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§ AVI files and common problems

I thought today I'd actually post some advice that was relevant to desktop video. But first, some commenters to my "I hate Windows" story asked for me to post my port of the Samba 4.x "editreg" tool, so here it is: I've only included the source code because the port is VERY rough and doesn't do full argument passing, and realistically you have to hack it to use it; also, it doesn't actually allow you to edit the registry, only dump its contents. Still, it works. At the time of this writing, you can get the original source code from the official Samba CVS web browser.

Now, about AVI files....

AVI stands for "Audio/Video Interleaved" and holds both audio and video together in a playable format. The basic structure of an AVI file comes from a general file structure called the Resource Interchange File Format (RIFF), which is in turn based off of the Electronic Arts IFF specification that had its roots on the Amiga. RIFF files consist of a series of chunks, each prefixed by a four-character chunk ID and a four-byte length. These chunks may in turn be nested to form a structured file. This chunk structure is nice because any unrecognized chunk can simply be skipped, allowing a file format to be extended without breaking backwards compatibility. The Portable Network Graphics (PNG) standard has an even more evolved tagging system that also encodes "should-copy" and "must-understand" bits so that old programs even have an idea of what they should do with an unrecognized chunk.

Here's what the structure of a sample AVI file looks like:

RIFF 'AVI '            Audio/Video Interleaved file
LIST 'hdrl' Header LIST
'avih' Main AVI header
LIST 'strl' Video stream LIST
'strh' Video stream header
'strf' Video format
LIST 'strl' Audio stream LIST
'strh' Audio stream header
'strf' Audio format
LIST 'movi' Main data LIST
'01wb' Audio data
'00dc' Video frame
'idx1' Index

Some notes:

If you load an AVI file into VirtualDub's hex editor, the Show RIFF Tree (Ctrl+R) command will display the RIFF tree for the file.

Overall, AVI isn't a very complex file format, and in particular it's very easy to write -- so it's not surprising that a lot of programs support it. Often AVI gets a lot of flak for not supporting a lot of newer video storage functionality, such as subtitles, timestamps, and more complex frame dependencies. Keep in mind, however, complexity has a cost, and not every file format has to, or should, support everything. The MPEG-1 file format is improved in a number of ways but is significantly more complex to support with its precise per-byte timing and bandwidth constraints and lack of a central index. In general, the more features that are put into a file format, the nicer it becomes to write and the harder it is to read... and the harder a file format is to read, the less universally it tends to be supported properly. If a file format is way too complex but still becomes popular, generally the number of incomplete and broken clients using it grows and the usable part of the file spec contracts to the part that people actually need. So file format designers beware!

Now, as for AVI files, there are a lot of mistakes that can be made in creating or transferring AVI files, and VirtualDub tries to be tolerant. Here are some of the problems I've seen:

In case it's not clear yet, VirtualDub shouldn't be used to determine that an AVI file is valid, because in the interests of compatibility and recovery it allows a number of violations. It also doesn't support a few of the lesser-used parts of the file format, most notably streams with a non-zero start time and in-stream palette changes. However, I've tried to make the parser accept most damaged AVI files and flag warnings for files that it should but can't support, to improve the usefulness of the program.

By the way... what are OpenDML AVI files?

Earlier, I said that chunks are tagged with a four-byte length. This limits the size of any chunk to ~4GB (4,294,967,295 bytes), and in fact, the practical limit is a lot lower due to compatibility concerns, around 1-2GB. The index also has the same limitation and this limits the size of standard AVI files to 2GB. A group called the OpenDML AVI M-JPEG File Format Subcommittee devised a semi-backwards-compatible way to extend this limit, by appending additional structure to a standard AVI file. The result is that legacy applications still can't read beyond 2GB, but the rest of the data is appended after the standard AVI and pointed to by a new type of two-level index. VirtualDub calls this the AVI2 format; by default it writes standard AVI files until it hits 2GB, at which point it switches to the new format.

Finally, there is one major feature of common AVI files that I haven't mentioned yet: VBR audio. In particular, I mean VBR MP3 audio. For various reasons VBR audio both is and isn't supported in the file format, and the way that it is implemented in practice is also both supported and not supported. In a future post I'll go into the technical details of how VBR MP3 audio is popularly implemented and the reasons for VirtualDub's behavior with it. I already wrote on this a long time ago, but it's a common enough question that the answer bears repeating.


