[linux-dvb] Re: [PATCH] new video event and ioctl

[Johannes Stezenbach <js@convergence.de>]

Felix Domke wrote:
> Johannes Stezenbach wrote:
> 
> >The V4 API has:
> >
> >   unsigned int frame_rate; /* in frames per 1000sec */
> > 
> >
> I'm against this.
> 
> The reason is that arbitrary framerates are not allowed in MPEG-2 
> (correct me if i'm wrong, i'm currently too lazy to read 13818-2 
> again...), and there's no hardware being able to playback this simply 
> because there's no TV standard for arbitrary framrates.
> 
> I use the framerate to decide wheter to have a PAL or NTSC stream, or 
> better: if the stream is more likely to comply with the NTSC standard or 
> the PAL standard (or in future any HDTV standard). I think handling the 
> "odd" framerates (23.976 etc.) is hard enough - what is the application 
> expect to do if the framerate becomes, for example, 31337? (switching to 
> eTSC?) Dropping frames and do simple NTSC?
> Seriously, are there are really real-world-cases where the enum proposed 
> by Andreas isn't enough? I really would like to restrict us here to the 
> real-world framerates, since only this will give you the possibility to 
> handle all values correctly.
> 
> After all, we don't want to insert any "frame rate drift" etc. here, 
> since that's not what the value should say. It should only give a hint 
> wheter to display the source in NTSC or PAL and maybe some informational 
> output.
> 
> (Of course if someone tells me that arbitrary framerates are of any(!) 
> use, i'll change my position here, but after all, it's a DVB-API, not a 
> generic stream playback API. MPEG was restricted to a set of discret 
> frame rates, because it's simply impossible to build a decoder which 
> supports all frame rates without doing complex pullup/downs).

DVB has TV oriented requirements (i.e. frame rate matching PAL
or NTSC), but MPEG-2 can also be used for special purpose stuff
like CCTV or info terminals (used in public places like museums),
where low frame rates are sufficient.

Also, newer STB/DVD chips might support MPEG-4 or other codecs,
and you cannot predict what frame rates you have to deal with.
But of course no one expects a STB to play back everything flawlessly,
it's just that IMHO the DVB API should allow for some non-DVB
extensions.


Regards,
Johannes


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