ffmpeg: add -(no)stdin option.

Allows to disable interaction from standard input.
Useful, for example, if ffmpeg is in the background process group.
Roughly the same result can be achieved with "ffmpeg ... < /dev/null"
but it requires a shell.

Changelog

@@ -31,6 +31,7 @@ version next:
 - new option: -progress
 - 3GPP Timed Text decoder
 - GeoTIFF decoder support
+- ffmpeg -(no)stdin option
 
 
 version 0.11:

doc/ffmpeg.texi

@@ -361,6 +361,14 @@ the encoding process. It is made of "@var{key}=@var{value}" lines. @var{key}
 consists of only alphanumeric characters. The last key of a sequence of
 progress information is always "progress".
 
+@item -stdin
+Enable interaction on standard input. On by default unless standard input is
+used as an input.
+
+Useful, for example, if ffmpeg is in the background process group. Roughly
+the same result can be achieved with @code{ffmpeg ... < /dev/null} but it
+requires a shell.
+
 @item -debug_ts (@emph{global})
 Print timestamp information. It is off by default. This option is
 mostly useful for testing and debugging purposes, and the output

ffmpeg.c

@@ -5878,6 +5878,8 @@ static const OptionDef options[] = {
       "add timings for each task" },
     { "progress", HAS_ARG | OPT_EXPERT, {(void*)opt_progress},
       "write program-readable progress information", "url" },
+    { "stdin", OPT_BOOL | OPT_EXPERT, {(void*)&stdin_interaction},
+      "enable or disable interaction on standard input" },
     { "timelimit", HAS_ARG, {(void*)opt_timelimit}, "set max runtime in seconds", "limit" },
     { "dump", OPT_BOOL | OPT_EXPERT, {(void*)&do_pkt_dump},
       "dump each input packet" },