diff --git a/README.md b/README.md
index a10bb23..73446c5 100644
--- a/README.md
+++ b/README.md
@@ -45,7 +45,5 @@ Options:
 
 ## TODO
 
-* Fix alternate sort pattern features
-* Check for ffmpeg or avconv before executing
 * Generate example videos automatically
 * Publish example videos
\ No newline at end of file
diff --git a/frameloom b/frameloom
index 6e68bee..ad90cf6 100644
--- a/frameloom
+++ b/frameloom
@@ -219,6 +219,7 @@ async function weave(pattern, realtime, random) {
             alt = true;
     }
     if (random) {
+        log('Sorting frames randomly...');
         try {
             seq = await randomSort(frames, pattern, realtime);
         }
@@ -227,6 +228,7 @@ async function weave(pattern, realtime, random) {
         }
     }
     else if (!alt) {
+        log('Sorting frames normally...');
         try {
             seq = await standardSort(frames, pattern, realtime);
         }
@@ -235,8 +237,9 @@ async function weave(pattern, realtime, random) {
         }
     }
     else if (alt) {
-        log('This feature is not ready, please check https://github.com/sixteenmillimeter/frameloom.git', {});
-        process.exit(10);
+        //log('This feature is not ready, please check https://github.com/sixteenmillimeter/frameloom.git', {})
+        //process.exit(10)
+        log('Sorting frames with alternate pattern...');
         try {
             seq = await altSort(frames, pattern, realtime);
         }
@@ -256,34 +259,69 @@ async function weave(pattern, realtime, random) {
 async function altSort(list, pattern, realtime) {
     let groups = [];
     let newList = [];
+    let loops = 0;
+    let patternIndexes = [];
     let frameCount = 0;
+    let skipCount;
+    let skip;
+    let oldName;
     let oldPath;
     let newName;
     let newPath;
     let ext = path.extname(list[0]);
-    for (let g of pattern) {
+    let x;
+    let i;
+    for (x = 0; x < pattern.length; x++) {
         groups.push([]);
+        for (let i = 0; i < pattern[x]; i++) {
+            patternIndexes.push(x);
+        }
     }
-    for (let i = 0; i < list.length; i++) {
+    for (i = 0; i < list.length; i++) {
         groups[i % pattern.length].push(list[i]);
     }
-    for (let x = 0; x < list.length; x++) {
-        for (let g of pattern) {
-            for (let i = 0; i < g; i++) {
-                /*oldPath = path.join(TMPPATH, list[i]);
-                newName = `./render_${zeroPad(frameCount)}${ext}`;
-                newPath = path.join(TMPPATH, newName);
-
-                log(`Renaming ${list[i]} -> ${newName}`);
-
+    loops = Math.ceil(list.length / patternIndexes.length);
+    if (realtime) {
+        skip = false;
+        skipCount = patternIndexes.length + 1;
+    }
+    for (x = 0; x < loops; x++) {
+        for (i = 0; i < patternIndexes.length; i++) {
+            if (realtime) {
+                skipCount--;
+                if (skipCount === 0) {
+                    skip = !skip;
+                    skipCount = pattern.length;
+                }
+            }
+            if (typeof groups[patternIndexes[i]][0] === 'undefined') {
+                continue;
+            }
+            oldName = String(groups[patternIndexes[i]][0]);
+            oldPath = path.join(TMPPATH, oldName);
+            groups[patternIndexes[i]].shift();
+            if (skip) {
+                log(`Skipping ${oldName}`);
                 try {
-                    //await fs.move(oldPath, newPath, { overwrite: true })
-                    newList.push(newName);
-                } catch (err) {
-                    log(err);
-                }*/
+                    await fs.unlink(oldPath);
+                }
+                catch (err) {
+                    log('Error deleting frame', err);
+                }
+                continue;
+            }
+            newName = `./render_${zeroPad(frameCount)}${ext}`;
+            newPath = path.join(TMPPATH, newName);
+            log(`Renaming ${oldName} -> ${newName}`);
+            try {
+                await fs.move(oldPath, newPath);
+                newList.push(newName);
                 frameCount++;
             }
+            catch (err) {
+                log('Error renaming frame', err);
+                return process.exit(10);
+            }
         }
     }
     return newList;
@@ -483,6 +521,8 @@ async function main(arg) {
     let avconv = false;
     let random = false;
     let e = false;
+    let exe = arg.avconv ? 'avconv' : 'ffmpeg';
+    let exists;
     console.time('frameloom');
     if (input.length < 2) {
         log('Must provide more than 1 input', {});
@@ -518,6 +558,21 @@ async function main(arg) {
             pattern.push(1);
         }
     }
+    try {
+        exists = await exec(`which ${exe}`);
+    }
+    catch (err) {
+        log(`Error checking for ${exe}`);
+        process.exit(11);
+    }
+    if (!exists || exists === '' || exists.indexOf(exe) === -1) {
+        log(`${exe} is required and is not installed. Please install ${exe} to use frameloom.`);
+        process.exit(12);
+    }
+    if (pattern.length !== input.length) {
+        log(`Number of inputs (${input.length}) doesn't match the pattern length (${pattern.length})`);
+        process.exit(10);
+    }
     if (arg.realtime)
         realtime = true;
     TMPPATH = path.join(TMPDIR, 'frameloom');
@@ -538,7 +593,6 @@ async function main(arg) {
             return process.exit(4);
         }
     }
-    log('Weaving frames');
     try {
         await weave(pattern, realtime, random);
     }
diff --git a/package-lock.json b/package-lock.json
index 6352adb..4398406 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "frameloom",
-  "version": "1.0.2",
+  "version": "1.0.3",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
diff --git a/package.json b/package.json
index cf34dec..80dc685 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "frameloom",
-  "version": "1.0.2",
+  "version": "1.0.3",
   "description": "Node script to generate flicker videos by interweaving frames from multiple videos",
   "main": "frameloom",
   "scripts": {
diff --git a/src/frameloom.ts b/src/frameloom.ts
index db51713..25a0361 100755
--- a/src/frameloom.ts
+++ b/src/frameloom.ts
@@ -231,20 +231,23 @@ async function weave (pattern : number[], realtime : boolean, random : boolean)
 	}
 
