Ability to mix longest buffer

README.md

@@ -22,7 +22,7 @@ Utility functions for [_AudioBuffers_](https://github.com/audiojs/audio-buffer)
 * [util.normalize(buf, dst?, start?, end?)](#utilnormalizebuffer-target-start0-end-0)
 * [util.removeStatic(buf, dst?, start?, end?)](#utilremovestaticbuffer-target-start0-end-0)
 * [util.trim(buf, lvl)](#utiltrimbuffer-threshold0)
-* [util.mix(a, b, amt?, off?)](#utilmixbuffera-bufferb-ratiovala-valb-i-channelval-offset0)
+* [util.mix(a, b, amt?, off?, longest?)](#utilmixbuffera-bufferb-ratiovala-valb-i-channelval-offset0)
 * [util.size(buf)](#utilsizebuffer)
 * [util.data(buf, dst?)](#utildatabuffer-data)
 
@@ -194,8 +194,8 @@ a.getChannelData(1) // [-.1, .1]
 
 Create buffer with trimmed zeros from the start and/or end, by the threshold amplitude.
 
-### `util.mix(bufferA, bufferB, ratio|(valA, valB, i, channel)=>val?, offset=0)`
-Mix second buffer into the first one. Pass optional weight value or mixing function.
+### `util.mix(bufferA, bufferB, ratio|(valA, valB, i, channel)=>val?, offset=0, longest=false)`
+Mix second buffer into the first one. Pass optional weight value or mixing function. If longest parameter is passed, function will keep mixing until the longest of either `(bufferA)` or `(offset + bufferB)` has finished. For example, if `bufferA.length = 10`, `offset = 5` and `bufferB.length = 7`, then the total length will be `12` since `(offset + bufferB.length)` overruns `bufferA.length` by `2`.
 
 ### `util.size(buffer)`
 Return buffer size, in bytes. Use [pretty-bytes](https://npmjs.org/package/pretty-bytes) package to format bytes to a string, if needed.

index.js

@@ -562,28 +562,67 @@ function trimInternal(buffer, level, trimLeft, trimRight) {
  * is reduced amount of calculations and flexibility.
  * If required, the cloning can be done before mixing, which will be the same.
  */
-function mix (bufferA, bufferB, ratio, offset) {
+function mix (bufferA, bufferB, ratio, offset, longest) {
 	validate(bufferA);
 	validate(bufferB);
 
+
 	if (ratio == null) ratio = 0.5;
 	var fn = ratio instanceof Function ? ratio : function (a, b) {
 		return a * (1 - ratio) + b * ratio;
 	};
 
 	if (offset == null) offset = 0;
 	else if (offset < 0) offset += bufferA.length;
+
+	if (longest) {
+		return mixLongest(bufferA, bufferB, fn, offset);
+	} else {
+		for (var channel = 0; channel < bufferA.numberOfChannels; channel++) {
+			var aData = bufferA.getChannelData(channel);
+			var bData = bufferB.getChannelData(channel);
+
+			for (var i = offset, j = 0; i < bufferA.length && j < bufferB.length; i++, j++) {
+				aData[i] = fn.call(bufferA, aData[i], bData[j], j, channel);
+			}
+		}
+
+		return bufferA;	
+	}
+}
+
+/**
+ * Mix as far as possible. This means to make the resulting buffer as large as
+ * the max of (offset + bufferB) or bufferA. So if offset + bufferB finishes
+ * after bufferA, keep mixing in bufferB after bufferA has finished. 
+ */
+function mixLongest(bufferA, bufferB, fn, offset) {
+	const newLen = Math.max(offset + bufferB.length, bufferA.length); 
+	var newBuf = create(newLen, bufferA.numberOfChannels, bufferA.sampleRate);
+
+	// Copy bufferA so we can start mixing at the offset later
+	copy(bufferA, newBuf);
 
 	for (var channel = 0; channel < bufferA.numberOfChannels; channel++) {
+		var newData = newBuf.getChannelData(channel);
 		var aData = bufferA.getChannelData(channel);
 		var bData = bufferB.getChannelData(channel);
 
-		for (var i = offset, j = 0; i < bufferA.length && j < bufferB.length; i++, j++) {
-			aData[i] = fn.call(bufferA, aData[i], bData[j], j, channel);
+		for (var i = 0; i < newLen; i++) {
+			var a = aData[i+offset] === undefined ? 0 : aData[i+offset];
+			var b = bData[i] === undefined ? 0 : bData[i];
+
+			if(a === 0) {
+				newData[i+offset] = b;
+			} else if (b === 0) {
+				newData[i+offset] = a;
+			} else {
+				newData[i+offset] = fn.call(bufferA, a, b, i, channel);
+			}
 		}
 	}
 
-	return bufferA;
+	return newBuf;
 }
 
 

test.js

@@ -607,6 +607,30 @@ test('mix', function (t) {
 	t.throws(function () {
 		util.mix([1,2,3], [4,5,6], 0.1);
 	});
+
+	// Offset mix
+	// Starting with normal mix to see normal result
+	var a = AudioBuffer(2, [1,1,1,1]);
+	var b = AudioBuffer(2, [0,0,0,0]);
+	util.mix(a, b, null);
+	t.deepEqual(a.getChannelData(0), [0.5,0.5])
+	t.deepEqual(a.getChannelData(1), [0.5,0.5])
+
+	// Mix in at offset one, i.e. keep a's data until index 2
+	var a = AudioBuffer(2, [1,1,1,1]);
+	var b = AudioBuffer(2, [0,0,0,0]);
+	util.mix(a, b, null,1);
+	t.deepEqual(a.getChannelData(0), [1,0.5])
+	t.deepEqual(a.getChannelData(1), [1,0.5])
+
+	// Mix with longest setting. Will keep b's data after
+	// a finishes with respect to offset
+	var a = AudioBuffer(2, [1,1,1,1]);
+	var b = AudioBuffer(2, [0,0,0,0,1,1,1,1]);
+	var newBuf = util.mix(a, b, null, 1, true);
+	t.deepEqual(newBuf.getChannelData(0), [1,1,0,0,0])
+	t.deepEqual(newBuf.getChannelData(1), [1,1,1,1,1])
+
 	t.end()
 });