[FFmpeg-devel] [PATCH v5 0/4] Explain what "context" means

[Andrew Sayers]

On Fri, May 24, 2024 at 03:50:52AM +0200, Michael Niedermayer wrote:
> On Thu, May 23, 2024 at 09:00:39PM +0100, Andrew Sayers wrote:
<snip>
> > Imagine you wanted to write a system that nudged people to try new codecs.
> > It might say e.g. "you seem to be using H.264, would you like to try H.265?"
> > Implementing that would probably involve a struct like:
> > 
> > struct AVOldNew {
> >   AVClass* old;
> >   AVClass* new;
> > };
> 
> AVClass would describe the internal decoder structures. This would not be
> correct at all in this example.
> Thats like handing a man 2 CAD documents about 2 engines of 2 cars
> 
> If you wanted to suggest to get a tesla instead of a ford. One would have to
> describe the 2 cars and their differences
> thats 2 AVCodecDescriptor maybe

Hmm, yes fair point.  A better example might be a simple linked list:

struct AVClassList {
    AVClass* cur;
    AVClassList* next;
};

Again, that clearly is a struct that begins with AVClass*, but clearly isn't an
AVClass context structure.

I realise it's a bit of an academic distinction, but IMHO these hypotheticals
suggest it's more accurate to define the term "AVClass context structure"
in terms of usage rather than layout.