[Bug 796519] Add AV1 codec parser

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=796519

--- Comment #7 from Georg Ottinger <g.ottinger at gmx.at> ---

many thanks for your feedback. For most of them I can just go ahead and
implement the changes.

I do want to note two things:

1.) About CamelCase - I tried to stick two the AV1 Bitstream Spec - and in my 
understanding its using underscore notation for "direct" read bits from the
stream and CamelCase if there is some calculation involved.

-> here the question is what is better: Sticking to the original notation from
the Spec? Or following the gstreamer standard layout?

2.) About reserving space in the structs. 
itu_t_t35_payload_bytes[] is not defined in the Spec - thus it is unclear to me
how many bytes to reserve.

Quote from the Spec: "Note: The exact syntax of itu_t_t35_payload_bytes is not
defined in this specification. External specifications can
define the syntax. From a decoder perspective, it suffices to say that decoders
should ignore the entire OBU if they don’t understand it. The last byte of the
valid content of the data is considered to be the last byte that is not equal
to zero. This rule is to prevent the dropping of valid bytes by systems that
interpret trailing zero bytes as a padding continuation of the trailing bits in
an OBU. This implies that when any payload data is present for this OBU type,
at
least one byte of the payload data (including the trailing bit) shall not be
equal to 0."

-> Should I follow the advise and ignore the entire OBU?

coded_tile_data[] - its size is variable with a maximum of 64KB per tile list
entry. (and there are max. 512 of tile_list_entries) ... I can't allocate this
statically.

-> Maybe I should reserve a pointer for this? (this would also need a API
function for freeing the space after use)

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