[EMAIL PROTECTED] wrote:
Hi All, I'm looking into resampling of audio and have few questions. Can somebody help me in understanding what are the capabilities of the Helix audio resampling ?Will audio system resample based on device's capabilities ? For E.g.. If a clip's sampling rate is 32KHz and if device does not support 32KHz, will the samples be resampled ? I noticed an array z_anValidSampleRates in hxaudsess.cpp. Are these the sampling rates supported ? I tried removing a sampling rate from this array and tried to play a clip of the same removed sampling rate, expecting the audio device to be opened on resampled rate, but audio device was opened on the clip's sample rate. And also the code on CHXAudioSession::GetDeviceFormat() (hxaudsess.cpp) creates a table of supported combination of sample rates and channels for the device. The tables first entry is always the clips exact properties except when "AudioDeviceSamplesPerSec" is added to the config file. When "AudioDeviceSamplesPerSec" is set on config file, the audio device is opened for the specified sampling rate rather than the clip's sampling rate. Where does the audio session check against the audio device properties (channels, sample rate) ? (Is there some validation done for mono, stereo property of the audio device and appropriate conversion ?)
You pretty much have it. The media engine will always try to open the audio device with the native properties of the clip being played. We never want to resample unless we have to. This is done, as you found out, by building a table of samplerate, channels, samplewidths combinations from the most desirable to the least. After that we simply loop through this table and call _CheckFormat() on each one. The first one that the audio code (audio/device/hxaudev.cpp) returns TRUE on we use. The media engine will then, if needed, resample everything to that frequency. If there are certain frequencies you don't want to use you can just check for them in hxuadev.cpp and return FALSE. We do this on some embedded platforms, for example, that only support a certain set of samplerates or channels. --greg
Thanks, Rajesh.
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