diff --git a/src/you_get/common.py b/src/you_get/common.py
index 7c13066f..1a846b86 100644
--- a/src/you_get/common.py
+++ b/src/you_get/common.py
@@ -409,10 +409,20 @@ def download_urls(urls, title, ext, total_size, output_dir = '.', refer = None,
             print()
             return
         if ext == 'flv':
-            from .processor.join_flv import concat_flv
-            concat_flv(parts, os.path.join(output_dir, title + '.flv'))
-            for part in parts:
-                os.remove(part)
+            try:
+                from .processor.ffmpeg import has_ffmpeg_installed
+                if has_ffmpeg_installed():
+                    from .processor.ffmpeg import ffmpeg_concat_flv_to_mp4
+                    ffmpeg_concat_flv_to_mp4(parts, os.path.join(output_dir, title + '.mp4'))
+                else:
+                    from .processor.join_flv import concat_flv
+                    concat_flv(parts, os.path.join(output_dir, title + '.flv'))
+            except:
+                raise
+            else:
+                for part in parts:
+                    os.remove(part)
+            
         elif ext == 'mp4':
             try:
                 from .processor.join_mp4 import concat_mp4
@@ -428,6 +438,7 @@ def download_urls(urls, title, ext, total_size, output_dir = '.', refer = None,
                         os.remove(part)
                 else:
                     print('No ffmpeg is found. Merging aborted.')
+            
         else:
             print("Can't merge %s files" % ext)
     
diff --git a/src/you_get/processor/ffmpeg.py b/src/you_get/processor/ffmpeg.py
index f785bf96..4b5d1db7 100644
--- a/src/you_get/processor/ffmpeg.py
+++ b/src/you_get/processor/ffmpeg.py
@@ -60,3 +60,28 @@ def ffmpeg_concat_ts_to_mkv(files, output = 'output.mkv'):
             return False
     except:
         return False
+
+def ffmpeg_concat_flv_to_mp4(files, output = 'output.mp4'):
+    for file in files:
+        if os.path.isfile(file):
+            params = ['ffmpeg', '-i']
+            params.append(file)
+            params += ['-map', '0', '-c', 'copy', '-f', 'mpegts', '-bsf:v', 'h264_mp4toannexb']
+            params.append(file + '.ts')
+            
+            subprocess.call(params)
+    
+    params = ['ffmpeg', '-i']
+    params.append('concat:')
+    for file in files:
+        f = file + '.ts'
+        if os.path.isfile(f):
+            params[-1] += f + '|'
+    params += ['-c', 'copy', '-absf', 'aac_adtstoasc', output]
+    
+    if subprocess.call(params) == 0:
+        for file in files:
+            os.remove(file + '.ts')
+        return True
+    else:
+        raise