lavd/v4l2: extend error/debug feedback in case of invalid codec/pix_fmt
lavd/v4l2: fix misc messages
lavd/v4l2: return meaningful error code from device_init()

In particular, propagate errno value in case of device init failure.
lavd/v4l2: apply grammar/consistency fixes to options help fields
lavf/http: add HTTP protocol cookie support

Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
doc/protocols: document HTTP protocol cookie support

Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
tools: add plotframes script

The script is ported from ffprobe/SourceForge and updated to the current
ffprobe version.
examples/demuxing: free AVPacket after usage

Fix leak.
h264: add 3 pixels below for subpixel filter wait position.

If the motion vector is at a subpixel position, we need 3 pixels below
the motion vector's wholepel position available, not 2, since the MC
filter is a sixtap filter for the hpel position, and then a bilin filter
for the qpel position.

This patch fixes highly irreproducible (0.1%) fate failures in frame 2
and 4 of h264-conformance-cama2_vtc_b (e.g. first P-frame, first field,
last line of MB x=40,y=2 and second field and last lines of MBs x=39-40,
y=3). These used pre-loopfilter instead of post-loopfilter data because
the await_progress() waited for one line too little in that field, and
the motion vector of these particular MBs happened to align exactly to a
position where that demonstrates the bug.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>