[Bug 755068] New: gstreamer: Revisit GstAllocationParam vs GstVideoAlignment

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=755068

            Bug ID: 755068
           Summary: gstreamer: Revisit GstAllocationParam vs
                    GstVideoAlignment
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gstreamer (core)
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: nicolas.dufresne at collabora.co.uk
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

In 1.5 development, we've hit this issue where the
VideoAlignment.stride_align[] would be greater then the allocation params. This
was an upstream pipeline bug, but we thought it is nicer to make downstream
(the pools) safe to that, specially that it can figure-out and that the strictp
values depends on the number of allocation.

In the quick solution to get the release out, we simply maxed out all the
alignment to the highest. This is "over" aligning the memory, and we could
clean this up to be more strict.

There is two main cases, the basically when there is multiple allocations (1
GstMemory per plane) and when there is a single allocation.

In the single allocation case, the adjustment shall be:

  mem_align = max(mem_align, stride_align[1], ..., stride_align[n] ...)
  stride_align[n] = max(stride_align[n], stride_align[n+1], ...)

The reason of this cascade, is that each alignment impact the initial alignment
of the following. Maximizing everything to the biggest is also correct, but
would not be strict enough for a verifying the minimum alignment requirement is
met.

In the multiple allocation case, it's simplier.

  mem_align = max(mem_align, stride_align[n])
  stride_align[n] = stride_align[n]

This is because with split allocation, a plane have no impact on the alignment
of the following plane.

This is a minor enhancement, reducing of only few bytes the allocation. Though,
the idea with this enhancement bug is to create a new utility method, similar
to gst_video_info_align() that would at once align the GstVideoInfo and the
GstAllocationParam, to which the type of allocation is passed (single or
multiple). This way we can remove custom code that has been added everywhere,
and then have this implemented in a single location.

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