do I have a field order problem ?

[davexnet]

Hello all,
I captured the same thing twice from my Hi-8 camera using two difference mjpeg codecs.
The first, (16 MB) is from STOIK capture with Picvideo mjpeg codec.
The second (13 MB) is in Virtualdub using the the mjpeg codec in FFDshow. Also this clip is captured
in a second XP SP3 on the same box.

When I pay them back, the first clip looks really odd on the text and it reminds of a field order
problem. I've looked at them frame by frame in Virtualdub and I'm unable to confirm it.
The anomaly shows up whether the clips are played back in mpc-hc or WMP - I though they dealt
with interlaced footage on the fly ?

I've included 4 seconds of video from each:
clip 1 http://www.mediafire.com/download.php?z0mie0tatkmh15t
clip 2 http://www.mediafire.com/download.php?2e3hv6q9oqfjxs4

Thanks for any info.

[lordsmurf]

It's hard to tell without playing on a TV.

[jagabo]

I haven't seen the clips yet but you probably don't have a field order problem. I bet you have a field location problem where the top field is stored below (rather than above) the bottom field in the frame.

<later>

Nope. They're both normal interlaced, top field first. One does have a few dropped frames though.

Ffdshow doesn't seem to have it, but many MJPEG decoders have a "field swap" option (this is not a field order option). If you are using one of those make sure you don't have the feature enabled. It will turn this:


into this:

[davexnet]

Thanks for the info. I'll take a look for the option. The other thing that occurred to me is that the capture video card
on each of the XP systems have a difference version of the driver installed. I suspected there may have been some dropped frames;
it's right at the beginning of the clip. The odd thing is, neither of the capturing software I used reported any.

jagabo, I did see the distortion in mpc-hc as in your lower picture in the 16MB clip but not in the other.
I logged onto my Linux box and both played normally in in smplayer.

As long as I can process the clip OK (either mpeg-2 DVD or short WMV project in Windows Movie Maker)
it'll be fine.

[jagabo]

PicVideo's MJPEG codec has the field swap option.

[davexnet]

OK - sounds as if you're advising me to recapture with the option switched. I'll look at it a little closer this time.
I'm still not sure I understand the problem. In your post above you first surmised that there may be a
field location problem, then you said they're both normal interlaced. But clearly, under certain situations, they behave
differently, the 16 MB clip (and the 5 minute clip it was taken from) do produce the image in the lower picture when
played back in WMP (at least on my PC). When I look at them in Virtualdub, I don't see it.

[jagabo]

When I view your two clips on my computer they are the same (in terms of field order and field placement). I can create the problem you seem to be seeing by switching the location of the top and bottom fields (the sample image I posted).

If you are having that problem all you need to do is use the field swap option of the decoder while editing (VirtualDub also has a filter that does it -- field swap). The problem I foresee is that, if you have one MJPEG video with the problem and anotherMJPEG video without it, you can't edit them at the same time -- one or the other will always be wrong (because the same MJPEG decoder will be used by both). You'll have to convert one of the videos before you can edit the two together.

[davexnet]

Thanks for the further info. I rendered the video (16MB clip) in the Graph Edit program and I see that the Microsoft mjpeg decoder
is being used. I press play and see the problem. I get the MS encoder out of the graph and insert the Picvideo decoder
and now the image is fine. Opening the properties show "swap fields" is not selected, and selecting it reveals the problem.

However, if I render the 13 MB clip in Graph Edit using picvideo, the picture looks good regardless of the swap fields setting.
Likewise, it looks fine in the MS codec also.

I'm going to logon to my other XP and see what happens there.

Edit - I think I narrowed it down to the use of the MS decoder.
If I use the FFdshow or Picivdeo, problem doesn't occur. I'm going to modify the "merit" so that the
MS filter is not used.

[jagabo]

Does the MS decoder have a swap fields option?

[davexnet]

No it does not. Still, I'm wondering if there is something non-standard about the way the picvideo
encoder created it's file that confuses the MS filter. It's a pretty old release of picvideo (probably about time I looked
into updating it). ON the other hand, the MS filter has no issues with the content created by the FFDshow mjpeg encoder.