Re: [FFmpeg-devel] [PATCH] Add FAQs about running in background (rev 2)

[Jim DeLaHunt]

On 2017-11-22 08:54, Michael Niedermayer wrote:


On Wed, Nov 15, 2017 at 12:43:30AM -0800, Jim DeLaHunt wrote:

Add two FAQs about running FFmpeg in the background.
The first explains the use of the -nostdin option in
a straightforward way. Text revised based on review.

The second FAQ starts from a confusing error message,
and leads to the solution, use of the -nostdin option.
The purpose of the second FAQ is to attract web searches
from people having the problem, and offer them a solution.

Add an anchor to the Main Options section of the ffmpeg
documentation, so that the FAQs can link directly there.
---
  doc/faq.texi| 65 +
  doc/ffmpeg.texi |  1 +
  2 files changed, 66 insertions(+)

will apply

thanks

[...]
And there it is: 
. 
Thank you!


--Jim DeLaHunt, j...@jdlh.com http://blog.jdlh.com/ (http://jdlh.com/)
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Re: [FFmpeg-devel] [PATCH] Add FAQs about running in background (rev 2)

[Michael Niedermayer]

On Wed, Nov 15, 2017 at 12:43:30AM -0800, Jim DeLaHunt wrote:
> Add two FAQs about running FFmpeg in the background.
> The first explains the use of the -nostdin option in
> a straightforward way. Text revised based on review.
> 
> The second FAQ starts from a confusing error message,
> and leads to the solution, use of the -nostdin option.
> The purpose of the second FAQ is to attract web searches
> from people having the problem, and offer them a solution.
> 
> Add an anchor to the Main Options section of the ffmpeg
> documentation, so that the FAQs can link directly there.
> ---
>  doc/faq.texi| 65 
> +
>  doc/ffmpeg.texi |  1 +
>  2 files changed, 66 insertions(+)

will apply

thanks

[...]
-- 
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

You can kill me, but you cannot change the truth.


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Re: [FFmpeg-devel] [PATCH] Add FAQs about running in background (rev 2)

[Jim DeLaHunt]

Ping. This patch responds to review comments, and there have been no 
further comments for a week. Could someone commit it please?


Thanks,
  —Jim DeLaHunt


On 2017-11-15 00:43, Jim DeLaHunt wrote:

Add two FAQs about running FFmpeg in the background.
The first explains the use of the -nostdin option in
a straightforward way. Text revised based on review.

The second FAQ starts from a confusing error message,
and leads to the solution, use of the -nostdin option.
The purpose of the second FAQ is to attract web searches
from people having the problem, and offer them a solution.

Add an anchor to the Main Options section of the ffmpeg
documentation, so that the FAQs can link directly there.
---
  doc/faq.texi| 65 +
  doc/ffmpeg.texi |  1 +
  2 files changed, 66 insertions(+)

diff --git a/doc/faq.texi b/doc/faq.texi
index dcaf89c6d2..73624c647e 100644
--- a/doc/faq.texi
+++ b/doc/faq.texi
@@ -501,6 +501,71 @@ ffmpeg -i ega_screen.nut -vf setdar=4/3 
ega_screen_anamorphic.nut
  ffmpeg -i ega_screen.nut -aspect 4/3 -c copy ega_screen_overridden.nut
  @end example
  
+@anchor{background task}

+@section How do I run ffmpeg as a background task?
+
+ffmpeg normally checks the console input, for entries like "q" to stop
+and "?" to give help, while performing operations. ffmpeg does not have a way 
of
+detecting when it is running as a background task.
+When it checks the console input, that can cause the process running ffmpeg
+in the background to suspend.
+
+To prevent those input checks, allowing ffmpeg to run as a background task,
+use the @url{ffmpeg.html#stdin-option, @code{-nostdin} option}
+in the ffmpeg invocation. This is effective whether you run ffmpeg in a shell
+or invoke ffmpeg in its own process via an operating system API.
+
+As an alternative, when you are running ffmpeg in a shell, you can redirect
+standard input to @code{/dev/null} (on Linux and Mac OS)
+or @code{NUL} (on Windows). You can do this redirect either
+on the ffmpeg invocation, or from a shell script which calls ffmpeg.
+
+For example:
+
+@example
+ffmpeg -nostdin -i INPUT OUTPUT
+@end example
+
+or (on Linux, Mac OS, and other UNIX-like shells):
+
+@example
+ffmpeg -i INPUT OUTPUT  ~/tmp/log.txt &
+[1] 93352
+%
+[1]  + suspended (tty output)  ffmpeg -i INPUT OUTPUT &>
+@end example
+
+The message "tty output" notwithstanding, the problem here is that
+ffmpeg normally checks the console input when it runs. The operating system
+detects this, and suspends the process until you can bring it to the
+foreground and attend to it.
+
+The solution is to use the right techniques to tell ffmpeg not to consult
+console input. You can use the
+@url{ffmpeg.html#stdin-option, @code{-nostdin} option},
+or redirect standard input with @code{< /dev/null}.
+See FAQ
+@ref{background task, @emph{How do I run ffmpeg as a background task?}}
+for details.
+
  @chapter Development
  
  @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?

diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index 7db80ebf6a..2bcad75973 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
@@ -470,6 +470,7 @@ 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".
  
+@anchor{stdin option}

  @item -stdin
  Enable interaction on standard input. On by default unless standard input is
  used as an input. To explicitly disable interaction you need to specify


--
--Jim DeLaHunt, j...@jdlh.com http://blog.jdlh.com/ (http://jdlh.com/)
  multilingual websites consultant

  355-1027 Davie St, Vancouver BC V6E 4L2, Canada
 Canada mobile +1-604-376-8953

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