From b64d04c119cd835683b95c13667dbae5db8b939f Mon Sep 17 00:00:00 2001
From: Yen Chi Hsuan <yan12125@gmail.com>
Date: Sat, 22 Oct 2016 13:04:05 +0800
Subject: [PATCH] [utils] Clarify for redirecting STDIN  in get_exe_version()

---
 youtube_dl/utils.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/youtube_dl/utils.py b/youtube_dl/utils.py
index a89ff6908b..2770c5f1c5 100644
--- a/youtube_dl/utils.py
+++ b/youtube_dl/utils.py
@@ -1818,6 +1818,9 @@ def get_exe_version(exe, args=['--version'],
     """ Returns the version of the specified executable,
     or False if the executable is not present """
     try:
+        # STDIN should be redirected too. On UNIX-like systems, ffmpeg triggers
+        # SIGTTOU if youtube-dl is run in the background.
+        # See https://github.com/rg3/youtube-dl/issues/955#issuecomment-209789656
         out, _ = subprocess.Popen(
             [encodeArgument(exe)] + args,
             stdin=subprocess.PIPE,