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| sebdubois |
| Posted: Mar 14 2003, 02:41 PM |
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Hi all,
can someone give me information on the AVI encapsulation format used by Virtualdub, because i have problems understanding some parts of the file structure (especially the end).
Thanks for your answers. |
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| DeXT |
| Posted: Mar 16 2003, 07:10 PM |
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Wotsit.org has a database of file formats, including AVI.
Also do a search in Google for "OpenDML" as it's the extended AVI format that VirtualDub supports.
DeXT
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| sebdubois |
| Posted: Mar 17 2003, 10:54 AM |
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Oh, sorry, I misinterpreted the index structure  , I've got it right now,
Thanks
But I still have a question left,
what are the JUNK chunks for?
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| Kippesoep |
| Posted: Mar 17 2003, 05:57 PM |
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Moderator of the Virtualdub support forum
Group: Moderators
Posts: 447
Member No.: 441
Joined: 6-October 02
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They are used to align data (for instance: to speed up reading from CD-ROMs which use 2048-byte sectors... sector-aligning the data will be a performance improvement). Applications reading AVI files should ignore them and there's no need to write them out. |
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| phaeron |
| Posted: Mar 18 2003, 03:52 AM |
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Virtualdub Developer
Group: Administrator
Posts: 7773
Member No.: 61
Joined: 30-July 02
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JUNK chunks are necessary in a few places. The Microsoft "DV in AVI" doc recommends you use them to pad the LIST/movi chunk to a 2K boundary, and they can be used to disable chunks that must be at the beginning of the file but turn out to be unnecessary once you have finished writing the entire video. VirtualDub also uses them during video capture to avoid having to do unaligned memory copies to the write buffer.
IIRC, parsers can be a bit touchy about where you place such padding chunks. I think some parsers break if you place them between the LIST/avih and LIST/movi blocks.
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| sebdubois |
| Posted: Mar 18 2003, 08:21 AM |
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Thanks for your answers, I think I can get rid of them for my applications.
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