according to a quality metric. The section "Quality Download Audiences" lists the audiences that you use for this type of encoding. If your audio input is not mono or stereo, you may want to use a stereo surround or multichannel audience as described in "Stereo Surround Audiences" and "Multichannel Audio Audiences".

350k Download (VBR)

This is the lowest-speed VBR download audience.

450k Download (VBR)

This audience offers improved music-with-video quality from the 350k Download (VBR) audience. Higher-speed audiences improve the video quality but not the audio quality.

750k Download (VBR)

This audience provides the same audio quality as the 450k Download (VBR) audience.

1M Download (VBR)

With this audience, audio quality is the same as with the 450k Download (VBR) and 750k Download (VBR) audiences.

2M Download (VBR)

This audience offers very high download quality for large video clips.

5M Download (VBR)

This audience provides very high-quality playback for large video clips.

Quality Download Audiences

The quality download audiences are similar to the VBR audiences described in "Variable Bit Rate Download Audiences". You can use them if you wish to maintain a certain visual quality level in large, downloadable video clips. Because these audiences do not define an average bit rate, they are not good choices for streaming. When encoding a destination, you can choose one of these VBR quality download templates:

• 70% Quality Download (VBR)
• 80% Quality Download (VBR)
• 90% Quality Download (VBR)
• 100% Quality Download (VBR)

For More Information: For background on the difference between VBR clips encoded for quality or bit rate, refer to "VBR Encoding Settings".

Note: All quality-based download audiences provide the same audio quality, so you will notice quality improvements among the templates only with video clips.

70% Quality Download (VBR)

This audience template attempts to maintain a 70% quality level compared to the input video. You may notice a small number of imperfections added by the encoding process.

80% Quality Download (VBR)

This audience improves on the 70% Quality Download (VBR) audience settings.

90% Quality Download (VBR)

This audience attempts to replicate the input video nearly perfectly, within the constraints set by the maximum bandwidth and the video dimensions.

100% Quality Download (VBR)

Choose this audience to replicate the input video as perfectly as possible, given the constraints set by the maximum bandwidth and the video dimensions.

Stereo Surround Audiences

The stereo surround audiences are similar to the VBR audiences described in "Variable Bit Rate Download Audiences". You can use them for downloadable or streaming clips. However, you should select one of the following stereo surround audiences only if your audio input is stereo surround:

• 350k Surround Stereo (VBR)
• 450k Surround Stereo (VBR)
• 750k Surround Stereo (VBR)
• 1M Surround Stereo (VBR)
• 2M Surround Stereo (VBR)

For More Information: For background, refer to "What is Stereo Surround?". If you plan to stream a clip encoded with one of these audiences, see "VBR Clips for Streaming and Broadcasting".

350k Surround Stereo (VBR)

This is the lowest-speed audience offering stereo surround encoding.

450k Surround Stereo (VBR)

This audience offers the same audio quality as the 350k Surround Stereo (VBR) audience.

750k Surround Stereo (VBR)

For audio-only clips, this audience provides the same sound quality as the 350k Surround Stereo (VBR) and 450k Surround Stereo (VBR) audiences. The audio quality for video clips is higher, however.

1M Surround Stereo (VBR)

This audience offers high fidelity downloads, with improved audio quality over the 750k Surround Stereo (VBR) audience.

2M Surround Stereo (VBR)

This audience offers very high fidelity downloads, with improved audio quality over the 1M Surround Stereo (VBR) audience.

Multichannel Audio Audiences

The multichannel audiences are similar to the VBR audiences described in "Variable Bit Rate Download Audiences". You can use them for downloadable or streaming clips. However, you should select one of the following multichannel audiences only if your audio input has discrete, multichannel audio that you wish to preserve:

• 350k Multichannel (VBR)
• 450k Multichannel (VBR)
• 750k Multichannel (VBR)
• 1M Multichannel (VBR)
• 2M Multichannel (VBR)
• 5M Multichannel (VBR)

For More Information: For background, refer to "What is Multichannel Audio?". If you plan to stream a clip encoded with a multichannel audience, refer to "VBR Clips for Streaming and Broadcasting".

350k Multichannel (VBR)

This is the lowest-speed audience that preserves multichannel audio data.

450k Multichannel (VBR)

The audio encoding rates for this audience are the same as the 350k Multichannel (VBR) audience. Its higher bandwidth improves video quality only.

750k Multichannel (VBR)

This audience offers improved audio and video quality over the 450k Multichannel (VBR) audience.

1M Multichannel (VBR)

The audience offers improved video quality over the 750k Multichannel (VBR) audience. For audio-only clips, however, the audio quality is the same.

2M Multichannel (VBR)

This audience provides the highest overall audio quality of the multichannel audiences.

5M Multichannel (VBR)

This audience offers very high fidelity downloads. The audio encoding quality is the same as the 2M Multichannel (VBR) audience. You will notice improvements in the visual quality only.

Lossless Audio

The lossless audio audience is intended primarily to encode audio-only clips in a lossless format, which the section "Lossless Audio Codec" describes. You can use it to encode lossless audio with a video clip as well. However, the amount of bandwidth given to the video's visual track can vary greatly depending on how much bandwidth is required to encode the audio losslessly.