Fix ADTS parsing over multiple events

Simplify ADTS parsing algorith to assume it is invoked at the start of a sync sequence. Track progress through the ADTS data accrately so that subsequent events carrying frames after the first are parsed correclty.

@@ -434,19 +434,8 @@ AacStream = function() {
 
     buffer = packet.data;
 
-    // find ADTS frame sync sequences
-    // ADTS frames start with 12 byte-aligned ones
-    while (i < buffer.length) {
-      switch (buffer[i] & 0xf0) {
-      case 0xf0:
-        // skip past non-sync sequences
-        if (buffer[i - 1] !== 0xff) {
-          i++;
-          break;
-        }
-
-        // parse the ADTS header
-
+    // unpack any ADTS frames which have been fully received
+    while (i + 4 < buffer.length) {
       // frame length is a 13 bit integer starting 16 bits from the
       // end of the sync sequence
       frameLength = ((buffer[i + 2] & 0x03) << 11) |
@@ -463,16 +452,9 @@ AacStream = function() {
         data: buffer.subarray(i + 6, i + frameLength - 1)
       });
 
-        // move to one byte beyond the frame length to continue
-        // searching for sync sequences
-        i += frameLength;
-        break;
-      default:
-        // the top four bytes are not all ones so the end of the
-        // closest possible start sequence is at least two bytes ahead
-        i += 2;
-        break;
-      }
+      // flush the finished frame and try again
+      buffer = buffer.subarray(i + frameLength - 1);
+      i = 1;
     }
   };
 };

@@ -1007,6 +1007,40 @@ test('generates AAC frame events from ADTS bytes', function() {
   equal(frames[0].samplesize, 16, 'parsed samplesize');
 });
 
+test('parses across packets', function() {
+
+  var frames = [];
+  aacStream.on('data', function(frame) {
+    frames.push(frame);
+  });
+  aacStream.push({
+    type: 'audio',
+    data: new Uint8Array([
+      0xff, 0xf1,       // no CRC
+      0x10,             // AAC Main, 44.1KHz
+      0xbc, 0x01, 0x20, // 2 channels, frame length 9 bytes
+      0x00,             // one AAC per ADTS frame
+      0x12, 0x34        // AAC payload 1
+    ])
+  });
+  aacStream.push({
+    type: 'audio',
+    data: new Uint8Array([
+      0xff, 0xf1,       // no CRC
+      0x10,             // AAC Main, 44.1KHz
+      0xbc, 0x01, 0x20, // 2 channels, frame length 9 bytes
+      0x00,             // one AAC per ADTS frame
+      0x9a, 0xbc,       // AAC payload 2
+      0xde, 0xf0        // extra junk that should be ignored
+    ])
+  });
+
+  equal(frames.length, 2, 'parsed two frames');
+  deepEqual(frames[1].data,
+            new Uint8Array([0x9a, 0xbc]),
+            'extracted the second AAC frame');
+});
+
 // not handled: ADTS with CRC
 // ADTS with payload broken across push events