VirtualDubMod FAQ


VirtualDubMod FAQ

What do I need to run VirtualDubMod?
Read this if VirtualDubMod doesn't run for some reason!
Get the latest release and unpack it somewhere on your HD.
Get the latest Dll pack and unpack it in the same directory.
If you don't have all the VirtualDub Dlls (sylia.dll, vdrslink.dll, etc.) get them (either coming from the official VirtualDub, or go get the latest special Dll pack with those files from SourceForge).

If you want AviSynth syntax coloring you also need AviSynthLexer.lexer. Syntax coloring for commands from external plug-ins works since AviSynth 2.5.2.

There will be also some translation packs available.

I found a bug / I want to propose this feature. What should I do?

  1. All bug reports and feature requests go to the Trackers on our project page on SourceForge. You don't need to register there to be able to report, but doing so has a big advantage. Whenever somebody comments on your request, you will get a notification email, so you will asap know when something is up.
  2. Make sure your request hasn't been reported before! We (the developers) close the items that are resolved, so make sure you select "All" in the status box on the respective tracker (normally only the open items are shown). Please take also the time to look at the current Changlog. You can find this via the SF CVS browser (CVS->Browse CVS Repository->VirtualDubMod15->VirtualDub->mod->res->Changes Mod.txt (click on the version number right of the file name))
  3. The status of all bugs regarding 1.4.x has been changed to 'Pending' after the release of 1.5.x. This was done to get rid of stuff that doenst apply anymore due to the major changes. If you find your bug to still exist, please change its status back to open instead of submitting it anew.
Of course you can also post your stuff in the forum for discussion, but always add it to the respective tracker, otherwise bookkeeping is hell for us and items might slip out. We all are only humans, so we might overlook important stuff if it's not collected at a central point.

Where has the audio menu gone to?
Right mouse button in the stream list.

How do I use 'Open via AviSynth'?
This allows you to open any AVISynth compatible video file by automatically generating a suitable script by a selectable template. These templates go into the 'templates' directory in your VirtualDub directory. Template syntax is the same as for AVISynthesizer (I included readme_AVISynthesizer.txt because as of this writing the AVISynthesizer homepage is not available). You can choose the default template shown in the open dialog by starting the template description with "Default" (note that the template filename has nothing to do with this).
This function has no intelligence whatsoever! You're responsible to choose the right template for the file (eg a SegmentedAVISource template for multi-segment avis or giving the right fps to DirectShowSource)
For this to work flawlessly you need AVISynth 2.05 and a correctly set plugin directory. (Create a registry key called "PluginDir" in HKEY_LOCAL_MACHINE\Software\Avisynth\)
A workaround if you don't want to do this is adding the needed LoadPlugin lines into the templates.

Why is using vbr mp3 in avis a bad idea?
We discussed this issue at length in irc and Cyrius (suiryc) gave a pretty good explanation:

