While it is a per-frame variable, it is only really used in the
low-level decoding code, so it is more efficient to store it in the
slice context.

There is no need to store a whole H264Picture, with a full AVFrame
embedded in it. This should allow getting rid of the embedded AVFrame
later.

This code makes no sense for h.264.

There is now no need to have per-slice copies of the H264Context.

All the variables modified by this code are either per-MB arrays or have
been moved to the per-slice context

h264dec does not use them at all and only allocates them for ER.

Also change the method for allocating to the same one as used by
edge_emu_buffer.

Also change the method for allocating them. Instead of two possible
alloc calls from different places, just ensure they are allocated at the
start of each slice. This should be simpler and less bug-prone than the
previous method.

All the variables modified by this code are either per-MB arrays or have
been moved to the per-slice context

All the variables modified by this code are either per-MB arrays or have
been moved to the per-slice context

All the variables modified by this code are either per-MB arrays or have
been moved to the per-slice context

All the variables modified by this code are either per-MB arrays or have
been moved to the per-slice context

All the variables modified by this code are either per-MB arrays or have
been moved to the per-slice context

It is read-only in this code.

All the variables modified by this code are either per-MB arrays or have
been moved to the per-slice context

All the variables modified by this code are either per-MB arrays or have
been moved to the per-slice context

All the variables modified by this code are either per-MB arrays or have
been moved to the per-slice context

Use a local variable instead.