[mythtv] [PATCH] Add AFD support for aspect 'magic'

[Stuart Auchterlonie]

On Sat, Jun 04, 2005 at 03:16:03PM +0100, Neale Swinnerton wrote:
> The Active Format Descriptor (AFD) is set by some broadcasters like ITV1
> and CH4 in the UK in their DVB-T streams. This signals what the format
> of the video is, and along with the aspect ratio of the video stream and
> your display it can resize the video 'better'.
> 
> This patch adds support for this to myth. To enable it go to
> Utilities/Setup->Settings->TV Settings->Playback and set aspect override
> to AFD.
> 
> When playing back streams that have AFD set you should see the image
> scaled better. ie. it will apply letterboxing/pillarboxing as
> appropriate, Shoot & Protect areas should be honoured.
> 
> AFD has some caveats:
> 	+ Only works where the MPEG Stream is either 4:3 or 16:9
> 	+ Only works where your display is either 4:3 or 16:9
> 
> Note that if you don't have GuiSizeForTv set the aspect ratio comes from
> the DisplaySize option in your xorg.conf, if GuiSizeForTv is set myth
> calculates the aspect ratio of your screen with the following code
> 
> void VideoOutputXv::InitDisplayMeasurements(uint width, uint height)
> {
>  <SNIP/>
>         int w = DisplayWidth(XJ_disp, XJ_screen_num);
>         int h = DisplayHeight(XJ_disp, XJ_screen_num);
>         int gui_w = w, gui_h = h;
>         gContext->GetResolutionSetting("Gui", gui_w,  gui_h);
>         if (gui_w)
>             w_mm = w_mm * gui_w / w;
>         if (gui_h)
>             h_mm = h_mm * gui_h / h;
> 
>         display_aspect = (float)w_mm/h_mm;
> <SNIP/>
> }
> 
> w_mm/h_mm is the width/height of your screen in mm as reported by X (ie.
> the values passed via DisplaySize option), for me this means I need a
> gui size of 1024x576 to get my display aspect to 1.78.
> 
> I left debug output switched on in the patch, so you will see what value
> myth is calculating for your aspect ratio....
> 
> TODO: I'm not sure that the size calculations for the various
> combinations are correct, it seems to work for my limited testing on
> ITV1 / Ch 4. I'm trying to find a test stream to test this out.

I've just had a look at Farscape that was just recorded off BBC3.
It is always a 4:3 picture trasmitted in 16:9 so I figured they
might have stuck an AFD on it.

The lead in 60 seconds is 16:9 proper so we start off with

XJ aspect 1.77778
Display aspect 1.26199
AFD 0
Before: 1280x1024+0+0
VideoOutput::MoveResize:
Img(0,0 720,576)
Disp(0,148 1280,727)
Offset(0,0)
Vscan(0.000000, 0.000000)
DisplayAspect: 1.261993
VideoAspect(1.777778)
XJ_aspect(1.777778)
CDisplayAspect: 1.261993
Letterbox: 7

Then when the program starts I would expect that the AFD would change
to 9 (from the table below) but it doesn't. We get this..

XJ aspect 1.77778
Display aspect 1.26199
AFD 0
Before: 1280x1024+0+0
VideoOutput::MoveResize:
Img(0,0 720,576)
Disp(0,148 1280,727)
Offset(0,0)
Vscan(0.000000, 0.000000)
DisplayAspect: 1.261993
VideoAspect(1.777778)
XJ_aspect(1.777778)
CDisplayAspect: 1.261993
Letterbox: 7

which is identical to before. Then if I cycle through the various
aspect ratios I get the following...

XJ aspect 1.77778
Display aspect 1.26199
AFD 9
Before: 1280x1024+0+0
VideoOutput::MoveResize:
Img(0,0 720,576)
Disp(0,148 1280,727)
Offset(0,0)
Vscan(0.000000, 0.000000)
DisplayAspect: 1.261993
VideoAspect(1.777778)
XJ_aspect(1.777778)
CDisplayAspect: 1.261993
Letterbox: 0

This is on the transition from AFD to OFF in the aspect ratio override.
With a bit more cycling we return to AFD mode with the following

XJ aspect 1.77778
Display aspect 1.26199
AFD 9
Before: 1280x1024+0+0
VideoOutput::MoveResize:
Img(0,0 720,576)
Disp(0,148 1280,727)
Offset(0,0)
Vscan(0.000000, 0.000000)
DisplayAspect: 1.261993
VideoAspect(1.777778)
XJ_aspect(1.777778)
CDisplayAspect: 1.261993
Letterbox: 7

So now the AFD is 9, but still things haven't been stretched out to 4:3.


I'll see what I can work out why it's doing it, but you may have a
better idea off the top of your head.

btw. I don't have a display res setup in the myth database. The output
is just my desktop at 1280x1024


Stuart


> 
> +/* Active Format Description(AFD) is set in DVB Streams.
> + * By considering both the aspect ratio and the AFD it 
> + * is posible to determine how to present the image in the
> + * correct manner. 
> + * See http://www.dtg.org.uk/publications/books/afd.pdf
> + * for the gory details
> + */
> +enum AfdMode {
> +    kAfd_Unset        = 0,
> +    kAfd_Same         = 8,
> +    kAfd_4_3          = 9,
> +    kAfd_16_9         = 10,
> +    kAfd_14_9         = 11,
> +    kAfd_4_3_Sp_14_9  = 13,
> +    kAfd_16_9_Sp_14_9 = 14,
> +    kAfd_Sp_4_3       = 15,
> +    kAfd_END
> +};
> +