[21:33] <Belgabor|Home> cyrius, what did your experimets tell?
[21:33] <Suiryc> Belgabor|Home : I think I know know why VBR is not good, and also why Nando's hack works (somehow)
[21:33] <Suiryc> s/know/now
[21:33] <Belgabor|Home> ok, tell me
[21:33] <Suiryc> :)
[21:34] <Suiryc> first of all there are 2 'headers' in the AVI (audio) stream
[21:34] <Belgabor|Home> I have the feeling i need to hammer that down some throat soon :p
[21:34] <ChristianHJW> lol
[21:34] <Suiryc> first one is a general one (the same struture is used for each track)
[21:35] <Suiryc> AVISTREAMINFO
[21:35] <Suiryc> (IIRC ... there should use shorter names ...)
[21:35] <Belgabor|Home> lol
[21:37] <spyder482> ChristianHJW: I won't be moving for a few months still though
[21:37] <Suiryc> this one tell how many frames there are in the stream
[21:37] <Suiryc> and what is the rate of the frames
[21:37] <Suiryc> thanks to dwRate & dwScale fields
[21:37] <Belgabor|Home> got that
[21:38] <Suiryc> it also contains a field saying the size of 1 frame
[21:38] <Suiryc> if VBR, then it is set to 0, otherwise it is set to the correct value
[21:38] <Belgabor|Home> dwSampleSize
[21:39] <Suiryc> yep
[21:39] <Suiryc> then there is a header specific to the audio stream (based on WAVEFORMATEX)
[21:39] <Suiryc> this one tell the samplerate (44100, 48000, ...)
[21:39] <Suiryc> the byterate
[21:39] <Suiryc> the format (wFormatTag)
[21:40] <Suiryc> and especially contains a field names nBlockAlign
[21:40] <Suiryc> nBlockAlign tell how many bytes an audio frame contains
[21:40] <Suiryc> _BUT_
[21:40] <Belgabor|Home> And that musnt be 0
[21:40] <Suiryc> cannot be set to 0
[21:40] <spyder482> so much work for AVI...
[21:40] <Suiryc> :)
[21:40] <Belgabor|Home> ok, i think i get the picture
[21:40] <Suiryc> ok so let's continue
[21:41] <Belgabor|Home> ok
[21:41] <ChristianHJW> all with you guys ...
[21:41] <Suiryc> in Nandub here is what happens with an MP3 stream (VBR one)
[21:42] <Suiryc> Nando set dwRate to the samplerate (44100, 48000, ...)
[21:42] <spyder482> don't you two have a channel for this? :)
[21:42] <Suiryc> spyder482 : shut up :P
[21:42] <Suiryc> and set dwScale to 1152
[21:42] <spyder482> lol
[21:42] <Belgabor|Home> no, the other one is just for lurking
[21:42] <Belgabor|Home> :p
[21:42] <Suiryc> :]
[21:42] <spyder482> hehe
[21:43] <Suiryc> and set nBlockAlign to 1152 too
[21:43] <Suiryc> then, when muxing it only treat whole MP3 frames
[21:43] <Suiryc> (i.e. each MP3 frame is in its own Chunk)
[21:44] <Suiryc> you still follow ?
[21:44] <md`> who has done the mpeg2 import part of vdmod?
[21:44] <Belgabor|Home> ok, one mp3 frame is what?
[21:44] <Belgabor|Home> pulco-citron
[21:44] <md`> hmpf
[21:44] <spyder482> pulco-citron
[21:44] <spyder482> oh
[21:44] <spyder482> :)
[21:45] <md`> why does he generate d2v and dont let the user decide to pick one...
[21:45] <Belgabor|Home> dunno
[21:45] <md`> if there is one already
[21:45] <md`> hmmm
[21:45] <Suiryc> Belgabor|Home : an Mpeg1-Layer3 frame is the shorter block of data you can use
[21:45] <ChristianHJW> let Suiryc finish guys .. please
[21:45] <md`> yes ok
[21:45] <Belgabor|Home> ok
[21:45] <spyder482> ChristianHJW: check #virtualdub
[21:45] <Suiryc> it contains an header saying what is in the frame, and then the data (audio)
[21:46] <ChristianHJW> we have to know whats wrong in AVI to be able to advertise matroska ;-)
[21:46] <Belgabor|Home> this is how much data?
[21:46] <Suiryc> somehow 1 MP3 frame ~ 1 video frame
[21:46] <Belgabor|Home> ChristianHJW: lol
[21:46] <Suiryc> the size of a frame depends on the MP3 settings
[21:46] <Suiryc> (i.e. bitrate, ...)
[21:46] <Belgabor|Home> ok
[21:47] <Belgabor|Home> is it fixed for a file or varible in vbr?
[21:47] <Suiryc> however a Mpeg1-layer3 frame conatins 1152 samples
[21:47] <Suiryc> the size of a frame is variable
[21:47] <Suiryc> even in CBR
[21:48] <Suiryc> (e.g. frames will be of 417 or 418 bytes)
[21:48] <Belgabor|Home> ok, but 1152 is the upper limit?
[21:48] <Suiryc> because a fixed btrate must be achieved
[21:48] <Suiryc> 1152 is the number of samples a frame contains
[21:48] <Suiryc> each frame (whatever its size may be) contains 1152 samples
[21:49] <Belgabor|Home> oic
[21:49] <Suiryc> so let's continue ;)
[21:49] <Suiryc> each frame contains 1152 samples
