Support: Configuring the audio and video quality in AVChat 3
Audio/video quality profile files
In the installation folder of your video chat application you will find a folder named audio_video_quality_profiles. It contains several .xml files. We call these .xml files audio video quality profiles.
Each .xml file contains the settings used to encode the video/audio data that's coming from your computer webcam and microphone. To edit the .xml files use Notepad or any other text editor.
AVChat 3 ships with several such profile files that you can use out of the box.
Changing the audio/video quality profile used
To make AVChat 3 use another audio/video quality profile file for when users start broadcasting their web cam and microphone you need to change the value of the miccamsettingsurl variable inside avc_settings.php (or avc_settings.asp) to point to the .xml file of your choice.
The default audio/video profile is 256k_high_motion_low_picture_quality.xml. This profile will consume (for one stream) maximum 212kbits/s for video and 88 Kbits/s for audio, total: 256kbits/s.
Editing individual profile files (advanced)
Each of these files has the exact same XML structure. Each xml file contains 10 settings:
<item>
<nm>128 ISDN</nm>
<df>0</df>
<bytes>16000</bytes>
<q>0</q>
<fps>7</fps>
<kfps>28</kfps>
<w>200</w>
<h>150</h>
<snd>8</snd>
<sndSilencelevel>5</sndSilencelevel>
</item>
To make your own audio video quality profile, duplicate one of the existing xml files, give it a unique name and edit it with a text editor.
To use your own audio video quality profile upload it to your web server and point the miccamsettingsurl variable in the php/asp configuration file to it.
Each node/value pair explained:
Video settings
<bytes> This is the maximum amount of bytes that the video (not audio) can consume per second. If it is set to 0, the video stream from the user to the media server will consume as much bandwidth as possible to maintain the picture quality. Multiply by 8 to get the value in bits.
<q> This is the picture quality. If set to 0 it will use as much quality as possible, without exceeding the <bytes> value. Maximum is 100 but that will consume EXCESSIVE bandwidth. A value between 85-95 will produce really good picture quality!
<fps> This defines the video frame rate. 10, 15, 30 fps, etc... . Some web cams can only capture up to 15fps.
<kfps> Key frames. This tells AVChat3 that every <kfps> frames a full frame will be sent to the media server . The rest of the frames contain just the changes from the previous frame. By default you should set this to <fps>*4
<w> The width of the captured video in pixels
<h> The height of the captured video in pixels
Audio settings
<snd> The sound rate. Available values: 5,8,11,22,44. This directly affects the sound quality. The bigger the better. A sound rate of X will consume 2*X Kbits/s to send the audio. For example a sound rate of 11 will use 11*2 =22 Kbits/s while a sound rate of 44 will use 88Kbits/s.
<sndSilencelevel> Takes values from 0 to 100. Flash Player will consider any sound that is lower than the value of this tag as "silence" and thus will not send any data to the media server. Use 100 if you want to never send audio to the FMS server. Use 0 if you always want to send to the FMS server whatever the mic captures (even noise).
We recommend using 0 since if you use the default (10) Flash Player will stop broadcasting sound when you stop speaking. Even though this seems like a cool feature that cuts bandwidth in reality the listeners will frequently get the feeling that you've been cut off!
Misc settings
<nm> This is the name of the connection type. The value of this tag is not used in AVChat 3.
<df> If set to 1, this will be the connection type that will be used by default. The value of this tag is not used in AVChat 3.
More information:
You can specify the path to the .xml file to be used by the AVChat software inside the php/asp configuration file. This way you can keep several "bandwidth.xml" files and use one with higher quality video for "gold" users and one with lower quality video for "free" users.
There is an interesting article on the Macromedia web site regarding best practices for encoding live flash video. Click here to open it.
