[FFmpeg-soc] [PATCH] rtsp tunneling

[Martin Storsjö]

On Wed, 16 Jun 2010, Michael Niedermayer wrote:

> On Wed, Jun 16, 2010 at 07:51:32PM +0300, Martin Storsjö wrote:
> > On Wed, 16 Jun 2010, Michael Niedermayer wrote:
> > 
> > > On Mon, Jun 14, 2010 at 08:12:30PM +0300, Martin Storsjö wrote:
> > > > 
> > > > Additionally, as far as I've understood AVOptions, they can only set 
> > > > something within one struct, since it simply uses offsets. For this case, 
> > > > we'd need AVOptions that would only apply if the URLContext happens to be 
> > > > a HTTP context, and then set the options within the priv_data, which can't 
> > > > be done as a simple offset (unless the priv_data is tacked on at the 
> > > > end of the context...)
> > > 
> > > I think we should check the past discussion about using AVOptions and private
> > > contexts. but from memory
> > > Adding an AVClass pointer to URLProtocol (and a priv_data_size of course too)
> > > allows us to allocate and init to defaults the private context in generic code
> > 
> > Not as far as I understand it. In libavcodec/opt.c, for example 
> > av_set_number2, lines 63-70, store values using this logic:
> > 
> >     dst= ((uint8_t*)obj) + o->offset;
> >     *(int*)dst= llrint(num/den)*intnum;
> > 
> > So the only things it can express are storing values with a plain offset 
> > from the start of the object. There's no code for dereferencing the 
> > priv_data pointer and using that as an object.
> > 
> > In order to set values within the private data, we'd need to make the 
> > private data an AVClass so that it can have different options depending on 
> > what the actual protocol is. Then in the generic AVClass for URLContext, 
> > we'd need to store the offset of the private data pointer, so that the 
> > generic AVOption code can check for options in the private data if the 
> > option wasn't found in the generic URLContext.
> 
> The user code that calls av_set_number2() can just check if it failed and
> callit on priv_data
> not saying this is better, iam just saying that the extension you hint at is
> not strictly needed

Hmm, true, that would perhaps simplify things a bit. But even then, we'd 
need a way to know whether priv_data actually contains an AVClass or not. 
Either we'd mandate such a member for all protocols' priv_data, or add 
some flag somewhere in URLContext, e.g. priv_data_has_class.

// Martin