framerate and deinterlace2

[Julien Isorce]

Hi,

I would like to know why deinterlace2 changes the framerate ? (see gst_deinterlace2_getcaps then gst_fraction_double).

I do not a lot about the deinterlacing methods. But in an interlacing video flux, an odd frame follows an even frame. Using a frame and its previous frame, the result is one deinterlaced frame.
And so why N interlaced frames you got N-1 deinterlaced frames.
Finally there is no reason to change the framerate.
I am sure I am wrong or missing something important but something I got a framerate about 50/1 in the deinterlace2 ouput while the input framerate is 25/1.

Could someone explain this behaviour ?

Maybe it depends  on the method used (deinterlace2 "method" property).

Thx

Sincerely

Julien



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[Sebastian Dröge-7]

Am Freitag, den 05.12.2008, 21:43 +0100 schrieb Julien Isorce:

> Hi,
>
> I would like to know why deinterlace2 changes the framerate ? (see
> gst_deinterlace2_getcaps then gst_fraction_double).
>
> I do not a lot about the deinterlacing methods. But in an interlacing
> video flux, an odd frame follows an even frame. Using a frame and its
> previous frame, the result is one deinterlaced frame.
> And so why N interlaced frames you got N-1 deinterlaced frames.
> Finally there is no reason to change the framerate.
> I am sure I am wrong or missing something important but something I
> got a framerate about 50/1 in the deinterlace2 ouput while the input
> framerate is 25/1.
>
> Could someone explain this behaviour ?
>
> Maybe it depends  on the method used (deinterlace2 "method" property).

It doesn't depend on the deinterlacing method (but some produce a
jumping picture if outputting the doubled framerate).

The fields property can be used for this, if it's set to all you will
get the doubled framerate, top/bottom will only output the interpolated
top or bottom field.

Let's assume you have a interlaced video (with both fields weaved into
one frame) with 30fps. Taking every even line corresponds to one field,
every odd line corresponds to the other field then. Now these two fields
don't have the exact same timestamp but the second field is 1/2 frame
after the first one, i.e. 1/60 second in our example. The fields=all
deinterlacing will now output a frame every 1/60 seconds, where every
frame is created from the corresponding field and the missing lines are
interpolated by some method (which you can choose with the method
property). This method could of course be to simply take the missing
lines from the previous or following field but there are also some more
complex methods ;)

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[Julien Isorce]

Hi,

Thx for your explanation.

So a video source at 1080i uses as much bandwith as a video source at 1080p.
I believed there was black lines in one interlaced frame and so 1080i was used for lower bandwith.

So I do not understand why 1080i still exist because interlacing was iniatilly used for CRT tv to avoid flickering.
So what are the reasons to use interlace mode in a full numeric chain ? (source, transport, visual)

Then "the NTSC system delivers the rate of 30 frames/s or 60 fields/s", so using deinterlace2, I will get a 60 FPS if fields property is "all", and 30 FPS if "bottom or top". So usually a FULL HD Televisons do deinterlacing using only top/bottom ?

What's the most usual deinterlacing method used in FULL HD screens ?

Sincerely

Julien
 

It doesn't depend on the deinterlacing method (but some produce a
jumping picture if outputting the doubled framerate).

The fields property can be used for this, if it's set to all you will
get the doubled framerate, top/bottom will only output the interpolated
top or bottom field.

Let's assume you have a interlaced video (with both fields weaved into
one frame) with 30fps. Taking every even line corresponds to one field,
every odd line corresponds to the other field then. Now these two fields
don't have the exact same timestamp but the second field is 1/2 frame
after the first one, i.e. 1/60 second in our example. The fields=all
deinterlacing will now output a frame every 1/60 seconds, where every
frame is created from the corresponding field and the missing lines are
interpolated by some method (which you can choose with the method
property). This method could of course be to simply take the missing
lines from the previous or following field but there are also some more
complex methods ;)

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[Cameron Gorrie-2]

> So I do not understand why 1080i still exist because interlacing was
> iniatilly used for CRT tv to avoid flickering.
There are a number of people whose argument is that having motion
captured twice as fast makes things like sporting events easier to
watch, and this is done without increasing bandwidth requirements. My
personal opinion is that I've had enough hours editing videos and
developing applications to feel like I've wasted a significant amount
of my life because of interlaced videos. Apologies for this tangent,
in any case.

Cameron

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[Brian Crowell-2]

2008/12/6 Julien Isorce <[hidden email]>:
> So a video source at 1080i uses as much bandwith as a video source at 1080p.
> I believed there was black lines in one interlaced frame and so 1080i was
> used for lower bandwith.

A video source running at 1080i @ 30 frames per second (that is, 60
fields per second) uses exactly half the bandwidth as 1080p @ 60
frames per second.

To the end viewer, they appear equally fluid, because they both
*appear* to be running at 60 frames per second. The non-interlaced
format will provide twice the vertical detail but will use twice the
bandwidth.

There are no blank lines when interlaced video is transmitted
digitally. Two adjacent fields in a 1080i picture, each measuring
1920x540 pixels, are combined to form a single frame measuring
1920x1080 pixels, where the even-numbered horizontal lines form one
field and the odd-numbered horizontal lines form another. The same
concept applies to standard-definition 480i video.


> So I do not understand why 1080i still exist because interlacing was
> iniatilly used for CRT tv to avoid flickering.
> So what are the reasons to use interlace mode in a full numeric chain ?
> (source, transport, visual)

I think it had to do with the fact that many early HDTVs were
CRT-based. Bandwidth requirements may have come into it.


> What's the most usual deinterlacing method used in FULL HD screens ?

Probably line doubling.

--Brian

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[Julien Isorce]

Hi,

Thx for those informations.

A video source running at 1080i @ 30 frames per second (that is, 60
fields per second) uses exactly half the bandwidth as 1080p @ 60
frames per second.

To the end viewer, they appear equally fluid, because they both
*appear* to be running at 60 frames per second. The non-interlaced
format will provide twice the vertical detail but will use twice the
bandwidth.

There are no blank lines when interlaced video is transmitted
digitally. Two adjacent fields in a 1080i picture, each measuring
1920x540 pixels, are combined to form a single frame measuring
1920x1080 pixels, where the even-numbered horizontal lines form one
field and the odd-numbered horizontal lines form another. The same
concept applies to standard-definition 480i video.

> So I do not understand why 1080i still exist because interlacing was
> iniatilly used for CRT tv to avoid flickering.
> So what are the reasons to use interlace mode in a full numeric chain ?
> (source, transport, visual)

I think it had to do with the fact that many early HDTVs were
CRT-based. Bandwidth requirements may have come into it.

> What's the most usual deinterlacing method used in FULL HD screens ?

Probably line doubling.

--Brian

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