yamitranscode will copy input to output if it can can't decide output format.

[xuguangxin]

when yamitranscode cannot determine the output codec and the input is a yuv (I420 or NV12) it will apparently hang when in reality is just copying the input YUV to the output without processing

[wudping]

hi @xuguangxin , how about just print a error log of "can't guess the output codec format", instead of copying? I think, user can use command "cp" to do it; and as I know, transforming NV12 to I420 is enabled by yamivpp.