Is this interlacing?

[bigmick]

Hey Guys,

Need a bit of help trying to cap some PAL tennis tapes. They're probably worst case source material - long play, ball sports, bad original reception, 6-8 years old. I know the results aren't going to be great, but the main problem I've got is I'm getting double-images in the fast moving parts - there's two balls flying around the court!

I've attached a screenshot showing what I mean - it's a single frame and before anyone gets funny - I know that's not tennis :) So I don't wear out my tennis tapes I'm experimenting with a cricket tape.

I suspect this is interlacing, but I've tried all sorts of deinterlacing and I can't get rid of the effect and it doesn't look right even played back on a TV (off a media PC) so I'm confused??

My final intended format is (interlaced) DVD. Would love some advice, not only on why I have this double image thing going on, but also on any overall tips for my source material:

long play - is there anything special I need to do because of this?
ball sports - above all I need to make sure I don't lose clarity of the ball - has to remain easy to see

Cheers,
Mick

[LoRd_MuldeR]

You better abuse http://imageshack.us (or a similar service) to post pictures here.
This way you don't need to wait for approval ;)

Also a lot of info and samples about (de)interlacing can be found on this site:
http://100fps.com

[bigmick]

Thanks for the tip on the images, I didn't even notice...it's strict here eh!

That's a great link. Judging by the pics there I'm fairly sure it is interlacing that I'm seeing, but what I don't understand is why when I play it, it doesn't play back smoothly like off the tape - I still see two balls etc. I'm playing it back on a tv off a media pc - unfortunately I don't have a stand-alone dvd player anymore to try it out on that, but all the digital tv I record plays back fine. What could be going on?

Just to get clear in my mind what is going on, please correct me where I get this wrong:

The tape is recorded at 25fps and when played back, the VCR outputs a 50Hz signal that is basically half the information from frame 1 (odd lines) followed by the other half of the information from frame 1 (even lines) then half the information from frame 2 and so on. The TV draws this out on the screen in alternate lines and all is well.

Now, I'm capturing the 25fps and when I open the file up in VirtualDub-Mpeg and look at a single frame I can see the two balls because the single frame really contains two points in time (drawn on alternate lines). Two balls is actually what I should be expecting to see.

But when I play it on the media center, I know my video card is outputing a 50Hz signal to the tv, but something is going wrong in the construction of this signal, but only for the files I have captured...

[LoRd_MuldeR]

The video on the tape is 50 fields (half-frames) per second. For a classical Tube TV this is fine, as it displays 50 fields per second too. PC Monitors of all kind and new TV Screens (LCD, Plasma, etc.) cannot display interlaced properly, because they work progressive (they only display full frames). In the captured video there are still 50 fields per second, but they have been saved as 25 frames per second. Hence: In every frame there are two fields. That's why the even and the odd lines of those frames don't match and show those "combing" artifacts on all moving objects. Now "deinterlacing" is the process that restores full frames from the interlaced video, so it can be displayed properly on PC Screen or LCD/Plasma TV. Basically the deinterlacer can either produce a 25 fps progressive signal (motion information is lost) or a 50 fps signal (bobbing). It's your decision what you want to do. But if you are going to display the video on a TV Screen anyway, you won't have to deinterlace at all!

[Chainmax]

I suggest you to read Decomb's (http://www.neuron2.net/decomb/decombnew.html) readmes and tutorials, the IVTC tutorial (http://www.doom9.org/ivtc-tut.htm) and the capture guide (http://forum.doom9.org/showthread.php?t=78797). They have loads of very useful information about this subject. By the way, if you intend to keep it interlaced (which is the best idea for fast moving interlaced content), you should probably bob, filter and then reinterlace.

[communist]

Hehe its from the Cricket World Cup 2007;)
Anyway if you got pure PAL or NTSC then you wont have to bother with IVTC/Decomb etc.
The only thing you need to be aware of is that your processing chain should account for interlaced material. In other words, you need to capture both fields, if you process/filter the captured footage you will need to filter them 'separately' and last but not least when encoding to MPEG (for DVD) you will need to tell your encoder that the input material is interlaced.

If you media PC is doing anything to the fields then of course it wont look right on TV either. For testing encode a short sample to DVD and play that off a DVD player.

[bigmick]

Cheers guys - thanks for the replies.
I'll experiment a bit more with the deinterlacing. I made a few attempts using a variety of the deinterlacers in VirtualDub-Mpeg, but I couldn't get any results where the ball would move smoothly. I wish I had something reliable to play it back on though as it really adds confusion when you don't know what you are doing and can't be sure if what you are seeing is due to your material or the way it's playing back! Unfortunately I've got no standalone dvd player anymore...

My goal is to preserve the fluidity of motion above all else, so I was thinking I'd leave it interlaced, but given what you say about the LCD TVs not handling that too well, am I making the right move? - my CRT's days are numbered after all.... If I bob the output and get 50fps would that be a better way to go?

[LoRd_MuldeR]

If I bob the output and get 50fps would that be a better way to go?

Bobbing preserves all motion, which might look better. But you get the double number of frames, so it will be harder to encode. Assume about twice the filesize for a 50 fps video, compared to a 25 fps video of the same quality.

VirtualDub doesn't contain very good deinterlacers! There are some external Deinterlacers available for VirtualDub, but I recommend you give Avidemux (http://www.razorbyte.com.au/avidemux/2.4/SVN/3040/avidemux_2.4_r3040_win32.exe) a try. In Avidemux try either "Yadif" (second mode) or "DGBob" (second mode) for bobbing :cool:

[Chainmax]

I'd rather recommend LeakKernelDeint or, even better yet, TDeint+TMM than DGBob.