RTC Client API ACM Registry Settings (Windows CE 5.0)
The RTC Client API uses the registry to locate Audio Compression Manager (ACM) drivers that it can use to convert audio from one format to another.
For examples of the these registry settings, see RTC Client API ACM Sample Registry Configuration.
For more information about the codecs supported by RTC, including a comparison between native codecs and codecs provided by ACM drivers, see Codecs.
For general information about ACM, see Audio Compression Manager Drivers.
Each ACM driver to be used by RTC requires its own key beneath the HKEY_CURRENT_USER\Software\Microsoft\RTC\ACM registry key.
For example, an ACM driver implementing the G729 codec might have registry settings at the HKEY_CURRENT_USER\Software\Microsoft\RTC\ACM\G729 key.
The following table shows the registry values beneath each ACM driver key.
| Value : type | Description |
|---|---|
| Driver : REG_SZ | No default setting.
File name of the ACM driver that implements the codec. |
| PayloadType : REG_DWORD | No default setting.
Static payload type. If you want the RTC Client API to assign the value, set this value to 255. Dynamic payload types set here are treated as if they are static payload types. |
| CodecRank : REG_DWORD | No default setting.
An integer value between 0 and 100. The RTC Client API uses this value to select preferred codecs. Codecs with a CodecRank of 0 have the highest priority; codecs with a rank of 100 have the lowest. |
| FrameDuration : REG_DWORD | No default setting.
Time in milliseconds that corresponds to the wSamplesPerBlock parameter, explained in more detail in Samples per Block. |
Each ACM driver requires non-PCM wave format information in the HKEY_CURRENT_USER\Software\Microsoft\RTC\ACM\<codec name>\WaveFormat key.
For example, non-PCM wave format data for the G729 codec might be stored in the HKEY_CURRENT_USER\Software\Microsoft\RTC\ACM\G729\WaveFormat key.
The following table shows the registry values for this key.
| Value : type | Description |
|---|---|
| FormatTag : REG_DWORD | No default setting.
Waveform-audio format type. |
| Channels : REG_DWORD | No default setting.
Number of channels in the waveform-audio data. Monaural data uses one channel; stereo data uses two. |
| SamplesPerSec : REG_DWORD | No default setting.
Sample rate, in samples per second (hertz), at which each channel should be played or recorded. |
| AvgBytesPerSec : REG_DWORD | No default setting.
Required average data-transfer rate, in bytes per second, for the format. |
| BlockAlign : REG_DWORD | No default setting.
Block alignment, in bytes. The block alignment is the minimum atomic unit of data for the FormatTag format type. |
| BitsPerSample : REG_DWORD | No default setting.
Bits per sample. If FormatTag is WAVE_FORMAT_PCM, BitsPerSample should be 8 or 16. |
| bSize : REG_DWORD | No default setting.
This value corresponds to the cbSize member in the WAVEFORMATEX structure. This member is explained in more detail in Extra Bytes. |
You can also use the registry to specify a preferred codec, using the HKEY_CURRENT_USER\Software\Microsoft\RTC\Codec key.
The following table shows the registry values for this key.
| Value : type | Description |
|---|---|
| PreferredAudioCodec : REG_DWORD | No default setting.
Matches the PayLoadType of the codec to use. |
| UsePreferredCodec : REG_DWORD | No default setting.
If 1, use preferred codec. If 0, do not use preferred codec. |
See Also
RTC Client API Registry Settings | RTC Client API General Registry Settings
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