[21:49] <Belgabor|Home> ok
[21:49] <Suiryc> and the rate of the stream (in AVISTREAMINFO) has been set to :
[21:49] <Suiryc> dwRate / dwScale = SampleRate/1152
[21:50] <Suiryc> since each Frame contains 1152 it is equal to the 'framerate'
[21:50] <Suiryc> (as for video)
[21:50] <Belgabor|Home> ok, i think i got that
[21:50] <Suiryc> now you must recall that each frame is in its own AVI chunk
[21:50] <Belgabor|Home> ok
[21:50] <Suiryc> so it is also the 'chunkrate'
[21:51] <Suiryc> so here is now what happens (it is most likely what happens) when playing the file in Window Media Player
[21:51] <Belgabor|Home> ic
[21:51] <Suiryc> WMP will get both headers
[21:52] <Suiryc> which will say to it that the rate of the stream is SampleRate/1152
[21:52] <Belgabor|Home> gimme a sec, brb
[21:52] <Suiryc> and that each audio frame is 1152 bytes long (nBlockAlign)
[21:52] <Suiryc> k
[21:53] <Belgabor|Home> back
[21:54] <Suiryc> ok so WMP believe each frame is 1152 bytes long
[21:54] <Belgabor|Home> yeah
[21:54] <Suiryc> which is not the case (generally frames are around 400 bytes long with 128kbps stream)
[21:55] <Suiryc> but
[21:55] <Belgabor|Home> yeah, got that much
[21:55] <Suiryc> now you are reading data in the file
[21:55] <Suiryc> and WMP needs to know when to read the audio
[21:55] <Suiryc> (i.e. to which time correspond an audio frame)
[21:56] <Suiryc> to do so it will look at all the previous audio chunks in the file
[21:56] <Suiryc> for each shunk it divide the size (in bytes) of the chunk by nBlockAlign to know how many frames there were in the chunk
[21:56] <Belgabor|Home> ok
[21:56] <Suiryc> s/shunk/chunk
[21:57] <Belgabor|Home> ok
[21:57] <Suiryc> (since every tools dealing with the stream must cut on nBlockAlign boundaries)
[21:57] <Suiryc> since each chunk is shorter than 1152 bytes (nBlockAling) it shoul get 0
[21:57] <Suiryc> but this is not possible
[21:58] <Suiryc> since tools work on blocks of nBlockAlign bytes, it must assume than there is at least 1 frame in the chunk
[21:58] <Suiryc> (even if the chunk is shorter)
[21:59] <Suiryc> so for each chunk it find there is 1 frame in it
[21:59] <Suiryc> which is really the case (each mp3 frame is in its own chunk)
[21:59] <Suiryc> so WMP got the correct number of mp3 frames played so far
[22:00] <Suiryc> and since it has the correct rate (each frame contains 1152 samples, and the rate of the stream is SampleRate/1152)
[22:00] <Suiryc> it also got the correct timecode for the frame
[22:00] <Belgabor|Home> ok
[22:00] <Suiryc> resulting in a perfectly synched MP3 stream
[22:01] <Suiryc> I was lead to this conclusion without debugging WMP while playing ;) but with some tests I made :
[22:02] <Suiryc> I changed the dwScale value (with or without the nBlockAlign value)
[22:02] <Suiryc> but this resulted in otu of synch issues (audio playing too fast/slow)
[22:02] <Suiryc> out*
[22:02] <Suiryc> I changed the nBlockAlign valuie :
[22:03] <Suiryc> setting it to 1 and then I have out of synch issues too
[22:03] <Suiryc> but setting it 2304 and I stil have a perfectly synched stream
[22:03] <Belgabor|Home> ok
[22:04] <Suiryc> so in fact the 1152 value in nBlockAlign could be anything else
[22:04] <Suiryc> _but_
[22:04] <Suiryc> must be higher than the size of an mp3 frame
[22:04] <Belgabor|Home> ok, what happens if you set it to 0?
[22:04] <Suiryc> lol
[22:05] <Suiryc> if you set it to 0 then WMP won't play the stream (the icon for audio is disabled like if there is no audio in the file)
[22:05] <Suiryc> so no VBR ;)
[22:05] <Belgabor|Home> ok
[22:06] <Belgabor|Home> so the failure is in priciple not in avi, but in the WAVEFORMATEX header
[22:06] <Suiryc> yep
[22:06] <Suiryc> but since the AVI will use WAVEFORMATEX for audio headers, it is still a failure in AVI specs
[22:07] <Belgabor|Home> do you have the resemblance of an idea why vbr mp3 fails?
[22:07] <Belgabor|Home> yep
[22:07] <Suiryc> <Belgabor|Home> do you have the resemblance of an idea why vbr mp3 fails? <-- you mean why it is not good ?
[22:08] <Belgabor|Home> yep, why it fails sometimes
[22:08] <ChristianHJW> thats what i am interested in also
[22:08] <Suiryc> well in the case of WMP, it will divide the chunk size by nBlockAlign
[22:08] <Suiryc> (that's what I think, since the synch is good)
