@item psnr
Set error[?] variables during encoding.
@item truncated
+@item drop_changed
+Don't output frames whose parameters differ from first decoded frame in stream.
+Error AVERROR_INPUT_CHANGED is returned when a frame is dropped.
@item ildct
Use interlaced DCT.
@item nokey
Discard all frames excepts keyframes.
+@item nointra
+Discard all frames except I frames.
+
@item all
Discard all frames.
@end table