On Tue, 14 Dec 2021, James Almer wrote:
On 12/14/2021 3:54 PM, Nicolas George wrote:
James Almer (12021-12-14):
We add a const uint8_t* field to AVChannelCustom. If the user wants to
allocate the strings instead, and not worry about their lifetime, they
can
provide the layout with a custom free() function that will take care of
cleaning anything they came up with on uninit().
I understood what you suggested, and it amounts to letting API users
fend for themselves. We can do that, but I would prefer if we only did
on last resort, if we do not find a more convenient solution.
There's "char name[16]". Bigger than a pointer (Could be 8 bytes instead, but
then it's kinda small). The user will not have to worry about the lifetime of
anything then.
I'm attaching a diff that goes on top of the last patch of this set
implementing this. It also adds support for these custom names to
av_channel_layout_describe(), av_channel_layout_index_from_string() and
av_channel_layout_channel_from_string(), including tests.
I'd rather not mix custom labels with our fixed names for channels. E.g.
what if a label conflicts with our existing channel names? If the user
wants to specify a channel based on its label, that should be a separate
syntax IMHO.
Overall, having a char name[16] is still kind of limiting, e.g. a label
read from a muxed file will be truncated, I'd rather not have anything.
Here is one more idea, kind of a mix of what I read so far: Let's refcount
only the dynamically allocated part of AVChannelLayout. Something like:
typedef struct AVChannelLayout {
enum AVChannelOrder order;
int nb_channels;
uint64_t mask;
AVBufferRef *custom;
} AVChannelLayout;
And the reference counted data could point to an array of AVChannelCustom
entries. And AVChannelCustom can have AVDictionary *metadata, because it
is refcounted.
Regards,
Marton
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