# Trouble capturing output of spawned process **URL:** \ **Category:** Ruby\ **Created:** [March 13, 2008, 2:32am UTC](https://www.ruby-forum.com/t/trouble-capturing-output-of-spawned-process/131764 "2008-03-13T02:32:56Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![snowbird122](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c68b51/32.png) [@snowbird122](https://www.ruby-forum.com/u/snowbird122)\ **Post date:** [March 13, 2008, 2:32am UTC](https://www.ruby-forum.com/t/trouble-capturing-output-of-spawned-process/131764/1 "2008-03-13T02:32:56Z")
Hello- I’m using the backtick notation to drive FFmpeg from Ruby. When FFmpeg runs, it outputs a fair amount of informational text to the console. I’m unable to read that data from my script. Here is my code: result = `ffmpeg -i test.avi -f flv -acodec mp3 output.flv` puts “HERE IS THE RESULT\n” puts result puts “\nRESULT COMPLETE” Here is the result when I run it: FFmpeg version SVN-rUNKNOWN, Copyright © 2000-2007 Fabrice Bellard, et al. configuration: --enable-gpl --enable-pp --enable-swscaler –enable-pthreads --enable-libvorbis --enable-libtheora --enable-libogg –enable-libgsm --enable-dc1394 --disable-debug --enable-shared –prefix=/usr libavutil version: 1d.49.3.0 libavcodec version: 1d.51.38.0 libavformat version: 1d.51.10.0 built on Jun 3 2007 20:59:25, gcc: 4.1.3 20070528 (prerelease) (Ubuntu 4.1.2-9ubuntu2) Input #0, avi, from ‘test.avi’: Duration: 00:00:01.8, start: 0.000000, bitrate: 6571 kb/s Stream #0.0: Video: cinepak, yuv420p, 640x480, 25.00 fps® Output #0, flv, to ‘output.flv’: Stream #0.0: Video: flv, yuv420p, 640x480, q=2-31, 200 kb/s, 25.00 fps© Stream mapping: Stream #0.0 -\> #0.0 Press [q] to stop encoding frame= 45 q=31.0 Lsize= 436kB time=1.8 bitrate=1985.8kbits/s video:435kB audio:0kB global headers:0kB muxing overhead 0.203409% HERE IS THE RESULT RESULT COMPLETE I was expecting the output to be bracketed by the text “HERE IS THE RESULT” and “RESULT COMPLETE”, but it looks like the infomation isn’t being put into the variable. I’m running this using Ruby 1.8.6 on Ubuntu 7.10. I’m connecting to the machine using PuTTY from my Windows XP machine. Does anyone know what might be going on? Regards- Eric ---
**Author:** ![snowbird122](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c68b51/32.png) [@snowbird122](https://www.ruby-forum.com/u/snowbird122)\ **Post date:** [March 13, 2008, 3:08am UTC](https://www.ruby-forum.com/t/trouble-capturing-output-of-spawned-process/131764/2 "2008-03-13T03:08:59Z")
Eric M. wrote: > I was expecting the output to be bracketed by the text “HERE IS THE > RESULT” and “RESULT COMPLETE”, but it looks like the infomation isn’t > being put into the variable. It may not be doing what you think it is. You may find that the output from ffmpeg is going directly to stderr. Inspect result to see if it contains anything, and if not then try result=`ffmpeg -i test.avi -f flv -acodec mp3 output.flv 2>&1` to see if that does the trick. ---
**Author:** ![snowbird122](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c68b51/32.png) [@snowbird122](https://www.ruby-forum.com/u/snowbird122)\ **Post date:** [March 13, 2008, 3:28am UTC](https://www.ruby-forum.com/t/trouble-capturing-output-of-spawned-process/131764/3 "2008-03-13T03:28:08Z")
Hi Paul- Thanks for your reply. I inspected the variable result and it is an empty string. I tried the syntax that you recommended, but it caused that commnd to hang. What is the “2\>&1” supposed to do? Does that pipe stderr into stdout? Regards- Eric ---
**Author:** ![snowbird122](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c68b51/32.png) [@snowbird122](https://www.ruby-forum.com/u/snowbird122)\ **Post date:** [March 13, 2008, 11:15am UTC](https://www.ruby-forum.com/t/trouble-capturing-output-of-spawned-process/131764/4 "2008-03-13T11:15:33Z")
Eric M. wrote: > that commnd to hang. What is the “2\>&1” supposed to do? Does that pipe > stderr into stdout? Yes. Exactly that. ---
**Author:** ![snowbird122](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c68b51/32.png) [@snowbird122](https://www.ruby-forum.com/u/snowbird122)\ **Post date:** [March 13, 2008, 4:11am UTC](https://www.ruby-forum.com/t/trouble-capturing-output-of-spawned-process/131764/5 "2008-03-13T04:11:17Z")
Actually, it looks like the 2\>&1 syntax might be working. I think the last time I ran the script, it paused to ask me if I wanted to overwrite a file, since I didn’t see the prompt, I wasn’t able to repond. If the file doesn’t exist, it seems to complete just fine. A second test I just did confirmed this. ---
**Author:** ![snowbird122](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/c68b51/32.png) [@snowbird122](https://www.ruby-forum.com/u/snowbird122)\ **Post date:** [March 13, 2008, 11:17am UTC](https://www.ruby-forum.com/t/trouble-capturing-output-of-spawned-process/131764/6 "2008-03-13T11:17:04Z")
Eric M. wrote: > last time I ran the script, it paused to ask me if I wanted to overwrite > a file, since I didn’t see the prompt, I wasn’t able to repond. If the If that’s going to be an issue you can use IO#popen to control it more interactively.