Use the unit type table to determine what we need to do to clone the
internals of the unit content when making copies for refcounting or
writeability. (This will still fail for units with complex content
if they do not have a defined clone function.)
Setup and naming from a patch by Andreas Rheinhardt
<andreas.rheinhardt@gmail.com>, but with the implementation changed
to use the unit type information if possible rather than requiring a
codec-specific function.
Unit types are split into three categories, depending on how their
content is managed:
* POD structure - these require no special treatment.
* Structure containing references to refcounted buffers - these can use
a common free function when the offsets of all the internal references
are known.
* More complex structures - these still require ad-hoc treatment.
For each codec we can then maintain a table of descriptors for each set of
equivalent unit types, defining the mechanism needed to allocate/free that
unit content. This is not required to be used immediately - a new alloc
function supports this, but does not replace the old one which works without
referring to these tables.
All cbs-functions to write units share a common pattern:
1. They check whether they have a write buffer (that is used to store
the unit's data until the needed size becomes known after writing the
unit when a dedicated buffer will be allocated).
2. They use this buffer for a PutBitContext.
3. The (codec-specific) writing takes place through the PutBitContext.
4. The return value is checked. AVERROR(ENOSPC) here always indicates
that the buffer was too small and leads to a reallocation of said
buffer.
5. The final buffer will be allocated and the data copied.
This commit factors this common code out in a single function in cbs.c.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
The type of the result of a shift operation is unaffected by the type of
the right operand, so some existing code overflows with undefined behaviour
when the element length is 32. Add a helper macro to calculate the maximum
value correctly and then use it everywhere this pattern appears.
Found-by: Andreas Rheinhardt <andreas.rheinhardt@googlemail.com>
This makes it easier for users of the CBS API to get alloc/free right -
all subelements use the buffer API so that it's clear how to free them.
It also allows eliding some redundant copies: the packet -> fragment copy
disappears after this change if the input packet is refcounted, and more
codec-specific cases are now possible (but not included in this patch).
Anton Khirnov
James Almer
Mark Thompson
Andreas Rheinhardt