Since 1d9c5e3b performRender feeds swap timing to mpv via
mpv_render_context_report_swap, but only after presentRenderbuffer -
which is skipped while PiP is active. Once swap reports stop mid-stream,
display-vdrop's vsync estimation goes stale and mpv drops nearly every
frame (vo drop counter climbing ~19/s on a 24fps stream), turning PiP
into a slideshow.
The frame is genuinely displayed during PiP via the
AVSampleBufferDisplayLayer, so report the swap on that path too.
4effe5d7a5