ffplay multiple input files

For synthesized streams like sine we can do it e.g.

ffplay -autoexit -nodisp -f lavfi -i '
sine=frequency=500[a];
sine=frequency=1000[b];
[a][b]amerge, atrim=end=2
'

but it does not seem to accept multiple -i for some reason. So is there a way to open a file from some filter? E.g.:

ffplay -i tmp.wav -i tmp.mkv -filter_complex "[0:a]atrim=end=2[a];[1:v]trim=end=2[v]" -map '[a]' -map '[v]'

fails with:

Argument 'tmp.mkv' provided as input filename, but 'tmp.wav' was already specified.

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