Loading external files/lavfi-complex playback

[willwrong]

Hi all,

I'm attempting to load a video with an alpha'd overlay using --external-files and then --lavfi-complex, like the following MPV command:

mpv --fs --external-file="overlay.mov" "video.mov" --lavfi-complex="[vid1][vid2]overlay[vo]"

I found an earlier Issue (https://github.com/jaseg/python-mpv/issues/34) that somewhat addresses this but I can't seem to find any more information on the exact syntax to implement this with the API. Any help is most appreciated!

[neinseg]

Hi there,

you're right, this is currently a bit complicated. Here's how you do it:

import mpv

player= mpv.MPV()
player.loadfile('tests/test.webm', external_files='big-buck-bunny_trailer.webm',
    lavfi_complex='"[vid2]scale=1280:720[scaled];[vid1][scaled]blend=shortest=1:all_mode=overlay:all_opacity=0.7[vo]"')
player.wait_for_playback()

Things to note:

• Since these options are specific to the playing file, I think you should pass them in through the loadfile command.
• Due to some limitations around libmpv and python-mpv, you have to pass in a pair of double quotes around the lavfi-complex. I'm working on a better solution, but if you do it like this, it will likely continue to work in the future.
• You don't have to pass in the "main" vid=1 video file with external-files, you pass it in as the URL argument to loadfile.

[willwrong]

Thanks for the advice! Will test and implement.

[willwrong]

That's working well! Thank you. Another quick one: is there any way you know of to control the [vid1] stream independently of the overlay? I'm searching for a way to have an overlaid video play uninterrupted while the video underneath changes, or even vice-versa. I'm currently using the loadfile command to cue the video switch, but obviously that causes a hard cut in the overlay. Any ideas are welcome, and thanks again.

[neinseg]

I have had a look around and it seems that mpv is re-loading all external_files every time it loads a new file through either loadfile or from a playlist. The only idea I have on how you could get this working with lavfi-complex would be to use https://mpv.io/manual/master/#options-track-auto-selection and try to just never actually quit playing, and just switch out the inputs to the lavfi-complex.

Depending on what you want to achieve there may be several simpler options though: First, you can directly feed mpv image overlays from python, see here. Second, python-mpv has OpenGL support, see here. Using that you could just have two separate mpv.MPV() objects play the two videos into OpenGL buffers that you can then overlay using OpenGL. You can also sync up these two separate instances from python by seeking.

[willwrong]

Thanks again for the advice -- I'll experiment with these!