Grabbing 4:3 and 16:9

Grabbing 4:3 and 16:9

[Michel Bardiaux]

Our current systems use Hauppauge WinTV, dmesg as follows:

bttv1: Bt878 (rev 17) at 01:08.0, irq: 17, latency: 64, mmio: 0xf8001000
bttv1: detected: Hauppauge WinTV [card=10], PCI subsystem ID is 0070:13eb
bttv1: using: Hauppauge (bt878) [card=10,autodetected]
bttv1: Hauppauge/Voodoo msp34xx: reset line init [5]
tuner: chip found @ 0xc2
i2c-core.o: client [(tuner unset)] registered to adapter [bt848 #1](pos. 0).
i2c-core.o: adapter bt848 #1 registered as adapter 1.
bttv1: Hauppauge eeprom: model=44806, tuner=Temic 4046FM5 (22), radio=no
bttv1: using tuner=22
tuner: type set to 22 (Temic PAL/SECAM multi (4046 FM5))
bttv1: i2c: checking for MSP34xx @ 0x80... not found
bttv1: i2c: checking for TDA9875 @ 0xb0... not found
bttv1: i2c: checking for TDA7432 @ 0x8a... not found
bttv1: PLL: 28636363 => 35468950 .. ok
bttv1: registered device video1
bttv1: registered device vbi1

Here in Belgium the broadcasts is sometimes 4:3, sometimes 16:9. 
Currently, the card goes automatically in letterbox mode when it 
receives 16:9, and our software captures the 4:3 frames at size 704x576. 
What I would like to do is to capture the 16:9 broadcast without 
letterboxing (and the 4:3 without horizontal padding!) simply by 
changing the pixel aspect ratio stated in our MPEG files. And since we 
do 24/7 captures, this has to be done on-the-fly, no reinitialization of 
the cards or the software allowed. Which leads to 2 questions:

1. How do I sense from the software that the mode is currently 16:9 or 4:3?

2. How do I setup the bttv so that it does variable anamorphosis instead 
of letterboxing? If that is at all possible of course...

I *am* googling for all that, but "16/9" is one of those queries on 
which search engines are really really bad, like "date" or "thread" :-(

TIA,
-- 
Michel Bardiaux
R&D Director
T +32 [0] 2 790 29 41
F +32 [0] 2 790 29 02
E mailto:mbardiaux@mediaxim.be

Mediaxim NV/SA
Vorstlaan 191 Boulevard du Souverain
Brussel 1160 Bruxelles
http://www.mediaxim.com/

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Re: Grabbing 4:3 and 16:9

[Daniel Glöckner]

On Tue, Feb 26, 2008 at 12:19:39PM +0100, Michel Bardiaux wrote:
> Here in Belgium the broadcasts is sometimes 4:3, sometimes 16:9. 
> Currently, the card goes automatically in letterbox mode when it 
> receives 16:9, and our software captures the 4:3 frames at size 704x576. 

The card does not go into letterbox mode. It's the broadcaster who
squeezes the 16:9 picture into 432 lines surrounded by 144 black lines.
Some fill the chroma part of the black lines with a PALPlus helper
signal. Although the algorithms to decode PALPlus are well documented in
ETS 300 731, I have never seen a software implementation.

> 1. How do I sense from the software that the mode is currently 16:9 or 4:3?

Some broadcasters use WSS to signal 16:9.
In Germany some signal 4:3 even on 16:9 shows.
Read ETSI EN 300 294.

> 2. How do I setup the bttv so that it does variable anamorphosis instead 
> of letterboxing? If that is at all possible of course...

You can't. Bttv can't stretch vertically.

  Daniel

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Re: Grabbing 4:3 and 16:9

[Alan Cox]

On Tue, Feb 26, 2008 at 02:02:00PM +0100, Daniel Glöckner wrote:
> > 2. How do I setup the bttv so that it does variable anamorphosis instead 
> > of letterboxing? If that is at all possible of course...
> 
> You can't. Bttv can't stretch vertically.

Use an OpenGL texture is probably the easiest for that kind of effect.

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Re: Grabbing 4:3 and 16:9

[Michel Bardiaux]

Alan Cox wrote:
> On Tue, Feb 26, 2008 at 02:02:00PM +0100, Daniel Glöckner wrote:
>>> 2. How do I setup the bttv so that it does variable anamorphosis instead 
>>> of letterboxing? If that is at all possible of course...
>> You can't. Bttv can't stretch vertically.
> 
> Use an OpenGL texture is probably the easiest for that kind of effect.

I didnt want the stretch per se, but to avoid losing info because of the 
letterboxing (the final project involves reading small print from film 
credits on the captured MPEGs). But Daniel wrote that the 16:9 analog 
broadcasts have only 432 lines, so the info is not there in the first 
place. So that effect isnt an option for me. But thanks anyway.

-- 
Michel Bardiaux
R&D Director
T +32 [0] 2 790 29 41
F +32 [0] 2 790 29 02
E mailto:mbardiaux@mediaxim.be

Mediaxim NV/SA
Vorstlaan 191 Boulevard du Souverain
Brussel 1160 Bruxelles
http://www.mediaxim.com/

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Re: Grabbing 4:3 and 16:9

[Michel Bardiaux]

Daniel Glöckner wrote:
> On Tue, Feb 26, 2008 at 12:19:39PM +0100, Michel Bardiaux wrote:
>> Here in Belgium the broadcasts is sometimes 4:3, sometimes 16:9. 
>> Currently, the card goes automatically in letterbox mode when it 
>> receives 16:9, and our software captures the 4:3 frames at size 704x576. 
> 
> The card does not go into letterbox mode. It's the broadcaster who
> squeezes the 16:9 picture into 432 lines surrounded by 144 black lines.

Let me rephrase to check I understood correctly. In analog TV, there are 
no anamorphic broadcasts. When the WSS (accessible via /dev/vbi, right?) 
states 16:9, then a 16:9 (sic) TV switches to a mode where it crops 2x72 
lines, then stretches the image both horizontally and vertically to fill 
the whole 16:9 screen. Am I correct?

I must admit I have difficulty believing that. Could you give me the 
URLs of sites explaining all that?

> Some fill the chroma part of the black lines with a PALPlus helper
> signal. Although the algorithms to decode PALPlus are well documented in
> ETS 300 731, I have never seen a software implementation.
> 
>> 1. How do I sense from the software that the mode is currently 16:9 or 4:3?
> 
> Some broadcasters use WSS to signal 16:9.
> In Germany some signal 4:3 even on 16:9 shows.
> Read ETSI EN 300 294.
> 
>> 2. How do I setup the bttv so that it does variable anamorphosis instead 
>> of letterboxing? If that is at all possible of course...
> 
> You can't. Bttv can't stretch vertically.
> 
>   Daniel


-- 
Michel Bardiaux
R&D Director
T +32 [0] 2 790 29 41
F +32 [0] 2 790 29 02
E mailto:mbardiaux@mediaxim.be

Mediaxim NV/SA
Vorstlaan 191 Boulevard du Souverain
Brussel 1160 Bruxelles
http://www.mediaxim.com/

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Re: Grabbing 4:3 and 16:9

[Alan Cox]

On Tue, Feb 26, 2008 at 05:40:27PM +0100, Michel Bardiaux wrote:
> credits on the captured MPEGs). But Daniel wrote that the 16:9 analog 
> broadcasts have only 432 lines, so the info is not there in the first 
> place. So that effect isnt an option for me. But thanks anyway.

Per frame.... if you sample as it scrolls and line up the title tops I suspect
most of the time you can get more samples as the title moves.

Just a crazy idea

Alan

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Re: Grabbing 4:3 and 16:9

[Michel Bardiaux]

Alan Cox wrote:
> On Tue, Feb 26, 2008 at 05:40:27PM +0100, Michel Bardiaux wrote:
>> credits on the captured MPEGs). But Daniel wrote that the 16:9 analog 
>> broadcasts have only 432 lines, so the info is not there in the first 
>> place. So that effect isnt an option for me. But thanks anyway.
> 
> Per frame.... if you sample as it scrolls and line up the title tops I suspect
> most of the time you can get more samples as the title moves.
> 
Not crazy, I am *also* considering various image enhancement techniques, 
I just want to start from the best possible capture in the first place. 
That means capturing at 768(or more?) wide instead of 704; in YUV422P 
instead of YUV420P; avoiding reizing, and use better resizing 
algorithms. And capturing at 576 instead of 432 vertically would help too.

As I find more relevant pages, my question has now become: given a 
768x576 capture (by a BT878) can I check whether the PALPLUS is there? 
No use trying to implement the decoder in software if the signal simply 
isnt there!

-- 
Michel Bardiaux
R&D Director
T +32 [0] 2 790 29 41
F +32 [0] 2 790 29 02
E mailto:mbardiaux@mediaxim.be

Mediaxim NV/SA
Vorstlaan 191 Boulevard du Souverain
Brussel 1160 Bruxelles
http://www.mediaxim.com/

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Re: Grabbing 4:3 and 16:9

[Hans Verkuil]

On Tuesday 26 February 2008 17:55:53 Michel Bardiaux wrote:
> Daniel Glöckner wrote:
> > On Tue, Feb 26, 2008 at 12:19:39PM +0100, Michel Bardiaux wrote:
> >> Here in Belgium the broadcasts is sometimes 4:3, sometimes 16:9.
> >> Currently, the card goes automatically in letterbox mode when it
> >> receives 16:9, and our software captures the 4:3 frames at size
> >> 704x576.
> >
> > The card does not go into letterbox mode. It's the broadcaster who
> > squeezes the 16:9 picture into 432 lines surrounded by 144 black
> > lines.
>
> Let me rephrase to check I understood correctly. In analog TV, there
> are no anamorphic broadcasts. When the WSS (accessible via /dev/vbi,
> right?) states 16:9, then a 16:9 (sic) TV switches to a mode where it
> crops 2x72 lines, then stretches the image both horizontally and
> vertically to fill the whole 16:9 screen. Am I correct?

