optimize NAL unit parsing

use a state machine and byte read instead of word read and jump backwards in the array in case start code not found related to #162
mangui · Jul 1, 2015 · 9fbd025 · 9fbd025
1 parent 1115c04
commit 9fbd025
Showing 1 changed file with 58 additions and 51 deletions.
diff --git a/src/org/mangui/hls/demux/Nalu.as b/src/org/mangui/hls/demux/Nalu.as
@@ -24,62 +24,69 @@
 
         /** Return an array with NAL delimiter indexes. **/
         public static function getNALU(nalu : ByteArray, position : uint) : Vector.<VideoFrame> {
+            var len : uint = nalu.length,i : uint = position;
+            var unitHeader : int,lastUnitHeader : int = 0;
+            var unitStart : int,lastUnitStart : int = 0;
+            var unitType : int,lastUnitType : int = 0;
+            var audFound : Boolean = false;
+            var value : uint,state : uint = 0;
             var units : Vector.<VideoFrame> = new Vector.<VideoFrame>();
-            var unit_start : int;
-            var unit_type : int;
-            var unit_header : int;
-            var aud_found : Boolean = false;
             // Loop through data to find NAL startcodes.
-            var window : uint = 0;
-            nalu.position = position;
-            while (nalu.bytesAvailable > 4) {
-                window = nalu.readUnsignedInt();
-                // Match four-byte startcodes
-                if ((window & 0xFFFFFFFF) == 0x01) {
-                    // push previous NAL unit if new start delimiter found, dont push unit with type = 0
-                    if (unit_start && unit_type) {
-                        units.push(new VideoFrame(unit_header, nalu.position - 4 - unit_start, unit_start, unit_type));
-                    }
-                    unit_header = 4;
-                    unit_start = nalu.position;
-                    unit_type = nalu.readByte() & 0x1F;
-                    if(unit_type ==9) {
-                        aud_found = true;
-                    }
-                    /* if AUD already found and newly found unit is NDR or IDR,
-                        stop parsing here and consider that this IDR/NDR is the last NAL unit
-                        breaking the loop here is done for optimization purpose, as NAL parsing is time consuming ...
-                     */
-                    if (aud_found && (unit_type == 1 || unit_type == 5)) {
+            while (i < len) {
+                // finding 3 or 4-byte start codes (00 00 01 OR 00 00 00 01)
+                value = nalu[i++];
+                switch(state)
+                {
+                    case 0:
+                        if(!value) {
+                            state = 1;
+                            // unitHeader is NAL header offset
+                            unitHeader=i-1;
+                        }
                         break;
-                    }
-                    // Match three-byte startcodes
-                } else if ((window & 0xFFFFFF00) == 0x100) {
-                    // push previous NAL unit if new start delimiter found, dont push unit with type = 0
-                    if (unit_start && unit_type) {
-                        units.push(new VideoFrame(unit_header, nalu.position - 4 - unit_start, unit_start, unit_type));
-                    }
-                    nalu.position--;
-                    unit_header = 3;
-                    unit_start = nalu.position;
-                    unit_type = nalu.readByte() & 0x1F;
-                    if(unit_type ==9) {
-                        aud_found = true;
-                    }
-                    /* if AUD already found and newly found unit is NDR or IDR,
-                        stop parsing here and consider that this IDR/NDR is the last NAL unit
-                        breaking the loop here is done for optimization purpose, as NAL parsing is time consuming ...
-                     */
-                    if (aud_found && (unit_type == 1 || unit_type == 5)) {
+                    case 1:
+                        if(value) {
+                            state = 0;
+                        } else {
+                            state = 2;
+                        }
+                        break;
+                    case 2:
+                    case 3:
+                        if(value) {
+                            if(value === 1) {
+                                unitType = nalu[i] & 0x1f;
+                                if(unitType == 9) {
+                                    audFound = true;
+                                }
+                                if(lastUnitStart) {
+                                    // use Math.min(4,...) as max header size is 4.
+                                    // in case there are any leading zeros
+                                    // such as 00 00 00 00 00 00 01
+                                    //                  ^^
+                                    // we need to ignore them as they are part of previous NAL unit
+                                    units.push(new VideoFrame(Math.min(4,lastUnitStart-lastUnitHeader), i-state-1-lastUnitStart, lastUnitStart, lastUnitType));
+                                }
+                                lastUnitStart = i;
+                                lastUnitType = unitType;
+                                lastUnitHeader = unitHeader;
+                                if(audFound == true && (unitType === 1 || unitType === 5)) {
+                                  // OPTI !!! if AUD unit already parsed and if IDR/NDR unit, consider it is last NALu
+                                  i = len;
+                                }
+                            }
+                            state = 0;
+                        } else {
+                            state = 3;
+                        }
+                        break;
+                    default:
                         break;
-                    }
-                } else {
-                    nalu.position -= 3;
                 }
             }
-            // Append the last NAL to the array.
-            if (unit_start) {
-                units.push(new VideoFrame(unit_header, nalu.length - unit_start, unit_start, unit_type));
+            //push last unit
+            if(lastUnitStart) {
+                units.push(new VideoFrame(Math.min(4,lastUnitStart-lastUnitHeader), len-lastUnitStart, lastUnitStart, lastUnitType));
             }
             // Reset position and return results.
             CONFIG::LOGGING {
@@ -101,7 +108,7 @@
                     ];
                     if (units.length) {
                         var txt : String = "AVC: ";
-                        for (var i : int = 0; i < units.length; i++) {
+                        for (i = 0; i < units.length; i++) {
                             txt += NAMES[units[i].type] + ","; //+ ":" + units[i].length
                         }
                         Log.debug2(txt.substr(0,txt.length-1) + " slices");