[FFmpeg-soc] [PATCH] rtsp tunneling

[Michael Niedermayer]

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

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Frequently ignored awnser#1 FFmpeg bugs should be sent to our bugtracker. User
questions about the command line tools should be sent to the ffmpeg-user ML.
And questions about how to use libav* should be sent to the libav-user ML.
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