[FFmpeg-devel] [PATCH 001/279] Add a new channel layout API

[Lynne]

8 Dec 2021, 11:06 by cus at passwd.hu:

>
>
> On Wed, 8 Dec 2021, Lynne wrote:
>
>> 8 Dec 2021, 10:22 by h.leppkes at gmail.com:
>>
>>> On Wed, Dec 8, 2021 at 10:14 AM Lynne <dev at lynne.ee> wrote:
>>>
>>>>
>>>> 8 Dec 2021, 02:06 by jamrial at gmail.com:
>>>>
>>>>>
>>>>> +enum AVChannel {
>>>>> +    ///< Invalid channel index
>>>>> +    AV_CHAN_NONE = -1,
>>>>> +    AV_CHAN_FRONT_LEFT,
>>>>>
>>>>
>>>> No, not the pixfmt mistake again. Set AV_CHAN_NONE to 0,
>>>> the rest can follow. Or keep AV_CHAN_NONE to -1
>>>> and add a new AV_CHAN_UNSPECIFIED as 0.
>>>>
>>>
>>> Care to elaborate on the reasons of this opinion? Using -1 as invalid
>>> and 0...x as valid entries seems quite reasonable to me.
>>>
>>
>> Zero-initialization. I've had issues in the past telling
>> YUV420P from <uninitialized>.
>>
>
> It is convenient to be able to set the channel layout mask by a simple byte shift of the ID-s.
>
> AV_CH_FRONT_LEFT = 1 << AV_CHAN_FRONT_LEFT.
>
> So I'd say that is the reason that it is designed that way, because this way existing channel layout masks can be kept without breaking ABI.
>

Those can be set with offsets, e.g.
AV_CH_FRONT_LEFT = 1 << (AV_CHAN_FRONT_LEFT - 2).

I'd like to not have weird values in enums because the old
API, just being deprecated, must have its way and can't deal
with an offset.