[FFmpeg-devel] [PATCH] Move stream_options to avformat

[wm4]

On Sun, 25 Jan 2015 16:18:53 +0000
Paul B Mahol <onemda at gmail.com> wrote:

> On 1/25/15, wm4 <nfxjfg at googlemail.com> wrote:
> > On Sun, 25 Jan 2015 13:39:10 +0100
> > Michael Niedermayer <michaelni at gmx.at> wrote:
> >
> >> On Sun, Jan 25, 2015 at 01:18:31PM +0100, Michael Niedermayer wrote:
> >> > On Sun, Jan 25, 2015 at 12:15:40PM +0100, Reimar Doeffinger wrote:
> >> > > On 25.01.2015, at 03:08, Michael Niedermayer <michaelni at gmx.at> wrote:
> >> > > > On Sun, Jan 25, 2015 at 02:31:33AM +0100, wm4 wrote:
> >> > > >>
> >> > > >>>>
> >> > > >>>> As an experienced API user, I don't have the slightest clue what
> >> > > >>>> I'd do
> >> > > >>>> with this API, or where to find information about it.
> >> > > >>>
> >> > > >>> the primary goal is to remove duplicated disposition type tables,
> >> > > >>> which needs one of the tables to be public first
> >> > > >>>
> >> > > >>> [...]
> >> > > >>
> >> > > >> And this is the most awkward way you could find to do this?
> >> > > >
> >> > > > No, i could certainly find a more akward way, if people prefer
> >> > > >
> >> > > > this is just the way that would be a big step towards consistent
> >> > > > and simple access to the structs
> >> > > > All public structs use AVClass and AVOptions to allow applications
> >> > > > to extract/enumerate fields except a few like AVStream
> >> > > > this patch would add these AVClass & AVOption for AVStream, its
> >> > > > indeed not populated for all fields and AVStream doesnt have a
> >> > > > AVClass as its first field due to ABI. But its a step toward it
> >> > > >
> >> > > > Would people prefer that each field in AVStream has a custom and
> >> > > > different way to access it, as long as it looks simpler when looked
> >> > > > at in isolation ?
> >> > >
> >> > > Sorry if it's useless of me to only state some obvious questions, but:
> >> > > I think it's clear we all want a simple, obvious and consistent API :)
> >> > > If it's a bit messy, might there be a point in holding off a bit so we
> >> > > aren't stuck with something complicated?
> >> > > Could possibly another approach after a major bump be nicer?
> >> > > Or maybe better documentation/examples?
> >> >
> >> > > I think this started with a valid complaint/concern but unfortunately
> >> > > no better alternative, could we stick to considering that instead of
> >> > > going over to agressive rhethoric?
> >> >
> >> > absolutley
> >> > i would strongly prefer if others could take this over, my interrest
> >> > was just in the technical side and i wanted to move AVStream to
> >> > the same system we use for all other structs. As well as fixing the
> >> > quite valid issue nicolas had raised with the duplicated tables.
> >> > I am quite surprised that others dont see this as a clear and
> >> > uncontroversal step, there really are just
> >> > 1. If we want AVStream to be consistent with other structs, that means
> >> >    AVOption & AVClass. And this patch is a step toward it, one could
> >> >    make a bigger or smaller step but its then either more or less
> >> >    code not different code.
> >> > 2. There could be a different system be used for this field or for
> >> >    AVStream, this would be inconsistent
> >> > 3. We can implement both a system based on AVOptions/AVClass and a
> >> >    system without them, why would this field that noone cared about
> >> >    until now need this, iam not sure though
> >> > 4. We can leave the triplicated tables as is and hope not to forget
> >> >    updating them in sync
> >> >
> >> > To me the best choice is clear, move toward the same system we use
> >> > elsewhere. Change that system everywhere if it could be improved
> >> > I see nothing controversal on this patch but others do apparently.
> >> > As i dont see what issue people have with this, i certainly cannot
> >> > help fixing the patch. But iam happy to review & approve the solution
> >> > that people do prefer
> >>
> >> About the documentation & example side, i dont think this should yet
> >> be used from outside, its only a partial implementation of AVOption
> >> for AVStream, a full implementation needs a ABI bump due to the
> >> first field needing to be a AVClass
> >>
> >> [...]
> >>
> >
> > How is it even consistent with "other structs"? Doesn't it just resolve
> > flags? Resolving flags with a complicated AVOption contraption (which
> > every user has to understand and duplicate) doesn't seem like a good
> > choice to me at all. I hear about API users fighting with the basics of
> > the FFmpeg API because it's so weird and complicated; seeing patches
> > like this just feel like a bad joke in contrast.
> >
> > What's wrong with:
> >
> >     int av_parse_disposition_flags(const char *s);
> >
> > ?
> 
> How than one can know which flags are available?

Well yes, C doesn't have reflection, but I doubt AVOption is a good
replacement for that. But you still could fall back to awkward things
like messing with AVClasses if you really need.