diff --git a/youtube_dl/downloader/__init__.py b/youtube_dl/downloader/__init__.py
index bb6afb1f8a..67c2840a58 100644
--- a/youtube_dl/downloader/__init__.py
+++ b/youtube_dl/downloader/__init__.py
@@ -31,13 +31,13 @@ def get_suitable_downloader(info_dict, params={}):
     protocol = determine_protocol(info_dict)
     info_dict['protocol'] = protocol
 
-    if (info_dict.get('start_time') or info_dict.get('end_time')) and FFmpegFD.supports(info_dict):
+    if (info_dict.get('start_time') or info_dict.get('end_time')) and FFmpegFD.available() and FFmpegFD.supports(info_dict):
         return FFmpegFD
 
     external_downloader = params.get('external_downloader')
     if external_downloader is not None:
         ed = get_external_downloader(external_downloader)
-        if ed.supports(info_dict):
+        if ed.available() and ed.supports(info_dict):
             return ed
 
     if protocol == 'm3u8' and params.get('hls_prefer_native'):
diff --git a/youtube_dl/downloader/external.py b/youtube_dl/downloader/external.py
index bb43677b76..edf85483ba 100644
--- a/youtube_dl/downloader/external.py
+++ b/youtube_dl/downloader/external.py
@@ -16,6 +16,7 @@
     encodeFilename,
     encodeArgument,
     handle_youtubedl_headers,
+    check_executable,
 )
 
 
@@ -50,6 +51,10 @@ def get_basename(cls):
     def exe(self):
         return self.params.get('external_downloader')
 
+    @classmethod
+    def available(cls):
+        return check_executable(cls.get_basename(), cls.available_opt)
+
     @classmethod
     def supports(cls, info_dict):
         return info_dict['protocol'] in ('http', 'https', 'ftp', 'ftps')
@@ -81,6 +86,8 @@ def _call_downloader(self, tmpfilename, info_dict):
 
 
 class CurlFD(ExternalFD):
+    available_opt = ['-V']
+
     def _make_cmd(self, tmpfilename, info_dict):
         cmd = [self.exe, '--location', '-o', tmpfilename]
         for key, val in info_dict['http_headers'].items():
@@ -94,6 +101,8 @@ def _make_cmd(self, tmpfilename, info_dict):
 
 
 class AxelFD(ExternalFD):
+    available_opt = ['-V']
+
     def _make_cmd(self, tmpfilename, info_dict):
         cmd = [self.exe, '-o', tmpfilename]
         for key, val in info_dict['http_headers'].items():
@@ -104,6 +113,8 @@ def _make_cmd(self, tmpfilename, info_dict):
 
 
 class WgetFD(ExternalFD):
+    available_opt = ['--version']
+
     def _make_cmd(self, tmpfilename, info_dict):
         cmd = [self.exe, '-O', tmpfilename, '-nv', '--no-cookies']
         for key, val in info_dict['http_headers'].items():
@@ -117,6 +128,8 @@ def _make_cmd(self, tmpfilename, info_dict):
 
 
 class Aria2cFD(ExternalFD):
+    available_opt = ['-v']
+
     def _make_cmd(self, tmpfilename, info_dict):
         cmd = [self.exe, '-c']
         cmd += self._configuration_args([
@@ -135,6 +148,10 @@ def _make_cmd(self, tmpfilename, info_dict):
 
 
 class HttpieFD(ExternalFD):
+    @classmethod
+    def available(cls):
+        return check_executable('http', ['--version'])
+
     def _make_cmd(self, tmpfilename, info_dict):
         cmd = ['http', '--download', '--output', tmpfilename, info_dict['url']]
         for key, val in info_dict['http_headers'].items():
@@ -147,6 +164,10 @@ class FFmpegFD(ExternalFD):
     def supports(cls, info_dict):
         return info_dict['protocol'] in ('http', 'https', 'ftp', 'ftps', 'm3u8', 'rtsp', 'rtmp', 'mms')
 
+    @classmethod
+    def available(cls):
+        return FFmpegPostProcessor().available
+
     def _call_downloader(self, tmpfilename, info_dict):
         url = info_dict['url']
         ffpp = FFmpegPostProcessor(downloader=self)