Comments posted:

Ah... things are clicking into place in my brain now :-)
Many thanks for the intelligence within VirtualDub. Its saved (for the most part) many avi's from scratched CDs.

Very informative reading these posts about VirtualDub and a/v media. Thanks for sharing with us.

SonOfAdam - 11 11 04 - 07:09

You may find AVIMaster ( useful, which focuses on parsing and reconstructing the structure of AVIs (and I'm quite proud what it ingests) and issuing warnings on conformance. So you get a report on the file, statistics and all, and if necessary an as good as possible remake. Warning: command line utility...

Thomas Ziegler (link) - 11 11 04 - 13:23

Don't forget applications that write bad dwDuration values into the indx chunk :D :D

Concerning "VBR MP3", it seems to work really nicely, as the same thing works with AAC and HE-AAC as well, even with M$'s b0rked AVI splitter. "Frame-wise" is not necessary; AVI-Mux GUI successfully puts several MP3 VBR frames into one chunk now if the user wants to.

Also, "Open DML 1.02" actually requires that the first RIFF list be not larger than 1 GB. I don't know which idiot set the limit to 1 GB, but it is there

Alexander Noé - 11 11 04 - 14:11

I did fix that dwDuration bug as soon as I heard about it. :)

Sadly, in practice the compatibility features of OpenDML hierarchical indexing are not very useful because older programs balk when they can't read the whole file (dwLength in the stream header points beyond valid data in the legacy index).

VBR audio does not work really nicely -- it breaks compatibility with several parsers. More on that next time.

Phaeron - 12 11 04 - 00:07

Again, I just have to say I love reading these posts. I really enjoy the details and information contained in them. I am learning, rather quickly, about things that would take me months, perhaps, to learn elsewhere.

Abu Hurayrah (link) - 12 11 04 - 22:16

Good Document. Helped to know the basics of AVI format

Xavier - 06 02 05 - 22:45

On another page you wrote "I'm not going to speak on the properness of VBR audio in AVI because almost everyone knows how I feel about this." - Unfortunately despite spending a long time of googling for qualified answer about whether or not VBR audio in .avi files is "acceptable" or not, i still haven't really found any good answers, except for some _very_ technical (and more or less unconcluded) discussions on the topic. Additionally it seems that DivX Networks are encouraging - or at least not warning against - using VBR audio in AVI. They even require hardware vendors to support VBR audio in AVI to become "divx certified"! But is this reasonable?

So i'd be very happy if you could write some of your personal views on this subject. I'm quite concerned about the portability issues, and if this is as bad an idea as i suspect, someone should stop all those people currently using this format!

JoaCHIP (link) - 21 03 05 - 07:01

I am recieving an error message that i have never seen before and i cant seem to find out the answer into resolution. if you could please assist with with this issue - if there is a way around it i would greatly appreciate it.
error -- couldnt locate decompressor for format 'wmv3' (unknown)
virtualdub requires a video for windows (vfw) compatible codec to compress video. directshow codecs, such as those used by windows media player are not suitable.

Kristina Mount - 28 07 05 - 01:34

Kristina Mount: I don't know if you fixed this problem by now, however, I think your solution would be to install the WMV3 (or Windows Media Video v. 3, some time Microsoft calls it v. 9) codec. Go to Microsoft's web-site and download the latest Windows Media Player and install it even if you don't want to use their application. It should install the required codec. I hope this helps you.

Note that I do NOT use/used Windows for the last five years!

Ziyad A. M. AL-Batly - 13 09 05 - 23:34

i want to know how to extract RGB from the avi file in the data chunk.

praveen - 06 12 05 - 01:22

Hey everybody. I have got a problem. I've deleted avi file (compressed from DV video to DivX by DrDivX). Then i noticed, it was deleted. I recovered it, but it can't be played. The proview doesn't show in windows explorer. When i drop it into Virtual Dub is starts to reconstruct missing index block, but after 10 minutes of working i can see only first frame. When svaing Direct stream copy, size doesn't change, but player plays only first frame. It is rather important video for me, and it'll be bad if i loose it. Does anyone knows probable resolution for it? Thanks a lot.

