Golang command working in terminal but not with exec package

Question

I am converting a video generation library from NodeJS to GO that primarily uses FFMPEG for all the video processing. I already have all the FFMPEG commands written out to do the generation I want. The issue is that when I try to run the command through the os/exec package, it fails. However, if I copy the exact command and run it directly in the terminal it works and I cannot figure out why that is. My code that runs the command is below:

command := "ffmpeg -y -loop 1 -i image.png -vf 'fade=in:0:15,fade=out:105:15' -c:v mpeg2video -t 5 -s 1280x720 -r 30 -q:v 1 -preset ultrafast image.mpg"

parts := strings.Fields(command)
cmd := exec.Command(parts[0], parts[1:]...)
cmd.Stderr = os.Stderr
cmd.Stdout = os.Stdout
err := cmd.Run()
if err != nil {
    panic(err)
}

The ffmpeg error I get when I try to run this code is:

[AVFilterGraph @ 0x22a9bc0] No such filter: 'fade=in:0:15,fade=out:105:15'

Error opening filters!

2016/08/17 17:48:53 exit status 1

Like I previously stated, if I copy the EXACT command:

ffmpeg -y -loop 1 -i image.png -vf 'fade=in:0:15,fade=out:105:15' -c:v mpeg2video -t 5 -s 1280x720 -r 30 -q:v 1 -preset ultrafast image.mpg

and run it directly in the terminal, it works no problem.

PLEASE HELP.

abhink abhink · Accepted Answer · 2016-08-17T18:06:26

When you are using strings.Fields(command), the fields are being split on spaces. This results in the parts slice containing a value 'fade=in:0:15,fade=out:105:15', with quotes. This complete value (with quotes) is being passed to the ffmpeg command, which the command is unable to recognize.

A shell would strip off these quotes and pass the string fade=in:0:15,fade=out:105:15 only which Go isn't doing. To fix, try:

// remove the quotes around fade=in:0:15,fade=out:105:15
command := "ffmpeg -y -loop 1 -i image.png -vf fade=in:0:15,fade=out:105:15 -c:v mpeg2video -t 5 -s 1280x720 -r 30 -q:v 1 -preset ultrafast image.mpg"

parts := strings.Fields(command)

Golang command working in terminal but not with exec package

1 Answers