内容简介:This article is not meant to dive into a complete solution or tool. It's going to describe a concept and a simple script that I'm working on and I think will make my relationship with(Yes I know that theFFmpeg is a very useful tool. It comes with a variety
ffcms - FFmpeg's -filter_complex made simple
This article is not meant to dive into a complete solution or tool. It's going to describe a concept and a simple script that I'm working on and I think will make my relationship with FFmpeg easier. Maybe yours too? (:
(Yes I know that the FFmpeg
project provides more than only the ffmpeg
binary. But, in this art, when saying FFmpeg
I mean the ffmpeg
binary only.)
Table of Contents
FFmpeg
FFmpeg is a very useful tool. It comes with a variety of options, codecs and generally stuff that you may need while operating on media files.
For simple tasks, the tool is very straightforward. You want to convert a video? Beng: ffmpeg -i input.mov output.mp4
. You want to remove audio from a video? Beng beng: ffmpeg -i input.mov -an output.mov
.
Simplicity is very important but there are cases when you need to do more complex stuff. E.g. you want to put a video on top of another, bigger one, then you want to adjust colors a little and then...
Yee.. The wishlist can escalate quickly. But, fear no more! FFmpeg is right here for you. Well, you just need to know how to use it. So you google it. FFmpeg put video on another
. You quickly find out that it is called overlaying
and you must use a filter named, you guessed it, overlay
. Fortunately FFmpeg
's community is helpful and you find similar problem at stackoverflow
. The command is:
ffmpeg -i input.mov -i overlay.mov \ -filter_complex "[1:v]setpts=PTS-10/TB[a]; \ [0:v][a]overlay=enable=gte(t\,5):shortest=1[out]" \ -map [out] -map 0:a \ -c:v libx264 -crf 18 -pix_fmt yuv420p \ -c:a copy \ output.mov
Back in the days, when I found an answer like this I was like
At the end, it's not THAT bad. You can actually guess what some of these mean:
-
input.mov
andoverlay.mov
are probably videos that I want to use. -
-i
is used twice, which is strange, but it's always followed by a video that I have on disk, so it probably meansinput
. -
-filter_complex
it's followed by a string which.. ee.. has square brackets.. oh, there is a Python slicing! It's a Python script? It computes10 / terabyte
, substracts it fromPTS
and assigns it to a variable calledsetpts
. Hmm, why is there a semicolon? Python doesn't need them. I'll get back to it later.. -
-map
so we map[out]
whathever that is and then we-map
another Thing. Why not? I'll take that. -
-c:v
.. I refuse.
Of course, that's an exaggeration. But, there is a grain of truth in it, don't you think?
ffcms
The -filter_complex
argument is the one that the article is about. I want to describe an idea for a tool that simplifies constructing FFmpeg
command that is supposed to use -filter_complex
.
(Yep, I know that more arguments understand filtering graph syntax, but let's not bother about it here)
The idea
The concept is actually very simple. Instead of writing a FFmpeg
command at once in terminal, you write a JSON that describes what the command's supposed to do. Then you pass the JSON to ffcms
tool and it prints a complete ffmpeg
command that just can't wait to be run. If you're a visual person:
Examples
Original 2x2 grid
FFmpeg
provides an example of -filter_complex
usage to create a grid out of one video. It can be found here: https://trac.ffmpeg.org/wiki/FilteringGuide#Multipleinputoverlayin2x2grid
.
The command there is:
ffmpeg -f lavfi -i testsrc -f lavfi -i testsrc -f lavfi -i testsrc -f lavfi -i testsrc -filter_complex \ "[1:v]negate[a]; \ [2:v]hflip[b]; \ [3:v]edgedetect[c]; \ [0:v][a]hstack=inputs=2[top]; \ [b][c]hstack=inputs=2[bottom]; \ [top][bottom]vstack=inputs=2[out]" -map "[out]" -c:v ffv1 -t 5 multiple_input_grid.avi
Let's break it down:
-
ffmpeg
- TheFFmpeg
binary you want to run. -
-f lavfi -i testsrc
- declaration of an input. The input format islavfi
, the input file istestsrc
. This is duplicated four times to imitate four different inputs. -
-filter_complex
- that's the place where magic takes place.-
[1:v]negate[a]
- Take the video from input at index1
, usenegate
filter on it and 'save' output of the filter to a link nameda
. -
[2:v]hflip[b]
- Take the video from input at index2
, usehflip
filter on it and 'save' output of the filter to a link namedb
. -
[3:v]edgedetect[c]
- Take the video from input at index3
, useedgedetect
filter on it and 'save' output of the filter to a link namedc
. -
[0:v][a]hstack=inputs=2[top]
- Take two inputs: the video from input at index0
and something that is in the linka
(which is output of[1:v]negate
filtering). Then, on these two inputs, perform filter namedhstack
with one parameterinputs
that is set to2
. Save the result in link namedtop
-
[b][c]hstack=inputs=2[bottom]
- Similar to above. Take two inputs from linksb
andc
perform filterhstack
with parameterinputs
set to2
. Save the result in link namedbottom
. -
[top][bottom]vstack=inputs=2[out]
- take two inputs from linkstop
andbottom
, performvstack
filter with paraminputs
set to2
and save the result in link namedout
.