Max - 08 01 06 - 06:28

praveen - for a visual look at how RGB data appears in an uncompressed (full frames) AVI file, open the file in a hex editor (look up "frhed" in google - great free editor), and search for chunks beginning with either "00db" or "01db"; the RGB data for each frame is preceeded by this + a 4 byte value that indicates the size of the frame.
If the video frames in the file are compressed, then you will need to use the appropriate codec to decompress them.
Hope this helps.

Jon - 19 02 06 - 16:52

Earlier someone wrote about problems reading wmv3 files. As another poster noted, this is the Windows Media 9 codec. Go to the Microsoft site and look for the Video for Windows codec for Windows Media 9. Whenever I install a machine I have to poke around a bit to find it and usually its not until the 2nd or 3rd download that I actually get the right one.

Gerald - 13 07 06 - 18:28

I've got a problem:
When saving to avi-file the following error occurs:
'audio samples 477xxxx-477xxxx could not be read from source. The file may be corrupted'
I have to delete a part of the video and that's not what I want.
Is there a way to save the file without deleting this part of the video (with audio!)?

Dusty - 06 08 06 - 14:04

I have an important AVI file taken on a Fuji Finepix F30 that was inadvertently corrupted by plugging in the power cord during a transfer. No data recovery software has been able to extract a working AVI file. The video is actually encoded using M-JPEG and the audio is mono wave. I was trying to find out if there are any utilities that would work better than what I've tried:

Easy Recovery Ver 6.1
R-Studio Ver 3.0
BinaryBiz VirtualLab Data recovery v5.5.
File Scavenger 3.exe
GetDataBack for FAT V3.03
PC Inspector Smart Recovery 4.43.exe
Restorer2000 Pro 3 build 123007.exe
Stellar Phoenix Windows (FAT & NTFS).exe
Zero Assumption Recovery 8.0.exe
f_recovery_xdver 2.5

In a few instances an AVI file was recovered that was unplayable. Also, in one instance FIL0.AVI was found immediately followed by FIL0.MOF and FIL1.MOF. I think the MOF files may correspond to the video MJPEG stream, though Im not sure.

I also tried these recovery programs that were specifically designed for recovering pictures/camera data:

Magic Photo Recovery PRO v3.0.exe
FileRecovery for xD-Picture Card
PhotoRescue 2.1 Demo wizard.exe
PhotoRescue 2.1 Expert Demo Version 682

None was especially helpful.

For the unworkable AVI files I was able to recover, I tried the following programs in hopes of correcting the internal inconsistencies:

ASF-AVI-RM-WMV Repair v1.82.exe
AVImedic 5.3a
Divx Avi Asf Wmv Wma Rm Rmvb Fix Joiner
DivX Repair 1.3.exe
Video fixer 3.23.exe

None worked!

What the file signature is and detailed info relevant to the MJPEG stream that might allow me to recover the data manually? Im not afraid of getting dirty with a hex editor if need be.



John Whitlow - 09 11 06 - 10:28

I looked into divx avi created in direct show and see 00db and 00dc data chhunks. Similar file created by other program has only 00db. What is the difference between 00db and 00dc data chunks.

anatolik - 20 11 06 - 02:40

What is the best way to capture a video stream from a vcr tape, and encode it to avi and clean it up a bit, bu tkeep the file size near vcd levels, WHEN armed with virtual dub? I have been capturing files with virtual dub, but get alot of sync problems but this is my processor running at or near 100% it seems, so now i have been capturing uncompressed and no more sync problems. so now what, i have read alot of articles... i am guessing to use virtual dub to a lamemp3/divxmp4 format. i notice that when i capture into divx at 2500kbps on the divx codec filter, the video states to be capturing at near 700kbps on VD. this is confusing. So i hear we can nicely fit atleast 2hrs video onto a cd-r, so i assume that near 800kbps max on the video encoding and using mp3 audio is all that is needed to nicely achieve this.

If thats all, then what about any filtering though? Inverse Telecine? and any extra interleaving, smoothing a good idea? I sometimes like a 15% sharp as the only needed filter, when capturing into divx. But my processor cant handle this, so i have to introduce another step that adds hours to the process... Of course that extra step was to capture raw, then filter after on a second pass. I thought virtual dub would be good for a one run, capture into a filtered finalized avi. DO i just need a good processor? Or is the payoff just WAY better to capture raw, then encode after?

