diff --git a/src/ffx/ffx.py b/src/ffx/ffx.py
index 59734a5..a7725e8 100755
--- a/src/ffx/ffx.py
+++ b/src/ffx/ffx.py
@@ -423,7 +423,7 @@ def convert(ctx,
     context['video_encoder'] = VideoEncoder.fromLabel(video_encoder)
 
     targetFormat = FfxController.DEFAULT_FILE_FORMAT
-    targetExtension  = FfxController.DEFAULT_FILE_EXTENSION
+    targetExtension  = 'mkv' if context['video_encoder'] == VideoEncoder.H264 else FfxController.DEFAULT_FILE_EXTENSION
 
     context['use_tmdb'] = not no_tmdb
     context['use_pattern'] = not no_pattern
@@ -757,8 +757,10 @@ def convert(ctx,
             for filterYield in chainIteration:
                 targetFilenameTokens += filterYield['suffices']
 
+
             targetFilename = f"{'_'.join(targetFilenameTokens)}.{sourceFilenameExtension if rename_only else targetExtension}"
 
+
             targetPath = os.path.join(output_directory, targetFilename) if output_directory else targetFilename
 
             ctx.obj['logger'].info(f"Creating file {targetFilename}")