[ffmpeg] Improve version check and call it from hls (Fixes #4377)

youtube_dl/downloader/hls.py

@@ -4,6 +4,7 @@ import os
 import re
 import subprocess
 
+from ..postprocessor.ffmpeg import FFmpegPostProcessor
 from .common import FileDownloader
 from ..utils import (
     compat_urlparse,
@@ -32,6 +33,9 @@ class HlsFD(FileDownloader):
             return False
         cmd = [program] + args
 
+        ffpp = FFmpegPostProcessor(downloader=self)
+        ffpp.check_version()
+
         retval = subprocess.call(cmd)
         if retval == 0:
             fsize = os.path.getsize(encodeFilename(tmpfilename))