diff --git a/facefusion/ffmpeg.py b/facefusion/ffmpeg.py
index d7f7c480..9aabaa61 100644
--- a/facefusion/ffmpeg.py
+++ b/facefusion/ffmpeg.py
@@ -69,8 +69,11 @@ def merge_video(target_path : str, output_video_resolution : str, output_video_f
 	temp_video_fps = restrict_video_fps(target_path, output_video_fps)
 	temp_file_path = get_temp_file_path(target_path)
 	temp_frames_pattern = get_temp_frames_pattern(target_path, '%08d')
-	commands = [ '-r', str(temp_video_fps), '-i', temp_frames_pattern, '-s', str(output_video_resolution), '-c:v', state_manager.get_item('output_video_encoder') ]
+	is_webm = filetype.guess_mime(target_path) == 'video/webm'
 
+	if is_webm:
+		state_manager.set_item('output_video_encoder', 'libvpx-vp9')
+	commands = [ '-r', str(temp_video_fps), '-i', temp_frames_pattern, '-s', str(output_video_resolution), '-c:v', state_manager.get_item('output_video_encoder') ]
 	if state_manager.get_item('output_video_encoder') in [ 'libx264', 'libx265' ]:
 		output_video_compression = round(51 - (state_manager.get_item('output_video_quality') * 0.51))
 		commands.extend([ '-crf', str(output_video_compression), '-preset', state_manager.get_item('output_video_preset') ])