[libav-tools] Realizing VirtualDub's FieldDelay filter in avconv?

Dr. Jochen Blödorn jochen.bloedorn at gmail.com
Tue Jun 11 12:36:12 CEST 2013


Maybe somebody can give me a hint to correct a problem with mpeg2 videos by
applying a filter in avconv.

On some occasions a movie recorded from television has a wrong field order.
It's not the problem of switched top- and bottom field, than rather the
correlation of the fields to the frame is messed up by one field. I'll try
to describe this by a graphic:

In the example frames are separated by „|“ and are named „A...D“, whereby
top fields are represented by „t“, bottom Fields are represented by „b“.

So normally the order should be:
 At Ab | Bt Bb | Ct Cb | Dt Db | ...

In the abnormal case the order is:

At | Ab Bt | Bb Ct | Cb Dt | Db …

Now the consequence is obvious:
1) the video appears interlaced, even if it is progressive
2) if we assume a scene change between frames B and C, we get one frame,
containing mixed images of scene B and scene C ( | Bb Ct | )

 In the past I worked with MS Windows and VirtualDub. The latter provides a
filter called „Field Delay“, wich corrects the problem. So far I wasn't
able, to figure out, how this can be done with avconv. However I'm not very
experienced with avconv, so please be gentle with me.

Tanks in advance

Jochen

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Dr. Jochen Blödorn

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