Re: [FFmpeg-devel] [PATCH 001/289 v6] Add a new channel layout API

[James Almer <jamrial@gmail.com>]

On 1/19/2022 5:51 PM, Marton Balint wrote:
> 
> 
> On Tue, 18 Jan 2022, James Almer wrote:
> 
>> From: Anton Khirnov <anton@khirnov.net>
>>
>> The new API is more extensible and allows for custom layouts.
>> More accurate information is exported, eg for decoders that do not
>> set a channel layout, lavc will not make one up for them.
>>
>> Deprecate the old API working with just uint64_t bitmasks.
>>
>> Expanded and completed by Vittorio Giovara <vittorio.giovara@gmail.com>
>> and James Almer <jamrial@gmail.com>.
>> Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
>> Signed-off-by: James Almer <jamrial@gmail.com>
>> ---
>> Changes since last version:
>>
>> *av_channel_layout_from_string() and av_channel_layout_describe() now 
>> support
>> a "designation@name" syntax, effectively making both functions reciprocal
>> when there are custom names in some or all channels.
>> It's the syntax suggested by Marton and is both extensible if required 
>> and
>> not too ulgy in human readable output if the string is printed verbatim.
>>
>> *av_channel_layout_index_from_string() and
>> av_channel_layout_channel_from_string() also support this syntax now.
> 
> I have two suggestions. None of them is actually blocking, but since 
> they concern public syntax and API it might be better to decide now.
> 
> av_channel_layout_index_from_string() without "@" in the string matches 
> both builtin names (designations) and custom names. I suggest for it to 
> only match builtin names. If a user wants to match by custom name, 
> "@name" may be specified without a designation. This keeps the two 
> namespaces separate.

Ok, look into implementing this.

> 
> av_channel_layout_channel_from_string() is an API which is not used in 
> the codebase. I am not enterely sure about its purpose, so maybe it 
> should be removed for now, and only added later, if some code actually 
> needs it.

Since you can set custom names and query them without the designation, 
it can be useful as a shortcut for "idx = 
av_channel_layout_index_from_string(str) && 
av_channel_layout_channel_from_index(idx)".
If there were no custom names then yeah, there would be no point to it.

> 
> Thanks,
> Marton
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