-
-
-map
- map stuff from link namedout
as input to next arguments. -
-c:v ffv1
- use FFV1 codec for video. -
-t 5
- result should be a 5 second video -
multiple_input_grid.avi
- the name of the output video.
Whoa, that's a lot. The result is something like this (source: https://trac.ffmpeg.org/attachment/wiki/FilteringGuide/multiple input overlay.jpg ):
ffcms style
I don't have the original testsrc
file, so I'll use part of the timelapse video that I made for my fiancée. Here's a gif made out of the original video:
(BTW, she paints the best mugs in the world, check it out: ig/fingers.in.paint )
To be 99% accurate, let's change the above ffmpeg
command to use my timelapse.mov
(the 1% is the removed -f lavfi
arguments):
ffmpeg -i timelapse.mov -i timelapse.mov -i timelapse.mov -i timelapse.mov -filter_complex \ "[1:v]negate[a]; \ [2:v]hflip[b]; \ [3:v]edgedetect[c]; \ [0:v][a]hstack=inputs=2[top]; \ [b][c]hstack=inputs=2[bottom]; \ [top][bottom]vstack=inputs=2[out]" -map "[out]" -c:v ffv1 -t 5 timelapse_grid.avi
Now let's write a JSON file that ffcms
would convert to a command like the above one. Here's the whole JSON:
{
"in": [
{
"id": "first_input",
"file": "timelapse.mov"
},
{
"id": "second_input",
"file": "timelapse.mov"
},
{
"id": "third_input",
"file": "timelapse.mov"
},
{
"id": "fourth_input",
"file": "timelapse.mov"
}
],
"out": "timelapse_grid.avi",
"filters": [
{
"in": "second_input",
"filter": "negate",
"out": "a"
},
{
"in": "third_input",
"filter": "hflip",
"out": "b"
},
{
"in": "fourth_input",
"filter": "edgedetect",
"out": "c"
},
{
"in": [
"first_input",
"a"
],
"filter": "hstack",
"out": "top"
},
{
"in": [
"b",
"c"
],
"filter": "hstack",
"out": "bottom"
},
{
"in": [
"top",
"bottom"
],
"filter": "vstack",
"out": "out"
}
]
}
Breaking down.
"in"
The top-level "in"
is an array of inputs that you'd pass after -i
argument to ffmpeg
binary. They are in the same order as you'd write them in the command line. It's used to let ffcms
know what the input media files are and to assign a meaningful "id"
s to the files. Thanks to that, in "filters"
you can refer to them using e.g. first_input
, not 0:v
.
"out"
The top-level "out"
is just the name of the output video.
"filters"
The top-level "filters"
are the filters that you'd write in the string provided to -filter_complex
argument.
E.g. the first filter:
{
"in": "second_input",
"filter": "negate",
"out": "a"
}
is equivalent of the [1:v]negate[a]
filter in -filter_complex
's string.
Mind the hstack
and vstack
filters. In -filter_complex
string you need to pass number of inputs like: [b][c]hstack=inputs=2[bottom]
. In ffcms
JSON you write:
{
"in": [
"b",
"c"
],
"filter": "hstack",
"out": "bottom"
}
The number of inputs is well-known. It's the number of elements in the "in"
array, so ffcms
adds inputs=2
to the result command on its own.
