[Libav-user] Programmatically blend two frames using libavfilter

[alexander_eroma at htc.com]

Hello
I need to programmatically draw an image over the video frame when encoding video via libavcodec. (which is part of ffmpeg). As I understand I need to use libavfilter tools to do this.
I can access AVFilter via avfilter_get_by_name("blend"). Also I can access filter graph viaavfilter_graph_create_filter(&filterCtx, filter, "blender", NULL, NULL, fgr). But I can not understand what should I do next.
I have two AV frames, for example:
AVFrame* bottomFrame;
AVFrame* topFrame;
How can I put topFrame over the bottomFrame using libav API?
Thank you

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