[FFmpeg-user] Selecting/dropping frames without re-encoding

[Marcelo Boufleur]

I'm not sure that what Mikhail wants really exists. If I understand
correctly, you want to retain original encoding and drop one frame every
two frames.

If this would be possible, you would have to work at the DNxHD inner level,
identify each frame start/end (by headers), bit-stream copy whichever
frames you would need, and then re-generate the DNxHD layer and headers to
reflect all the changes you have made.

I may be wrong, but I believe with current FFmpeg implementation you can
only work either with stream copy (if you don't want to change encoding,
nor frame rate, which defies his purpose), or use the previous suggestions
to cut framerate by half, which implies on re-encoding (which again, defies
his purpose).