Renaming ids
Actually, I don't like the names of the ids. a
, b
and c
? Let's make them more meaningful:
"filters": [
{
"in": "second_input",
"filter": "negate",
"out": "negated"
},
{
"in": "third_input",
"filter": "hflip",
"out": "flipped"
},
{
"in": "fourth_input",
"filter": "edgedetect",
"out": "edged"
},
{
"in": [
"first_input",
"negated"
],
"filter": "hstack",
"out": "top"
},
{
"in": [
"flipped",
"edged"
],
"filter": "hstack",
"out": "bottom"
},
{
"in": [
"top",
"bottom"
],
"filter": "vstack",
"out": "out"
}
]
FFmpeg command
After creating the JSON, you can pass it to ffcms
. With the JSON above it prints such FFmpeg
command:
ffmpeg -y -i timelapse.mov -i timelapse.mov -i timelapse.mov -i timelapse.mov -filter_complex \ "[1:v]negate[negated]; \ [2:v]hflip[flipped]; \ [3:v]edgedetect[edged]; \ [0:v][negated]hstack=inputs=2[top]; \ [flipped][edged]hstack=inputs=2[bottom]; \ [top][bottom]vstack=inputs=2[out]" \ -map "[out]" -c:v ffv1 timelapse_grid.avi
Now you can just grab it and run in terminal.
Here you can see a gif created out of the result video:
Cameraman
Now let's go further and make our wishlist a little more complex. Let's create a grid, like in the previous example. Additionally, let's overlay an image on top of edged
video part. We want to overlay it at given x
and y
. Plus, we want to make it visible for the first three seconds only.
First of, the most important. The Cameraman:
Now let's adjust JSON to handle additional requirements.
Adding input media
We need to let ffcms
know that there is another input media file. Let's add it to the top-level "in"
array:
"in": [
{
"id": "cameraman",
"file": "cameraman.png"
}
]
We need to add one more filter to the top-level filters list - overlay
. There we use edged
and cameraman
as its inputs:
"filters": [
{
"in": [
"edged",
"cameraman"
]
}
]
Next we define the filter:
"filters": [
{
"in": [
"edged",
"cameraman"
],
"filter": {
"name": "overlay",
"params": {
"x": 200,
"y": 100,
"enable": "'between(t,0,3)'"
}
}
}
]
x
and y
are obvious but enable
not so much. The enable
parameter tells when the cameraman
input should be visible on top of the edged
one. We specify here, that it should be visible when time ( t
) is between
0
and 3
second.
Now, the last thing is to specify the output link id:
"filters": [
{
"in": [
"edged",
"cameraman"
],
"filter": {
"name": "overlay",
"params": {
"x": 200,
"y": 100,
"enable": "'between(t,0,3)'"
}
},
"out": "cameraman_on_edges"
}
]
Cool. Now we just need to use cameraman_on_edges
in one of the hstack
filters:
"filters": [
{
"in": [
"flipped",
"cameraman_on_edges"
],
"filter": "hstack",
"out": "bottom"
}
]
And that's it. The full JSON looks like this:
{
"in": [
{
"id": "first_input",
"file": "timelapse.mov"
},
{
"id": "second_input",
"file": "timelapse.mov"
},
{
"id": "third_input",
"file": "timelapse.mov"
},
{
"id": "fourth_input",
"file": "timelapse.mov"
},
{
"id": "cameraman",
"file": "cameraman.png"
}
],
"out": "timelapse_grid.avi",
"filters": [
{
"in": [
"second_input"
],
"filter": "negate",
"out": "negated"
},
{
"in": [
"third_input"
],
"filter": "hflip",
"out": "flipped"
},
{
"in": [
"fourth_input"
],
"filter": "edgedetect",
"out": "edged"
},
{
"in": [
"edged",
"cameraman"
],
"filter": {
"name": "overlay",
"params": {
"x": 200,
"y": 100,
"enable": "'between(t,0,3)'"
}
},
"out": "cameraman_on_edges"
},
{
"in": [
"first_input",
"negated"
],
"filter": "hstack",
"out": "top"
},
{
"in": [
"flipped",
"cameraman_on_edges"
],
"filter": "hstack",
"out": "bottom"
},
{
"in": [
"top",
"bottom"
],
"filter": "vstack",
"out": "out"
}
]
}
ffcms
outputs such command:
ffmpeg -i timelapse.mov -i timelapse.mov -i timelapse.mov -i timelapse.mov -i cameraman.png -filter_complex \ "[1:v]negate[negated]; \ [2:v]hflip[flipped]; \ [3:v]edgedetect[edged]; \ [edged][4:v]overlay=enable='between(t,0,3)':x=200:y=100[cameraman_on_edges]; \ [0:v][negated]hstack=inputs=2[top]; \ [flipped][cameraman_on_edges]hstack=inputs=2[bottom]; \ [top][bottom]vstack=inputs=2[out]" \ -map "[out]" -c:v ffv1 timelapse_grid.avi
and the result video looks like this:
Conclusion
Please note that ffcms
is not a finished tool. There is still much work to do. Contributions are welcome (:
Nevertheless, it's usable enough for me to use it with helping my fiancée with her stuff, so that's for sure a good start.
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