Brian (link) - 06 02 07 - 03:00

by the way, im using a pinnacle capture card, and have composite in from the vcr

Brian - 06 02 07 - 03:04

ok, im back at it, i have been recapturing with a super processor now(1,5Ghzfsb,pc6400DDR2-2GB-am2), and no more processor clipping problems. i find that i have been able to squeeze video and audio compression and still maintain a grip on sync, but still no cigar. its not quite good enough. Maybe theres a good format out there for capturing? i try even raw capture, with no audio or video compression, and still end up with sync problems. whats the deal? is it just the way vcr tapes screw up the sync rates? i believe capturing from the tv signal has NO sync problems, then when i push play ont he tape, i watch my sync meters go off the screen for a bit until they funally go into a wavy oscillation. the resample rate gets all the way around +4 to +4, and at something like .97 times, and the resync goes near 100ms, i know this is not too bad, and my processor seems to be hanging on to the sync, but the end result is still out of sync. again, when i capture from the regular tv tuner through the vcr, the lines are all merged and synced. still learning...
p.s. thanks for the awesome virtual dub support, i couldnt be digitizing my entire vhs library without you!! hats off!

brian (link) - 02 05 07 - 13:53

I've been having problems with my avi's I try to import them into my Windows movie maker and adobe premier and they can't find some sort of codec. It worked perfectly before I have no idea what's happening!! could someone help me?

Rose - 02 06 07 - 00:03

I have been unsuccessful in recombining four AVI files. I am able to open up the first file, but then I receive a series of error messages:
[!] AVI: Index not found or damaged -- reconstructing via file scan.
[!] AVI: Invalid chunk detected at 272618258. Enabling aggressive recovery mode.
[!] AVI: Keyframe flag reconstruction was not specified in open options and the video stream is not a known keyframe-only type. Seeking in the video stream may be extremely slow.

What do I do?
[!] AVI: Variable bitrate (VBR) audio detected. VBR audio in AVI is
non-standard and you may encounter sync errors up to 7154ms when
attempting to extract WAV files or processing the audio in Direct Stream
Copy mode. Full Processing mode is recommended to decompress or recompress
the audio. (bitrate: 127.9 18.3 kbps)

George - 19 06 07 - 16:49

Very interesting to learn about AVIs and how they work. I am having troubles exactly like Max's where i accidentally deleted some AVI's and recovered them. Some of the AVI's work, the preview shows up and they open just great. Others, not so much. It says they are an AVI but they have no thumbnail preview and when I try to open them Windows says something like a codec not found. These AVI's worked fine before. I have tried several AVI recovery softwares with no avail. Some say they "fixed" the files but they still wont open. One said it was due to bad frames at random points throughout the file and it fixed the files by skipping those frames, it still did not work after.Is there something i'm missing here? Help, i really want to get these AVI's back!

Jeremy - 03 07 07 - 11:06

I wanted to know how seeking can be made possible in AVI files. This is required for the support of fast forward & rewind. As far as my knowledge is there i dont think there is any timestamp information is available in the AVI file. If it is , then please someone let me know where or how can i calculate.

G Bansidhar - 23 07 07 - 11:30

I'm using virtualdub 1.9.9 to capture AVI files. I then use software I have written to do processing on said files. My program opens the AVI file and looks at the main 'avih' header at the start of the file to extract the number of frames. It seems that virtualdub is writting incorrect values to the dwTotalFrames, I have to seek into the 'strh' vids chuck and extract the correct value from dwLength. I tried recording with fraps and hypercam which produce correct files so I have narrowd down the problem to virtualdub. Its not a major problem but still, it is incorrect. Sorry if this is the wrong place to post, I hope somebody reads this.

Mark - 12 09 10 - 06:43

Ignore my above post, it seems its correct behaviour for AVI 2.0 RIFF file format, if the avi contains AVIX chunks.

