diff --git a/src/you_get/common.py b/src/you_get/common.py
index 03946bf3..1cb33dc3 100755
--- a/src/you_get/common.py
+++ b/src/you_get/common.py
@@ -499,6 +499,24 @@ class DummyProgressBar:
     def done(self):
         pass
 
+def get_output_filename(urls, title, ext, output_dir, merge):
+    merged_ext = ext
+    if (len(urls) > 1) and merge:
+        from .processor.ffmpeg import has_ffmpeg_installed
+        if ext in ['flv', 'f4v']:
+            if has_ffmpeg_installed():
+                merged_ext = 'mp4'
+            else:
+                merged_ext = 'flv'
+        elif ext == 'mp4':
+            merged_ext = 'mp4'
+        elif ext == 'ts':
+            if has_ffmpeg_installed():
+                merged_ext = 'mkv'
+            else:
+                merged_ext = 'ts'
+    return '%s.%s' % (title, merged_ext)
+
 def download_urls(urls, title, ext, total_size, output_dir='.', refer=None, merge=True, faker=False):
     assert urls
     if dry_run:
@@ -519,12 +537,12 @@ def download_urls(urls, title, ext, total_size, output_dir='.', refer=None, merg
             pass
 
     title = tr(get_filename(title))
+    output_filename = get_output_filename(urls, title, ext, output_dir, merge)
+    output_filepath = os.path.join(output_dir, output_filename)
 
-    filename = '%s.%s' % (title, ext)
-    filepath = os.path.join(output_dir, filename)
     if total_size:
-        if not force and os.path.exists(filepath) and os.path.getsize(filepath) >= total_size * 0.9:
-            print('Skipping %s: file already exists' % filepath)
+        if not force and os.path.exists(output_filepath) and os.path.getsize(output_filepath) >= total_size * 0.9:
+            print('Skipping %s: file already exists' % output_filepath)
             print()
             return
         bar = SimpleProgressBar(total_size, len(urls))
@@ -533,8 +551,8 @@ def download_urls(urls, title, ext, total_size, output_dir='.', refer=None, merg
 
     if len(urls) == 1:
         url = urls[0]
-        print('Downloading %s ...' % tr(filename))
-        url_save(url, filepath, bar, refer = refer, faker = faker)
+        print('Downloading %s ...' % tr(output_filename))
+        url_save(url, output_filepath, bar, refer = refer, faker = faker)
         bar.done()
     else:
         parts = []
@@ -556,10 +574,10 @@ def download_urls(urls, title, ext, total_size, output_dir='.', refer=None, merg
                 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'))
+                    ffmpeg_concat_flv_to_mp4(parts, output_filepath)
                 else:
                     from .processor.join_flv import concat_flv
-                    concat_flv(parts, os.path.join(output_dir, title + '.flv'))
+                    concat_flv(parts, output_filepath)
             except:
                 raise
             else:
@@ -571,10 +589,10 @@ def download_urls(urls, title, ext, total_size, output_dir='.', refer=None, merg
                 from .processor.ffmpeg import has_ffmpeg_installed
                 if has_ffmpeg_installed():
                     from .processor.ffmpeg import ffmpeg_concat_mp4_to_mp4
-                    ffmpeg_concat_mp4_to_mp4(parts, os.path.join(output_dir, title + '.mp4'))
+                    ffmpeg_concat_mp4_to_mp4(parts, output_filepath)
                 else:
                     from .processor.join_mp4 import concat_mp4
-                    concat_mp4(parts, os.path.join(output_dir, title + '.mp4'))
+                    concat_mp4(parts, output_filepath)
             except:
                 raise
             else:
@@ -586,10 +604,10 @@ def download_urls(urls, title, ext, total_size, output_dir='.', refer=None, merg
                 from .processor.ffmpeg import has_ffmpeg_installed
                 if has_ffmpeg_installed():
                     from .processor.ffmpeg import ffmpeg_concat_ts_to_mkv
-                    ffmpeg_concat_ts_to_mkv(parts, os.path.join(output_dir, title + '.mkv'))
+                    ffmpeg_concat_ts_to_mkv(parts, output_filepath)
                 else:
                     from .processor.join_ts import concat_ts
-                    concat_ts(parts, os.path.join(output_dir, title + '.ts'))
+                    concat_ts(parts, output_filepath)
             except:
                 raise
             else: