Re: [FFmpeg-devel] [PATCH 00/26] Major library version bump

[Marton Balint <cus@passwd.hu>]

On Tue, 24 Jan 2023, Michael Niedermayer wrote:

> On Tue, Jan 24, 2023 at 12:22:52AM +0100, Marton Balint wrote:
>>
>>
>> On Mon, 23 Jan 2023, Anton Khirnov wrote:
>>
>>> Quoting Marton Balint (2023-01-23 23:41:11)
>>>> On Mon, 23 Jan 2023, Anton Khirnov wrote:
>>>>> Quoting Marton Balint (2023-01-21 23:00:52)
>>>>>> AVCodecContext->frame_number should be changed to int64_t. I guess you
>>>>>> could do something similar which was done for buffer_size_t, but that
>>>>>> seems like a lot of extra work and ifdefry for questionable benefit.
>>>>>
>>>>> Not breaking callers seems like a very solid benefit to me.
>>>>
>>>> I am not sure if I see your point, during unstable, you can break callers,
>>>> and I planned to do the change during unstable.
>>>
>>> My understanding of this instability period is that it's mainly for ABI
>>> changes like reordering struct fields and such, you're still not allowed
>>> to arbitrarily break random APIs. The entire point of having deprecation
>>> periods is that callers can prepare in advance and never actually be
>>> broken.
>>
>> If some fields or API is deprecated, then yes, it makes sense. But if no
>> deprecation / replacement API is provided, then how will anybody prepare?
>> For type changes, fields are usually not deprecated. Ifdefs are only used to
>> prepare the changes for the next API bump. For example, buffer_size_t was in
>> the codebase for 2 months only.
>>
>> It is not that big of a deal to make a patch if #ifdefs, I just really don't
>> see the benefit.
>>
>> An actual problem however, is that printf() like functions expect type
>> specifiers, and unlike buffer sizes, there is a good chance the users
>> sometimes print AVCodecContext->frame_number or AVFrame->xxx_picture_number,
>> which will become undefined behaviour. And yes, the compiler will usually
>> warn, but still, type changes can cause silent breakage. But using #define
>> API guards will not fix this, whenever you change the type, code will get
>> broken, I am not sure if anything can be done about it.
>
> if you want to avoid this then, new type, new identifer

Sure, but do we want AVFrame->coded_picture_number64, 
AVFrame->display_picture_number64 and AVCodecContext->frame_number64?

Regards,
Marton
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