How do I resolve ffmpeg concat command error "unknown keyword..."?

I am trying to concatenate two video files using ffmpeg, and I am receiving an error.

To eliminate compatibility issues between the two videos, I have been concatenating the same video with itself, and the same error persists.

ffmpeg \
  -f concat \
  -safe 0 \
  -i intro_prepped.avi intro_prepped.avi \
  -c copy \
  concat.avi

And the error output I receive is....

[concat @ 0x220d420] Line 1: unknown keyword 'RIFFf�?' intro_prepped.avi: Invalid data found when processing input

I have tried various combinations of concat flags and have not been able to get it to work. Has anyone seen this error before?

Solution

Docs for several ways of concatenating files: https://trac.ffmpeg.org/wiki/Concatenate

Here's a command I use to concatenate videos:

ffmpeg \
  -i "concat:input1.avi|input2.avi|input3.avi" \
  -c:a copy \
  -c:v copy \
  output.avi