diff --git a/src/tscut/exceptions.py b/src/tscut/exceptions.py
index 84c96b4..bad3b3e 100644
--- a/src/tscut/exceptions.py
+++ b/src/tscut/exceptions.py
@@ -18,5 +18,5 @@ class ExternalToolError(TSCutError):
 class InvalidMediaError(TSCutError):
     """Raised when input media cannot be processed."""
 
-class UnimplementedFeature(TSCutError):
+class UnimplementedFeatureError(TSCutError):
     """Raised when a rare feature is encountered and not yet implemented"""
diff --git a/src/tscut/h264/bitstream.py b/src/tscut/h264/bitstream.py
index 1f3f352..adca126 100644
--- a/src/tscut/h264/bitstream.py
+++ b/src/tscut/h264/bitstream.py
@@ -13,6 +13,7 @@ from math import floor, log
 from typeguard import typechecked
 import hexdump
 
+from tscut.exceptions import UnimplementedFeatureError
 
 logger = logging.getLogger(__name__)
 
@@ -284,7 +285,7 @@ def write_scaling_list(buf:bytearray, bit_position: int, size, matrix:list[int],
             bit_position = write_signed_exp_golomb(buf, bit_position, delta)
     else:
         logger.error('Not yet implemented')
-        raise UnimplementedFeature("Optimized scaling list of H264 header is not implemented")
+        raise UnimplementedFeatureError("Optimized scaling list of H264 header is not implemented")
         # reverse = deltas.reverse()
         # compressed = False
         # while len(reverse)>0:
diff --git a/src/tscut/tools/mkvtoolnix.py b/src/tscut/tools/mkvtoolnix.py
index f81eb20..277abf6 100644
--- a/src/tscut/tools/mkvtoolnix.py
+++ b/src/tscut/tools/mkvtoolnix.py
@@ -152,7 +152,7 @@ def change_codec_private_data(mkvinfo_path:str, input_file: IO[bytes], codec_dat
 
     if not found:
         logger.error('Impossible to retrieve the key of codec private data')
-        exit(-1)
+        raise InvalidMediaError("")
 
     if current_length < future_length:
         lseek(infd, position+current_data_length, SEEK_SET)