implemented check for ytdl & ffmpeg

coub-dl.py

@@ -1,4 +1,4 @@
-from subprocess import call, Popen, PIPE, check_output, DEVNULL
+from subprocess import call, Popen, PIPE, check_output, DEVNULL, CalledProcessError
 from os import listdir, remove
 from os.path import splitext, exists, join
 from re import match
@@ -138,6 +138,31 @@ def mux_streams(file_dict):
          stdout=DEVNULL, stderr=DEVNULL)
 
 
+@call_verbose(before_message='Checking your system for youtube-dl and ffmpeg... ', after_message='Found both!')
+def check_for_ytdl_and_ffmpeg():
+    error_str = '\nNo {} found in PATH! coub-dl requires youtube-dl & ffmpeg.'
+    ytdl_found = False
+    ffmpeg_found = False
+    try:
+        check_output(('youtube-dl', '--version'))
+        ytdl_found = True
+    except (CalledProcessError, FileNotFoundError):
+        pass
+    try:
+        check_output(('ffmpeg', '-version'))
+        ffmpeg_found = True
+    except (CalledProcessError, FileNotFoundError):
+        pass
+
+    if not ytdl_found and not ffmpeg_found:
+        print_opt(error_str.format('youtube-dl nor ffmpeg'))
+    elif not ytdl_found:
+        print_opt(error_str.format('youtube-dl'))
+    elif not ffmpeg_found:
+        print_opt(error_str.format('ffmpeg'))
+    exit()
+
+
 def determine_output_filename(url, user_supplied, extension, files_dict):
     if user_supplied is None:
         files_dict[File.OUTPUT] = check_output(('youtube-dl', '--get-title', url)).decode('utf-8').strip()
@@ -197,6 +222,8 @@ if __name__ == '__main__':
     args = parse_cmd_arguments()
     VERBOSE = False if args.nonverbose else True
 
+    check_for_ytdl_and_ffmpeg()
+
     # create dict that contains files used
     FILES = {Stream.AUDIO: 'audio', Stream.VIDEO: 'video',
              File.LIST: 'list.txt', File.LOOP: 'loop', File.FRACTION: 'fraction',