playsink: Use signal handler IDs instead of disconnecting/blocking by function

This is cleaner and faster.
typefind: Add variant=itu to the h263 typefinder caps

https://bugzilla.gnome.org/show_bug.cgi?id=700770
decodebin: Connect and disconnect the have-type signal of typefind before starting/shutting down
decodebin: Use signal handler IDs instead of disconnecting by function

This is cleaner and faster.
Revert "decodebin2: use NO_RESYNC flag"

This reverts commit 0feecef2754ef208372eb39332b4f6fa2067d3d5.
decodebin: Lock the state of child elements as long as we manage their states

https://bugzilla.gnome.org/show_bug.cgi?id=690420
video: Always provide a buffer in gst_video_(enc|dec)oder_allocate_output_buffer()

We have no way of tell the caller of the exact error (e.g. if we're flushing),
so will have to wait until the caller uses API that returns a GstFlowReturn,
for example when pushing this buffer.

https://bugzilla.gnome.org/show_bug.cgi?id=700006
audio: Always provide a buffer in gst_audio_(enc|dec)oder_allocate_output_buffer()

We have no way of tell the caller of the exact error (e.g. if we're flushing),
so will have to wait until the caller uses API that returns a GstFlowReturn,
for example when pushing this buffer.

https://bugzilla.gnome.org/show_bug.cgi?id=700006
typefind: Ensure we have enough data when reading the sync marker in the AAC/LOAS typefinder
videoencoder: Don't require an output state to be set before allocating output buffers
videometa: fix docs
videoconvert: actually use the input pixels

Operate on the provided pixels array instead of the temp array.
video: move chroma functions to separate file
videoconvert: reformat
video: don't perform subsampling while packing

Don't perform subsampling when packing but let this be done by a
separate subsampling step.
video-chroma: add chroma resampler

Add functions to up/downsample chroma in horizontal and vertical
directions. These functions work in-placeand are meant to be used on the
input/output of the pack/unpack functions.
videotestsrc: subsample chroma before packing

Run the chroma subsampler before packing.
videoconvert: run chroma resamplers

Run the chroma upsampler after unpack and the chroma subsampler
before pack for higher quality conversions and correct chroma siting.
video-chroma: add interlaced flag
video-format: fix NV16 unpack

We can just use the NV12 functions, the only difference is the
vertical subsampling.