the desired output is combining 3 vids, and using scale or pad (do some processing on the input).

ffmpeg -i in.mp4 -i in2.mkv -i in3.mkv \
-filter_complex "[0:v][v0];[1:v]scale=-1:1440[v1];[2:v][v2],[v0][v1][v2]hstack=inputs=3"
 -map "[v]" -map 1:a output.mp4


[AVFilterGraph @ 0xec0a80] No such filter: '' Error initializing complex filters. Invalid argument

  • What are [0:v][v0]; and [2:v][v2], meant to do?
    – Gyan
    Nov 29, 2020 at 5:28
  • there is the confusing part, the pattern on filtergraph, [in]opt_preprocess[out]? Dec 1, 2020 at 20:37

1 Answer 1


[0:v][v0] and [2:v][v2] don't contain any filter declaration, and thus ffmpeg complains. Insert whichever filter is desired in between the input and output pads.

I suppose you meant to scale the heights of the 3 inputs to match. In which case,

ffmpeg -i in.mp4 -i in2.mkv -i in3.mkv \ -filter_complex "[0:v]scale=-1:1440[v0];[1:v]scale=-1:1440[v1];[2:v]scale=-1:1440[v2];[v0][v1][v2]hstack=inputs=3" -map "[v]" -map 1:a output.mp4

on input processing with -filter_complex, you use this pattern:


  • I suggest an edit, please take a look. Dec 4, 2020 at 7:46

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