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

[Marton Balint]

On Wed, 8 Dec 2021, Lynne wrote:

> 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).

Well, I find this less fortunate then the need to initialize NONE to -1...

> 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.

AV_CH_FRONT_LEFT and similar is not deprecated, these are still used for 
the native channel order which is still using a mask.

Regards,
Marton