<p><code>[0:v][v0]</code> and <code>[2:v][v2]</code> don't contain any filter declaration, and thus ffmpeg complains. Insert whichever filter is desired in between the input and output pads.</p>
<p>I suppose you meant to scale the heights of the 3 inputs to match. In which case,</p>
<p><code>ffmpeg -i in.mp4 -i in2.mkv -i in3.mkv \ -filter_complex &quot;[0:v]scale=-1:1440[v0];[1:v]scale=-1:1440[v1];[2:v]scale=-1:1440[v2];[v0][v1][v2]hstack=inputs=3&quot; -map &quot;[v]&quot; -map 1:a output.mp4</code></p>
<p>on input processing with -filter_complex, you use this pattern:</p>
<p><code>[input_number:v]operation[tmp_output_name]</code></p>

CC BY-SA 4.0
2020-12-04T07:46:26.510Z
I suggest an edit, please take a look.
Adi Prasetyo
CC BY-SA 4.0
2020-12-02T05:11:49.197Z
2020-12-04T08:04:32.437Z
2020-12-04T08:04:32.437Z
Gyan
<p>the desired output is combining 3 vids, and using scale or pad (do some processing on the input).</p>
<pre><code>ffmpeg -i in.mp4 -i in2.mkv -i in3.mkv \
-filter_complex &quot;[0:v][v0];[1:v]scale=-1:1440[v1];[2:v][v2],[v0][v1][v2]hstack=inputs=3&quot;
 -map &quot;[v]&quot; -map 1:a output.mp4
</code></pre>
<p>give:</p>
<blockquote>
<p>[AVFilterGraph @ 0xec0a80] No such filter: ''
Error initializing complex filters.
Invalid argument</p>
</blockquote>

CC BY-SA 4.0
2020-11-29T05:28:31.903Z
What are `[0:v][v0];` and `[2:v][v2],` meant to do?
Gyan
CC BY-SA 4.0
2020-12-01T20:37:00.653Z
there is the confusing part, the pattern on filtergraph, [in]opt_preprocess[out]?
Adi Prasetyo
<ffmpeg>
no such filter, when using filter complex with pre-scale
Adi Prasetyo
# no such filter, when using filter complex with pre-scale

(Asked by: username_0 on 2020-11-28)

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

give:

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

**Tags:** ffmpeg

> **Comments:**
> **username_1**: What are `[0:v][v0];` and `[2:v][v2],` meant to do?  
> **username_0**: there is the confusing part, the pattern on filtergraph, [in]opt_preprocess[out]?  

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## 1 answers

### Answer by username_1 on 2020-12-02. Score: 2 | Accepted answer

`[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:

`[input_number:v]operation[tmp_output_name]`

> **Comments:**
> **username_0**: I suggest an edit, please take a look.  

---

