Building Frames
Building Frames
FFmpeg is good not only for converting and fusing videos together, it can also generate streams on the fly, which you can then use for compositing and effects.
The casual user might only use the FFmpeg multimedia framework for converting from one audio or video format to another, but FFmpeg can do much more than that. I'll take a look at one of FFmpeg's most powerful secret weapons: the lavfi virtual device.
Using lavfi
FFmpeg's lavfi (short for libavfilter) virtual device sounds more complicated than it really is. Instead of using prerecorded video or audio files as streams, lavfi lets you create streams out of thin air. You can use these streams on the fly and combine them with clips and other dynamically generated streams (e.g., from a webcam or microphone) to create your output file.
Maybe it is better explained with an example:
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