On Tue, 4 Oct 2022, Anton Khirnov wrote:
Quoting Marton Balint (2022-09-28 21:54:11)
On Wed, 28 Sep 2022, Anton Khirnov wrote:
AVFrame.time_base has been added recently, but is currently not used for
anything. Prepare for its use in encoders by rejecting frames where
time_base is set, but differs from the AVCodecContext one.
How is that not an API break? Users can encode AVFrames with anything in
the AVFrame->time_base right now, if you change that behaviour, that will
surely break some code. That is why it was explicitly documented that
it will be ignored by encoders by default.
Why would there be anything in that field? No code we have currently
sets that field or does anything with it.
It is a public field which was explicitly documented to be ignored by
filters or encoders. The user could store any data in it, because the
documentation of the field ensured it will not be a problem.
If you read back the old threads which added AVFrame->time_base
you will find the reasoning behind the original comments, in fact,
you suggested the actual wording for the documentation of the field, and
now you want now to change the semantics of the field which contradicts
the existing documentation... Usually we introduce a new field and
deprecate the old if we want to do something like this.
One could argue that this break is "small" enough, to not dance around it,
but I don't really see the benefit of the change in the first place. So
the real question is why do you want to start using AVFrame->time_base in
encoders, and what is the feature which is undoable with the current
AVCodecContext->time_base?
Thanks,
Marton
There is no valid reason for
the users to be setting it on the frames they send to lavc.
As for "it would have worked before', there are many precedents where
some nonsensical parameter combination would "work", but then we'd add a
check and it would start returning errors. Callers should not be setting
random fields to random values and expect things to work.
Would applying this patch after a major bump alleviate your concerns? We
wanted to have one for a few months already.
--
Anton Khirnov
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