Yes, this is really true. Remember that the broadcast should still work 
when received by an old 4:3 TV. The only way to ensure that it still 
looks OK is to letterbox it. As mentioned before PALPlus allows the 
broadcaster to encode additional information encoded in the black bars 
to improve the image quality (never looked into that, though).

BTW, WSS does allow anamorphic broadcasts, although it is very rare. I 
saw it once, but I've always suspected that someone made a 
configuration error because anamorphic broadcasts look squashed on 
normal 4:3 TVs.

> I must admit I have difficulty believing that. Could you give me the
> URLs of sites explaining all that?

http://en.wikipedia.org/wiki/Widescreen_signaling

http://en.wikipedia.org/wiki/PALPlus

Regards,

	Hans

>
> > Some fill the chroma part of the black lines with a PALPlus helper
> > signal. Although the algorithms to decode PALPlus are well
> > documented in ETS 300 731, I have never seen a software
> > implementation.
> >
> >> 1. How do I sense from the software that the mode is currently
> >> 16:9 or 4:3?
> >
> > Some broadcasters use WSS to signal 16:9.
> > In Germany some signal 4:3 even on 16:9 shows.
> > Read ETSI EN 300 294.
> >
> >> 2. How do I setup the bttv so that it does variable anamorphosis
> >> instead of letterboxing? If that is at all possible of course...
> >
> > You can't. Bttv can't stretch vertically.
> >
> >   Daniel



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Re: Grabbing 4:3 and 16:9

[Michel Bardiaux]

Michel Bardiaux wrote:
> Alan Cox wrote:
>> On Tue, Feb 26, 2008 at 05:40:27PM +0100, Michel Bardiaux wrote:
>>> credits on the captured MPEGs). But Daniel wrote that the 16:9 analog 
>>> broadcasts have only 432 lines, so the info is not there in the first 
>>> place. So that effect isnt an option for me. But thanks anyway.
>>
>> Per frame.... if you sample as it scrolls and line up the title tops I 
>> suspect
>> most of the time you can get more samples as the title moves.
>>
> Not crazy, I am *also* considering various image enhancement techniques, 
> I just want to start from the best possible capture in the first place. 
> That means capturing at 768(or more?) wide instead of 704; in YUV422P 
> instead of YUV420P; avoiding reizing, and use better resizing 
> algorithms. And capturing at 576 instead of 432 vertically would help too.
> 
> As I find more relevant pages, my question has now become: given a 
> 768x576 capture (by a BT878) can I check whether the PALPLUS is there? 
> No use trying to implement the decoder in software if the signal simply 
> isnt there!
> 
Explained here:

http://en.wikipedia.org/wiki/Widescreen_signaling

Now how to get at that info? zvbi/libzvbi?

-- 
Michel Bardiaux
R&D Director
T +32 [0] 2 790 29 41
F +32 [0] 2 790 29 02
E mailto:mbardiaux@mediaxim.be

Mediaxim NV/SA
Vorstlaan 191 Boulevard du Souverain
Brussel 1160 Bruxelles
http://www.mediaxim.com/

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Re: Grabbing 4:3 and 16:9

[Alan Cox]

On Tue, Feb 26, 2008 at 06:12:42PM +0100, Michel Bardiaux wrote:
> As I find more relevant pages, my question has now become: given a 
> 768x576 capture (by a BT878) can I check whether the PALPLUS is there? 

I don't know and the manual doesn't seem to answer that. You can certainly
fish out stuff like teletext info  in software that way (and US closed
caption/analog ip over tv)

> No use trying to implement the decoder in software if the signal simply 
> isnt there!

Agreed

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Re: Grabbing 4:3 and 16:9

[Daniel Glöckner]

On Tue, Feb 26, 2008 at 06:12:42PM +0100, Michel Bardiaux wrote:
> As I find more relevant pages, my question has now become: given a 
> 768x576 capture (by a BT878) can I check whether the PALPLUS is there?

WSS is in the first line of the 576 line picture.
One of the bits says if there is PALplus.

