[FFmpeg-trac] #9759(undetermined:new): Output always goes to stderr even when there are no errors.

[FFmpeg]

#9759: Output always goes to stderr even when there are no errors.
-------------------------------------+-------------------------------------
             Reporter:  Randall      |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:  stderr,      |               Blocked By:
  error output                       |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 In my code (written in Rust) I'm running an ffmpeg command and checking if
 stderr contains text.  But when I run a command successfully text is
 always output to stderr and nothing comes from stdout.  Other command line
 tools I've used behave normally with regards to stdout and stderr that my
 code uses, so this appears to be a problem with ffmpeg rather than Rust.

 How to reproduce:
   I run this command to combine a video and audio file:

 `ffmpeg -i 'bruh_video.mp4' -i 'bruh_audio.mp4' -c:v copy -c:a aac
 'bruh.mp4'`

  In Rust that code looks like

 ```
 let output =
         Command::new("sh")  //(Command is std::process::Command)
                 .arg("-c")
                 .arg(&format!("ffmpeg -i '{}' -i '{}' -c:v copy -c:a aac
 '{}'", video_filepath, audio_filepath, final_filepath))
                 .current_dir(&dl_folder)
                 .output()
                 .expect("failed to execute ffmpeg process");
     let stdout = String::from_utf8(output.stdout).unwrap();
     let stderr = String::from_utf8(output.stderr).unwrap();
 ```

 The stdout will be empty but stderr will contain all the normal output
 text.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9759>
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