add custom ffmpeg avfilter in mlt

Question

I created one custom filter under av filter and added it into ffmpeg. I build the ffmpeg and in ffmpeg its working fine and visible in ffmpeg filter list.

Now I tried to build mlt with this custom ffmpeg. mlt build successfully. I checked in mlt filters but it is not available.

On investigating I found in mlt there is no avfilter available which can take 2 videos as input. As my filter also takes 2 videos as input and apply some filter and output one video that's why it's not available.

Now I want to know

1. Why mlt is not supporting multiple input av filters ?
2. Where in code mlt restricted it.
3. What is the best way to add this filter ?

Answer 1

Why mlt is not supporting multiple input av filters ?

MLT Filter objects only support input from one source. So using an AV filter with multiple inputs can not work. This is fundamental to the design of MLT.

Where in code mlt restricted it.

https://github.com/mltframework/mlt/blob/master/src/modules/avformat/factory.c#L448

What is the best way to add this filter ?

MLT transitions can mix two frames from two different producers. It would be possible to design a new MLT transition similar to MLT filter that provides access to AV filters with two inputs.