Upipe
upipe-modules: add upipe_pad
Oh. Looks like I copy-pasted too much. Sorry and thank you for catching all that.
I need to copy because there seems to be no opportunity to modify the ubuf_mgr request that comes out of upipe_avcodec_decode (avcdec) when it is deported to a worker thread. avcdec calls its demand_ubuf_mgr function from UPIPE_HELPER_UBUF_MGR so it falls back to getting one from the probe when the request isn't answered in the normal manner. I assume it doesn't pass the thread boundary so it can't pass to the usual pipe we use, upipe_ntsc_prepend.
This is only something we recently discovered. Usually we have upipe_ffmt and upipe_sws between the two to convert to 4:2:2 but with that as input they don't need to do anything so they don't send their own asynchronous request for a ubuf_mgr which upipe_ntsc_prepend normally modifies.