Mark - 13 09 10 - 00:50

I use Virtual dub 1.9.11 to dub a movie. But as soon as i open a media file, it shows an error. The error is as follows :

Couldn't locate decompresser for format 'XVID' (unknown)
Virtual Dub requires a Video for windows (VFW) compatible codec to decompress video. Direct Show codecs, such as those used by Windows Media Player, are not suitable.

Kindly help me with this problem and post here only. Please help fast.

Yogesh Prasher - 11 04 11 - 16:51

I have donload a 997mb *.avi file and it plays the first 18secs then opens up some spam website !! I have tried cutting the avi but the programs only identify that there are 18secs of play tim eout of the 997mb ?? and help on this matter or is it a dump file

Adam - 01 05 11 - 01:25

Yogesh are you converting MOV to AVI? try to convert using MJPEG. (FormatFactory)

Bob - 24 06 11 - 15:02

is there a list of codecs that virtualdub is compatible with? i would really like to use the program but it doesnt open half the video files i try to feed it. could such a list appear in a "compatibility" section somewhere in the documentation or the website? thanks.

i also get the VFW error by the way. google brought me here.

josh - 26 01 12 - 04:06

my video keeps freezing after i've apprehend some videos together and save in there any way to make sure it doesnt freeze when i play it in avi? (using virtualdub 1.9.11)

PROBLEM - 15 02 12 - 00:55

I have a problem on .srt file it says that the first sub start on and after I saved the video with the subs the same sub starts earlier what is the problem???

George - 04 06 12 - 01:20

I produce videos for our church. I receive AVI files that virtual dub reports "Invalid AVI file: The main 'movi' block is missing." When I use the hex editor, I see the movi block starting at 0x10000 with 'movi' characters just before the data at 0x10000. I have to use Super to convert from AVI to AVI in order to be able edit them with virtual dub. I would like to eliminate the conversion step as it doubles the raw disk space I need to process and takes hours. These are big files up to 90 minutes in length. Can you suggest anything I could try to debug the problem. I am wondering if it is a codec problem The files work fine in Windows Media Player, but not in VLC.

Rich - 18 08 12 - 04:58

It looks like the idx1 section is missing on the file. Is there a way to regenerate it other than using conversion software (like Super) to do it?

Rich - 19 08 12 - 01:02

Even though this may sound extremely arrogant I must say, up front, that I have not read through your post.

In actual fact, I have not read through it *on purpose* because this simple question has *never*, to my knowledge, received an equally simple response. It's as if someone asked "how can I open a '.dat' file in notepad?" and the answer begins by explaining how various storage media work, then file systems, then on to a near dissertation about file formats and on and on forever.

And still, every time, at the end of the post, long forgotten and unanswered is the famous question.

I know that a GENERAL answer does not exist. I think most people are aware of that.

However, and I think most people would agree with this as well, if someone asked "how can I open up an .avi file in VirtualDub that was encoded with XviD?" they would receive an immediate response as follows:

"Oh, XviD? That's easy! Just go to here [insert URL] and click on the "download" then "install" button, and then it will work.

So here's my question:

Are there any AVI file formats that are as easily integrated into Virtual Dub as XviD? If so, what are they? What "codec"s are they related to? if any? And where does one download the non-VFW-encoder/decoders for these formats so that one might at least open *those types of files* in Virtual Dub?

Because as you can easily see, only 2 posts before mine someone has said "The files work fine in Windows Media Player ..." which is completely unrelated to whether or not they can be opened in Virtual Dub! The error message even says so! (ie. THE FAMOUS VFW ERROR MESSAGE: "blah blah blah Direct Show codecs, such as those used by Windows Media Player, are not suitable.")

That much I understand. Those codecs are not suitable. Check ✔

A) Okay then, what *is* suitable?


B) *where* are they to be found?

- Alan

Alan Carre - 12 08 14 - 13:35

Ok, I just downloaded and tried using Virtualdub for the first time on Windows 10. I have a Canopus ADVC as my capture device going through a firewire connection. I am able to see the video, but most all the options that should come up in Virtualdub are no where to be found. It's as if something isn't being recognized and I have no ability for options on any of the tabs, nothing at bottom of screen, no details, etc. What could be causing this? Are there codecs missing that would allow all the options to show up? The audio comes through but you can hear a constant background 'beat' very low even when there should be silence. What is this? Thanks!

Lee - 28 02 16 - 09:03

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