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GUACAMOLE-25: Use linear interpolation for resampling input audio.

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Michael Jumper
2016-04-29 17:33:05 -07:00
parent cc9af8ed25
commit b36a955d20
1 changed files with 38 additions and 6 deletions
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44
guacamole-common-js/src/main/webapp/modules/AudioRecorder.js
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@@ -183,6 +183,43 @@ Guacamole.RawAudioRecorder = function RawAudioRecorder(stream, mimetype) {
*/
var maxSampleValue = (format.bytesPerSample === 1) ? 128 : 32768;
/**
* Determines the value of the waveform represented by the audio data at
* the given location. If the value cannot be determined exactly as it does
* not correspond to an exact sample within the audio data, the value will
* be derived through interpolating nearby samples.
*
* @param {Float32Array} audioData
* An array of audio data, as returned by AudioBuffer.getChannelData().
*
* @param {Number} t
* The relative location within the waveform from which the value
* should be retrieved, represented as a floating point number between
* 0 and 1 inclusive, where 0 represents the earliest point in time and
* 1 represents the latest.
*
* @returns {Number}
* The value of the waveform at the given location.
*/
var interpolateSample = function getValueAt(audioData, t) {
// Convert [0, 1] range to [0, audioData.length - 1]
var index = (audioData.length - 1) * t;
// Get the closest whole integer samples indices
var left = Math.floor(index);
var right = Math.ceil(index);
// Pull the values of the closest samples
var leftValue = audioData[left];
var rightValue = audioData[right];
// Determine the value of the sample at the given non-integer location
// through linear interpolation of the nearest samples
return leftValue + (rightValue - leftValue) / (right - left) * (index - left);
};
/**
* Converts the given AudioBuffer into an audio packet, ready for streaming
* along the underlying output stream. Unlike the raw audio packets used by
@@ -215,13 +252,8 @@ Guacamole.RawAudioRecorder = function RawAudioRecorder(stream, mimetype) {
// Fill array with data from audio buffer channel
var offset = channel;
for (var i = 0; i < outSamples; i++) {
// Apply naiive resampling
var inOffset = Math.floor(i / outSamples * inSamples);
data[offset] = Math.floor(audioData[inOffset] * maxSampleValue);
data[offset] = interpolateSample(audioData, i / (outSamples - 1)) * maxSampleValue;
offset += format.channels;
}
}