[22:08] <Suiryc> and will set it to 1 if the chunk size is too small
[22:09] <Suiryc> but there is another way to compute timecode
[22:09] <Suiryc> (assuming that you have CBR of course)
[22:09] <Suiryc> you take the total bytes in previous chunks
[22:09] <Suiryc> and divide it by nblockAlign
[22:10] <Belgabor|Home> which fails miserably for the vbr hack
[22:10] <Suiryc> of course in this case you get a completly wrong value since mp3 frames are not 1152 bytes lnog
[22:10] <Suiryc> yep
[22:10] <Suiryc> otehr tools may also assume that the chunk is not valid (corrputed) since its size is shorter than nBlockAlign
[22:11] <Belgabor|Home> ok, thats the failure in principle, but why are some files broken?
[22:12] <Suiryc> what files ?
[22:12] <Suiryc> broken ? what do you mean by broken ?
[22:13] <Belgabor|Home> i had some vbr mp3 avis which seemed like having divx3 freeze frames but where ok when demuxed
[22:13] <Suiryc> dunno
[22:13] <Suiryc> maybe a problem with the decoder
[22:14] <Belgabor|Home> ok, well that cleared things up a bit
[22:14] <Belgabor|Home> thx :)
[22:14] <Suiryc> :)
[22:14] <Suiryc> btw there may be problems with Nandub code ;)
[22:14] <Suiryc> because :
[22:14] <Suiryc> 1. layer1 streams only have 384 samples per frame
[22:15] <Suiryc> 2. IIRC with very high bitrates an mp3 frame can be higher than 1152 bytes ;)
[22:15] <Suiryc> s/higher/bigger
[22:16] <Suiryc> (the max size is near 2000 bytes IIRC)
[22:16] <Belgabor|Home> ok, so nBlockAlign should be >2000
[22:17] <Suiryc> so depending on the way dividing is used (rounding to floor or ceil or nearest value)
[22:17] <Suiryc> and the max size of a frame, it may find there are 2 frames in a chunk where there is only 1 frame
[22:17] <Belgabor|Home> ok, i got that
[22:18] <Suiryc> but this is for really high bitrates ...
[22:18] <Suiryc> lemme check ...
[22:19] <Belgabor|Home> what would happen if we put two frames in one chunk? aka set dwRate = 2* sample rate and so on?
[22:20] <Belgabor|Home> no, not two, just double the values?
[22:21] <Suiryc> if you double the value the rate of the audio will be changed accordingly
[22:21] <Suiryc> so to keep it correct you would have to put 2 mp3 frames in each chunk
[22:22] <Suiryc> but then you would most likely go beyond the 1152 bytes per chunk
[22:22] <Suiryc> and increase the chances to generate out of synch problems
[22:23] <Belgabor|Home> let me rethink
[22:24] <Suiryc> changing dwRate and dwScale only affects the rate of the stream
[22:25] <Suiryc> multiplying dwRate by 2 => audio play 2 times faster
[22:25] <Suiryc> multiplying dwScale by 2 => audio play 2 times slower
[22:25] <Belgabor|Home> if we double dwrate, dwscale, nblockalign and dwsamplesize?
[22:25] <Suiryc> multipyling both => no change
[22:25] <Suiryc> dwSampleSize is set to 0
[22:26] <Belgabor|Home> ah ok, so skip that
[22:26] <Suiryc> (dwRate, dwScale) and nBlockAlign are not linked
[22:26] <Suiryc> you can use a higher value in nBlockAlign
[22:27] <Suiryc> (like the 2304 I tested)
[22:27] <Belgabor|Home> nvertheless, if we double all three, shouldnt it be safe for larger mp3 frames?
[22:27] <Suiryc> this won't change anything in the case of WMP because something lower than 1152 divided by 1152 or 2304 will still be rounded to 0
[22:27] <Suiryc> Belgabor|Home : this would be safer
[22:28] <Suiryc> but would cause even more troubles in apps that don't work the same way than Nandub & WMP
[22:28] <Suiryc> I think some apps sometimes check a value of 1152 to know it was made by Nandub
[22:28] <Belgabor|Home> ok, i see the point
[22:29] <Belgabor|Home> faulty concept stays faulty
[22:33] <Suiryc> k I checked
[22:33] <Suiryc> keeping 1152 shoudln't cause too much problems
[22:33] <Suiryc> for Mpeg1-Layer2/3 the mas is near 1750 bytes long
[22:34] <Suiryc> there could be problems with Mpeg2/2.5-layer2/3
[22:34] <Suiryc> where a 160kbps stream of 8kHz have frames of 2881 bytes long at most
[22:35] <Suiryc> anyway I don't think people use this kind of stream ;)
[22:36] <ChristianHJW> highly unlikely ..
[22:51] <Suiryc> nite
[22:52] * Suiryc has left #matroska

The central problem is (imho) it works now. As soon as M$ changes the rounding function in their avi parser from ceil to something else, it will stop working.