Evaluating Media Quality for RealFlash Movies Flash

When you decide that you want to convert a Flash movie into a RealPlayer-compatible format, you will need to consider the audio quality and bandwidth that your target audience’s connection speed will require. This next section will explain how to properly set up the RealPlayer files for use on the Web.

Audio requirements
The most important RealPlayer authoring consideration within Flash movies is the use of audio. RealPlayer only supports Flash audio that uses Stream Sync mode. Event Synch audio cannot play in RealPlayer. Flash Stream audio needs to be set for raw compression that uses a sample rate of 11 kHz, 22 kHz, or 44 kHz.

Because the Real Encoder will be compressing the Flash sounds, we recommend that you begin your Real Flash movie production with uncompressed audio files. If you have imported .MP3 sound files into your Flash movies, the Real Encoder will recompress them for use in RealPlayer. Recompressed audio usually sounds worse than the original compressed audio. To set the output format of Flash Stream audio:

  1. Open the Publish Settings dialog (File➪Publish Settings).
  2. Select the Flash tab.
  3. Click the Set button next to the Audio Stream option.
  4. In the Sound Settings dialog , choose the Raw option in the Compression drop-down menu, and pick a Sample Rate that is appropriate for your Flash audio. If you are using Stereo Stream sounds, then do not check the Convert Stereo to Mono option let the Real Encoder merge the sound channels on export. Click OK.
  5. The Sound Settings dialog enables you to change the default compression used for Stream and Event Audio in Flash movies.

    The Sound Settings dialog enables you to change the default compression used for Stream and Event Audio in Flash movies.

  6. If you still have Event Sync audio in the Flash movie, you should prevent its export by clicking the Set button next to the Audio Event option and selecting Disable in its Compression drop-down menu.
  7. Finally, just in case you have given unique compression settings to Stream sounds in the Library, check the Override sound settings option in the Flash tab.

Bandwidth considerations
Because RealPlayer can stream two or more media tracks simultaneously, you need to watch the file sizes of all the tracks that will play in the RealPlayer. You need to decide how much bandwidth each media track (the Flash or the RealAudio track) will consume. In the RealPlayer tab for the Publish Settings dialog, you can select a bit rate for the tuned Flash .SWF file and choose an audio format for the RealAudio file. You must balance bandwidth usage between the tuned Flash file and RealAudio file based on the target audience settings.

SureStream and Single Rate RealMedia files
Before you can decide how to divide the bandwidth between Flash and RealAudio files, you need to know the difference between Singe Rate and SureStream as it applies to RealMedia. When you produce Real content, you need to know what kind of RealServer your Web provider (or server) has installed.

If you have access to RealServer G2 or RealServer 8, then you’ll be able to use SureStream files on your site. A SureStream file can be streamed at various bit rates, depending on the connection preferences of the user’s RealPlayer and the current network conditions. All SureStream files need to use RTSP (Real Time Streaming Protocol) instead of HTTP (Hypertext Transfer Protocol), the standard protocol for the Web. If you try to stream a SureStream file over HTTP, the lowest bit rate version that you selected for publish will stream to your users.

If you use an earlier RealServer and/or use HTTP to serve your Real files, then you can use Single Rate Real files that are published for specific connection speeds. With this method of distribution, you would create a separate Single Rate file for each connection speed that you want to support. Then, you would specify the source file for each connection speed in the SMIL document.

Determining bit rate
To select the proper bit rate for the tuned Flash file, subtract the bit rate of the RealAudio file from the total bit rate available for your target audience’s Internet connection speed. The formula to find the bit rate for the tuned Flash .SWF file is: Connection speed RealAudio bit rate = Flash .SWF bit rate

The average bit rate available for 56KB modem users is about 37 Kbps (in practical testing). A RealAudio file using the Music codec set for Single Rate streaming over a 56KB modem connection requires 20 Kbps. Therefore, the bit rate for the tuned Flash .SWF file should be around 17 Kbps: 37 Kbps – 20 Kbps = 17 Kbps The typical bandwidth available for target audiences is generally lower than the connection rate. Table lists the practical limits for each target audience.

Avarage connect speed of standard modem rates

Avarage connect speed of standard modem rates

If you choose to use SureStream RealAudio and multiple target audiences, we recommend that you use the bit rate of the lowest target audience to calculate the bit rate for the tuned Flash file. This ensures that all targeted connection speeds will be capable of playing the presentation with greater success.

Alternatively, you can create several individual combinations of tuned .SWF files and Single Rate RealAudio streams, using SMIL to deliver the appropriate files to each target audience. This method enables you to create larger (and higher quality) tuned .SWF files for faster connection speeds.

Real audio codecs and bit rates

Real audio codecs and bit rates



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