WSS standard:
http://webapp.etsi.org/WorkProgram/Report_WorkItem.asp?WKI_ID=16170

PALplus standard:
http://webapp.etsi.org/workprogram/Report_WorkItem.asp?WKI_ID=3850

You can use libzvbi to decode the information:

vbi_raw_decoder_init(&vbi_rd);
vbi_rd.scanning = 625;
vbi_rd.sampling_format = VBI_PIXFMT_YUYV;
vbi_rd.sampling_rate = 13500000.0*width/702;
vbi_rd.offset = 186*width/924;
vbi_rd.bytes_per_line = width*2;
vbi_rd.start[0] = 23;
vbi_rd.count[0] = 1;
vbi_rd.start[1] = 0;
vbi_rd.count[1] = 0;
vbi_rd.interlaced = 0;
vbi_rd.synchronous = 1;
vbi_raw_decoder_add_services(&vbi_rd,VBI_SLICED_WSS_625,0);
while(framebuf=grabpicture()) {
  vbi_sliced sliced;
  if(vbi_raw_decode (&vbi_rd, framebuf, &sliced)
     && sliced.id==VBI_SLICED_WSS_625)
  {
    wss=(sliced.data[1]<<8)+sliced.data[0];
    if(wss&64) {
      /* There is PALplus
      
         I have seen the decoder generate false positives.
	 Check aspect ratio bits for >=16:9 and their odd parity bit
	 to be shure. */
    }
  }
}

  Daniel

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Re: Grabbing 4:3 and 16:9

[Michel Bardiaux]

Hans Verkuil wrote:
> On Tuesday 26 February 2008 17:55:53 Michel Bardiaux wrote:
>> Daniel Glöckner wrote:
>>> On Tue, Feb 26, 2008 at 12:19:39PM +0100, Michel Bardiaux wrote:
>>>> Here in Belgium the broadcasts is sometimes 4:3, sometimes 16:9.
>>>> Currently, the card goes automatically in letterbox mode when it
>>>> receives 16:9, and our software captures the 4:3 frames at size
>>>> 704x576.
>>> The card does not go into letterbox mode. It's the broadcaster who
>>> squeezes the 16:9 picture into 432 lines surrounded by 144 black
>>> lines.
>> Let me rephrase to check I understood correctly. In analog TV, there
>> are no anamorphic broadcasts. When the WSS (accessible via /dev/vbi,
>> right?) states 16:9, then a 16:9 (sic) TV switches to a mode where it
>> crops 2x72 lines, then stretches the image both horizontally and
>> vertically to fill the whole 16:9 screen. Am I correct?
> 
> Yes, this is really true. Remember that the broadcast should still work 
> when received by an old 4:3 TV. The only way to ensure that it still 
> looks OK is to letterbox it. As mentioned before PALPlus allows the 
> broadcaster to encode additional information encoded in the black bars 
> to improve the image quality (never looked into that, though).
> 
> BTW, WSS does allow anamorphic broadcasts, although it is very rare. I 
> saw it once, but I've always suspected that someone made a 
> configuration error because anamorphic broadcasts look squashed on 
> normal 4:3 TVs.
> 
>> I must admit I have difficulty believing that. Could you give me the
>> URLs of sites explaining all that?
> 
> http://en.wikipedia.org/wiki/Widescreen_signaling
> 
> http://en.wikipedia.org/wiki/PALPlus

To summarize: I know now that PALPLUS is indeed widely used in Belgium 
for analog TV (via cable usually); that I can detect it from WSS using 
libzvbi.

But PALPLUS seems to be being deprecated; e.g. the wikipedia pages 
explain it was, but no longer is, used in the Netherlands. Just like 
analog-TV itself. So, unless I can find (any suggestions?) a ready-made 
open-source software decoder for PALPLUS, it is unlikely we will attempt 
to extract that info. Much better to work on digital-TV!

Thanks again to all who helped.

> 
> Regards,
> 
> 	Hans
> 
>>> Some fill the chroma part of the black lines with a PALPlus helper
>>> signal. Although the algorithms to decode PALPlus are well
>>> documented in ETS 300 731, I have never seen a software
>>> implementation.
>>>
>>>> 1. How do I sense from the software that the mode is currently
>>>> 16:9 or 4:3?
>>> Some broadcasters use WSS to signal 16:9.
>>> In Germany some signal 4:3 even on 16:9 shows.
>>> Read ETSI EN 300 294.
>>>
>>>> 2. How do I setup the bttv so that it does variable anamorphosis
>>>> instead of letterboxing? If that is at all possible of course...
>>> You can't. Bttv can't stretch vertically.
>>>
>>>   Daniel

-- 
Michel Bardiaux
R&D Director
T +32 [0] 2 790 29 41
F +32 [0] 2 790 29 02
E mailto:mbardiaux@mediaxim.be

Mediaxim NV/SA
Vorstlaan 191 Boulevard du Souverain
Brussel 1160 Bruxelles
http://www.mediaxim.com/

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