 	if (random){
+		log('Sorting frames randomly...')
 		try {
 			seq = await randomSort(frames, pattern, realtime)
 		} catch (err) {
 			log('Error sorting frames', err)
 		}
 	} else if (!alt) {
+		log('Sorting frames normally...')
 		try {
 			seq = await standardSort(frames, pattern, realtime)
 		} catch (err) {
 			log('Error sorting frames', err)
 		}
 	} else if (alt) {
-		log('This feature is not ready, please check https://github.com/sixteenmillimeter/frameloom.git', {})
-		process.exit(10)
+		//log('This feature is not ready, please check https://github.com/sixteenmillimeter/frameloom.git', {})
+		//process.exit(10)
+		log('Sorting frames with alternate pattern...')
 		try {
 			seq = await altSort(frames, pattern, realtime)
 		} catch (err) {
@@ -263,39 +266,82 @@ async function weave (pattern : number[], realtime : boolean, random : boolean)
 async function altSort (list : string[], pattern : number[], realtime : boolean) {
 	let groups : any[] = []
 	let newList : string[] = []
+	let loops : number = 0
+	let patternIndexes : number[] = []
 	let frameCount : number = 0
+	let skipCount : number
+	let skip : boolean
+	let oldName : string
 	let oldPath : string
 	let newName : string
 	let newPath : string
 	let ext : string = path.extname(list[0])
+	let x : number
+	let i : number
 	
