Using Blender 2.72a, I rendered an H.264 AVI. I had issues opening it in Lightworks. Here is a response from Lightworks support after reading an attachment from MediaInfo.
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A new reply has been posted on the Lightworks Forum
Message Subject : Re: Lightworks 12 not reading frame rate correctly
Category : Bugs
Posted by : jwrl
URL : http://www.lwks.com/index.php?option=com_kunena&func=view&catid=14&id=81943&Itemid=81#81945
Message :
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Blender has output a variable frame rate AVI file - which I find surprising. It should be reported to the Blender foundation as a bug.
That said, you can still convert that file to import into Lightworks. You will find EyeFrame here (http://www.lwks.com/index.php?option=com_kunena&func=view&catid=23&id=30817&Itemid=81). It was created by a Lightworks user, tin2tin, for just this sort of problem.
As an alternative, there's also ClipToolz Convert (http://www.cliptoolz.com/convert.html). It's under active development, and its developer is a user here too. It will also give you a constant frame rate file.
As another alternative you could possibly use Handbrake to do the same thing, although I've never been terribly happy with it.
For what it's worth, I use TIFF, TGA or PNG sequences when exporting from Blender. Frame rate isn't an issue, and it's much simpler to repair a small section of an exported sequence should you need to.
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I don't know if this is a bug or not, but Lightworks suggested I report this to you. I have attached my system info and the media info from the AVI.
Thanks
William{F121044}
{F121045}