How to combine multiple FFmpeg filters into single command?

Tech QnA
1

I have a video file and I want to crop some portion of the video, apply to a pad, and scale it to a particular dimension. I can do this using three FFmpeg commands each time using a specific filter but I want to do it in a single FFmpeg command, is there any way?

2

John,

Combining multiple filters into a single FFmpeg command is very simple, you must be using the -vf option provided by FFmpeg for your individual filters, but to combine them into a single command you have to create a filter chain and use it with the -filter_complex option provided by FFmpeg.

For example,
ffmpeg -i input.mp4 -filter_complex "[0:v]filter1=option1:option2[outv];[0:a]filter2=option3:option4[outa]" -map "[outv]" -map "[outa]" output.mp4

  • -i input.mp4 indicates the input file, in this case, input.mp4.

  • -filter_complex is used to target the complex filter graph.

  • [0:v] refers to the video stream from the first input (index 0).

  • filter1=option1:option2 shows the first filter you wish to apply to the video stream.

  • [outv] is the name given to the output video stream from the filter.

  • [0:a] refers to the audio stream from the first input (index 0).

  • filter2=option3:option4 shows the second filter you want to apply to the audio stream.

  • [outa] is the name given to the output audio stream from the filter.

  • -map "[outv]" and -map "[outa]" specify which output streams to include in the final output file.

  • output.mp4 is the name of the output file.

And you can also use the filters twice in different commands and complex filters in ffmpeg.
I hope this may help you! Ask if you need further guidance.

Thanks

3

Can you tell me how can I use this option mentioned above? I tried this on my system but it did not work properly maybe I am missing something!

4

Sure!
FFmpeg filter chain works in a very simple way just like a normal programming language, you get a hold of a particular stream (video/audio/subtitle), apply some operation (filter) on it, and store the output stream in a variable that can be referenced later in filter chain anywhere or can be passed to video codec for transcoding purpose.

Usually, these filter chains follow syntax like the one given below.

[index_of_stream:type_of_stream]filter_1_name=param1=value1:param2=value2[output_of_filter_1];[output_of_filter_1]filter_2_name[final_output]

For your use case, the filter chain would look like the following.

[0:v]crop=x=0:y=0:w=500:h=500[cropped_stream];[cropped_stream]pad=width=500:height=500:x=0:y=40:color=black[padded_stream];[padded_stream]scale=w=300:h=300[scaled_stream]

5

You can just put the filter chain constructed in the above example into the FFmpeg command like the following.

ffmpeg -i input.mp4 -filter_complex "[0:v]crop=x=0:y=0:w=500:h=500[cropped_stream];[cropped_stream]pad=width=500:height=500:x=0:y=40:color=black[padded_stream];[padded_stream]scale=w=300:h=300[scaled_stream]" -map "[scaled_stream]" -c:v libx264 -f mp4 output.mp4

6

Although it can be effective to combine several FFmpeg filters into a single command, what should you take into account if the filters are incompatible or dependent on one another? What would happen, for example, if the watermark in your first example needed to be repositioned because of the size change of the video?

7

The order in which the filters are applied is crucial to take into account when merging several FFmpeg filters into a single command. The sequence in which filters are processed from left to right can affect the result. In the first example, where we resize the video and add a watermark, you should place the watermark filter after the scale filter if the watermark’s position relies on the size of the video after resizing:

ffmpeg -i input.mp4 -vf "scale=1280:720,eq=brightness=1.2,drawtext=text='Watermark Text':x=10:y=10:fontsize=24:fontcolor=white" output.mp4

This makes sure that the watermark is added after scaling and that its location is in relation to the size of the scaled video. For the intended outcomes, take into account the order in which the filters are applied.