-	for (let g of pattern) {
+	for (x = 0; x < pattern.length; x++) {
 		groups.push([])
+		for (let i : number = 0; i < pattern[x]; i++) {
+			patternIndexes.push(x)
+		}
 	}
-	for (let i : number = 0; i < list.length; i++) {
+
+	for (i = 0; i < list.length; i++) {
 		groups[i % pattern.length].push(list[i])
 	}
-	for (let x : number = 0; x < list.length; x++) {
-		for (let g of pattern) {
-			for (let i : number = 0; i < g; i++) {
 
-				/*oldPath = path.join(TMPPATH, list[i]);
-				newName = `./render_${zeroPad(frameCount)}${ext}`;
-				newPath = path.join(TMPPATH, newName);
+	loops = Math.ceil(list.length / patternIndexes.length)
 
-				log(`Renaming ${list[i]} -> ${newName}`);
+	if (realtime) {
+		skip = false
+		skipCount = patternIndexes.length + 1
+	}
 
+	for (x = 0; x < loops; x++) {
+		for (i = 0; i < patternIndexes.length; i++) {
+
+			if (realtime) {
+				skipCount--;
+				if (skipCount === 0) {
+					skip = !skip;
+					skipCount = pattern.length
+				}
+			}
+
+			if (typeof groups[patternIndexes[i]][0] === 'undefined') {
+				continue
+			}
+
+			oldName = String(groups[patternIndexes[i]][0])
+			oldPath = path.join(TMPPATH, oldName)
+
+			groups[patternIndexes[i]].shift()
+
+			if (skip) {
+				log(`Skipping ${oldName}`)
 				try {
-					//await fs.move(oldPath, newPath, { overwrite: true })
-					newList.push(newName);
+					await fs.unlink(oldPath)
 				} catch (err) {
-					log(err);
-				}*/
+					log('Error deleting frame', err)
+				}
+				continue
+			}
 
+			newName = `./render_${zeroPad(frameCount)}${ext}`
+			newPath = path.join(TMPPATH, newName)
+			log(`Renaming ${oldName} -> ${newName}`)
+
+			try {
+				await fs.move(oldPath, newPath)
+				newList.push(newName)
 				frameCount++
+			} catch (err) {
+				log('Error renaming frame', err)
+				return process.exit(10)
 			}
 		}
 	}
+
 	return newList
 }
 /**
@@ -485,12 +531,6 @@ async function render (output : string, avconv : boolean) {
 	log(`Exporting video ${output}`)
 	log(cmd)
 
-	/*try {
-		await exec(`ls "${TMPPATH}"`)
-	} catch (err) {
-		log(err)
-	}*/
-
 	try {
 		await exec(cmd)
 	} catch (err) {
@@ -511,6 +551,8 @@ async function main (arg : any) {
 	let avconv : boolean = false
 	let random : boolean = false
 	let e  : any = false
+	let exe : string = arg.avconv ? 'avconv' : 'ffmpeg'
+	let exists : any 
 
 	console.time('frameloom')
 
@@ -555,6 +597,23 @@ async function main (arg : any) {
 		}
 	}
 
+	try {
+		exists = await exec(`which ${exe}`)
+	} catch (err) {
+		log(`Error checking for ${exe}`)
+		process.exit(11)
+	}
+
+	if (!exists || exists === '' || exists.indexOf(exe) === -1) {
+		log(`${exe} is required and is not installed. Please install ${exe} to use frameloom.`)
+		process.exit(12)
+	}
+
+	if (pattern.length !== input.length) {
+		log(`Number of inputs (${input.length}) doesn't match the pattern length (${pattern.length})`)
+		process.exit(10)
+	}
+
 	if (arg.realtime) realtime = true;
 
 	TMPPATH = path.join(TMPDIR, 'frameloom');
@@ -577,7 +636,6 @@ async function main (arg : any) {
 		}
 	}
 
-	log('Weaving frames')
 	try {
 		await weave(pattern, realtime, random)
 	} catch (err) {