Fix crash if FFmpeg isn't found

`EncoderFFmpeg()` objects are now initialized while the program is
running, instead on invocation.

CHANGES.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 The release dates mentioned follow the format `DD-MM-YYYY`.
 
 ## [Unreleased]
+### Fixed
+- Failure on invoking spotdl if FFmpeg isn't found. It should now warn about missing
+  FFmpeg and move ahead without encoding. [@ritiek](https://github.com/ritiek)
+  (29b1f31a2622f749df83c3072c4cbb22615bff95)
 
 ## [2.0.3] (Hotfix Release) - 18-05-2020
 ### Fixed

spotdl/track.py

@@ -44,9 +44,9 @@ class Track:
         return progress_bar
 
     def download_while_re_encoding(self, stream, target_path, target_encoding=None,
-                                   encoder=EncoderFFmpeg(), show_progress=True):
+                                   encoder=EncoderFFmpeg, show_progress=True):
         total_chunks = self.calculate_total_chunks(stream["filesize"])
-        process = encoder.re_encode_from_stdin(
+        process = encoder().re_encode_from_stdin(
             stream["encoding"],
             target_path,
             target_encoding=target_encoding
@@ -80,10 +80,10 @@ class Track:
                 writer(response, progress_bar, file_io)
 
     def re_encode(self, input_path, target_path, target_encoding=None,
-                  encoder=EncoderFFmpeg(), show_progress=True):
+                  encoder=EncoderFFmpeg, show_progress=True):
         stream = self.metadata["streams"].getbest()
         total_chunks = self.calculate_total_chunks(stream["filesize"])
-        process = encoder.re_encode_from_stdin(
+        process = encoder().re_encode_from_stdin(
             stream["encoding"],
             target_path,
             target_encoding=target_encoding