Procs
proc av_tx_init(ctx: ptr ptr AVTXContext; tx: ptr av_tx_fn; type: AVTXType; inv, len: cint; scale: pointer; flags: uint64): cint {.importc, cdecl, ...raises: [], tags: [], forbids: [].}
proc av_tx_uninit(ctx: ptr ptr AVTXContext) {.importc, cdecl, ...raises: [], tags: [], forbids: [].}