[pvrusb2] initialization of video_gop_size

[Mike Isely]

On Sun, 22 Jun 2008, Hans Verkuil wrote:

> 
> The ivtv and cx18 drivers set it during driver initialization (after 
> cx2341x_fill_defaults() is called):
> 
>   itv->params.video_gop_size = itv->is_60hz ? 15 : 12;
> 
> But I notice that none of the other drivers using cx2341x do so. I've 
> CCed the cx88-blackbird and cx23885-417 maintainers as well so that 
> they can update their drivers, or at the very least are aware of this.
> 
> The use of a GOP size of 12 is (as I understand it) legal but 
> non-standard. A GOP size of 15 gives you two I-frames per second, 
> similar to the GOP size of 12 for 25 fps formats.
> 
> An additional problem I discovered is that the gop_size isn't updated 
> after you change from e.g. PAL to NTSC or vice versa. I'm thinking that 
> it might be better to have it set to a default of 0, meaning 'use the 
> current TV standard to decide on the appropriate GOP size'. But this 
> requires a minor API change.

Without having looked at the cx2341x module code (I have been far too 
buried in another project right now), could a driver force it to update 
on video standard change by forcing a complete reinitialization of the 
encoder?  Changing the video standard is not something one is going to 
routinely do and when it happens I have to assume that it is going to be 
disruptive regardless - since presumably one of the choices (pre- or 
post-) probably wasn't correct to begin with.  So just reinitializing 
everything in this case should not be out of bounds.


> 
> I'll look at this tomorrow and if I haven't come up with a better idea 
> I'll propose such a change.
> 
> Small fixes to bring cx88, cx23885 and pvrusb2 in line with ivtv/cx18 
> should most likely be OK to get into 2.6.26, but an API change is 
> definitely 2.6.27.

Agree.

  -Mike


-- 

Mike Isely
isely @ pobox (dot) com
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