Fix audio only using the right channel for volume; close #342

src/mp2.js

 	this.D = new Float32Array(1024);
 	this.D.set(MP2.SYNTHESIS_WINDOW, 0);
 	this.D.set(MP2.SYNTHESIS_WINDOW, 512);
-	this.V = new Float32Array(1024);
+	this.V = [new Float32Array(1024), new Float32Array(1024)];
 	this.U = new Int32Array(32);
 	this.VPos = 0;
 
 				this.VPos = (this.VPos - 64) & 1023;
 
 				for (var ch = 0;  ch < 2; ch++) {
-					MP2.MatrixTransform(this.sample[ch], p, this.V, this.VPos);
+					MP2.MatrixTransform(this.sample[ch], p, this.V[ch], this.VPos);
 
 					// Build U, windowing, calculate output
 					JSMpeg.Fill(this.U, 0);
 					var vIndex = (this.VPos % 128) >> 1;
 					while (vIndex < 1024) {
 						for (var i = 0; i < 32; ++i) {
-							this.U[i] += this.D[dIndex++] * this.V[vIndex++];
+							this.U[i] += this.D[dIndex++] * this.V[ch][vIndex++];
 						}
 
 						vIndex += 128-32;
 					dIndex -= (512 - 32);
 					while (vIndex < 1024) {
 						for (var i = 0; i < 32; ++i) {
-							this.U[i] += this.D[dIndex++] * this.V[vIndex++];
+							this.U[i] += this.D[dIndex++] * this.V[ch][vIndex++];
 						}
 
 						vIndex += 128-32;

src/wasm/mp2.c

 	float channel_left[SAMPLES_PER_FRAME];
 	float channel_right[SAMPLES_PER_FRAME];
 	float D[1024];
-	float V[1024];
+	float V[2][1024];
 	int U[32];
 } mp2_decoder_t;
 
 				self->v_pos = (self->v_pos - 64) & 1023;
 
 				for (int ch = 0;  ch < 2; ch++) {
-					matrix_transform(self->sample[ch], p, self->V, self->v_pos);
+					matrix_transform(self->sample[ch], p, self->V[ch], self->v_pos);
 
 					// Build U, windowing, calculate output
 					memset(self->U, 0, sizeof(self->U));
 					int v_index = (self->v_pos % 128) >> 1;
 					while (v_index < 1024) {
 						for (int i = 0; i < 32; ++i) {
-							self->U[i] += self->D[d_index++] * self->V[v_index++];
+							self->U[i] += self->D[d_index++] * self->V[ch][v_index++];
 						}
 
 						v_index += 128-32;
 					d_index -= (512 - 32);
 					while (v_index < 1024) {
 						for (int i = 0; i < 32; ++i) {
-							self->U[i] += self->D[d_index++] * self->V[v_index++];
+							self->U[i] += self->D[d_index++] * self->V[ch][v_index++];
 						}
 
 						v_index += 128-32;