Method GetFrame

src/audio_effects/Compressor.cpp:48–105

This method is required for all derived classes of EffectBase, and returns a modified openshot::Frame object

// This method is required for all derived classes of EffectBase, and returns a
// modified openshot::Frame object
std::shared_ptr<openshot::Frame> Compressor::GetFrame(std::shared_ptr<openshot::Frame> frame, int64_t frame_number)
{
	// Adding Compressor
	const int num_input_channels = frame->audio->getNumChannels();
	const int num_output_channels = frame->audio->getNumChannels();
	const int num_samples = frame->audio->getNumSamples();

	mixed_down_input.setSize(1, num_samples);
	inverse_sample_rate = 1.0f / frame->SampleRate();
	inverseE = 1.0f / M_E;

	if ((bool)bypass.GetValue(frame_number))
		return frame;

	mixed_down_input.clear();

	for (int channel = 0; channel < num_input_channels; ++channel)
		mixed_down_input.addFrom(0, 0, *frame->audio, channel, 0, num_samples, 1.0f / num_input_channels);

	for (int sample = 0; sample < num_samples; ++sample) {
		float T = threshold.GetValue(frame_number);
		float R = ratio.GetValue(frame_number);
		float alphaA = calculateAttackOrRelease(attack.GetValue(frame_number));
		float alphaR = calculateAttackOrRelease(release.GetValue(frame_number));
		float gain = makeup_gain.GetValue(frame_number);
		float input_squared = powf(mixed_down_input.getSample(0, sample), 2.0f);

		input_level = input_squared;

		xg = (input_level <= 1e-6f) ? -60.0f : 10.0f * log10f(input_level);

		if (xg < T)
			yg = xg;
		else
			yg = T + (xg - T) / R;

		xl = xg - yg;

		if (xl > yl_prev)
			yl = alphaA * yl_prev + (1.0f - alphaA) * xl;
		else
			yl = alphaR * yl_prev + (1.0f - alphaR) * xl;

		control = powf (10.0f, (gain - yl) * 0.05f);
		yl_prev = yl;

		for (int channel = 0; channel < num_input_channels; ++channel) {
			float new_value = frame->audio->getSample(channel, sample)*control;
			frame->audio->setSample(channel, sample, new_value);
		}
	}

	for (int channel = num_input_channels; channel < num_output_channels; ++channel)
		frame->audio->clear(channel, 0, num_samples);

	// return the modified frame
	return frame;
}