[FFmpeg-devel] Support for metadata in libavutil/eval.c

Stepan Bujnak stepanbujnak at fastmail.fm
Sun Jul 13 16:45:02 CEST 2014


I was thinking about introducing support for meta() function in the
expression evaluation language. As the ffmpeg filters gradually add
support for metadata, it would be convenient to do something like this:

> ffmpeg -i input.webm -vf cropdetect,crop=x=meta('lavfi.cropdetect.x'):y=meta('lavfi.cropdetect.y'):w=meta('lavfi.cropdetect.w'):h=meta('lavfi.cropdetect.x') output.webm

This fully automated crop is possible mainly thanks to cropdetect filter
that sets lavfi.cropdetect.* metadata. Now, as far as I know the
expression evaluation is now optimized to only work with double values,
therefore the re-implementation of the expression evaluation to accept
string arguments would not be trivial and so I ask you, would such
functionality be helpful and welcome?

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