[vlc-devel] Re: DV Hangs, Audio continues

Vaclav Koldus vaclav.koldus at avpark.cz
Thu Oct 20 00:23:26 CEST 2005

On Wed, 19 Oct 2005 23:49:46 +0200, Stefan de Konink <skinkie at xs4all.nl>  

> Vaclav Koldus wrote:
>> Stefan, please could you share us your conclusions? I'm curious about
>> it  too.
> Yesterday I mailed with serveral authors of tools including mpeg4ip and
> avidemux, I have more than basic understanding of the DV format so I
> know in what direction I need to search.
> What I know is that the avi container, especially the indexing makes the
> files hang, but thats not the only thing. Premiere seems to store the
> audio in the AVI file. Not in the DV stream as it does when exporting
> back to the camera.
> Basically you have the original AVI(DV(A+V) + A).
>> What comes to my mind is to write a fake decoder module for VLC which
>> dumps your stream into a file before it's decoded. VLC should demux it
>> for  you, even with OpenDML support, and then send it into your decoder,
>> which  dumps it on disk.
> I tryed this with mencoder, material from the Sony-FX1 camcorder
> produced semi-good results, it played the rawvideo (thus audio+video) in
> VLC, but no background music or good audio cuts because that is stored
> inside the A part of the AVI file.
> But I entered another domain of problems. Two girls around 15 you don't
> give a Sony FX1 camcorder to toy around with, so you give them a little
> less expensive DV-camcoder. This little less expesive camcoder seems to
> produce probably LP audio, which is played twice as quick. I didn't find
> out if this was hardware related or software related, we use the same
> camera do to quick transfers to laptop on location.
> After I got some results I ended up to just broadcast the next series of
> programs that were available to me. And strangly they don't have any
> problems at all.
> My own hypothesis of this:
> The material is made, the material is edited and put back in DV mode to
> a recorder from premiere, so it is back on tape synced A/V. Then when
> the material is actually needed it is loaded into premiere and saved to
> harddisk in OpenDML but still DV-A and AVI-A are the same.
> The other most likely method is that someone needed to do a quick fix,
> and stored the fix directly to our external harddisk instead of
> exporting it to DV. And importing it again. DV-A and AVI-A can now be
> different, indexing might fail (it does actually in Mplayer) and VLC
> can't keep up its good work for compensating it.
> Ok, maybe a Pentium4 1.7GHz is not up to the task. Or it is, but no one
> started to make some serious optimalisations -> software issue.
> Stefan

All this sounds as messing up with standarts. DV-AVI should be Type 1  
(which means one stream saved in avi as video but actualy containing dv  
audio as well in one stream with avi) or Type 2( which means you have two  
streams in avi, just like avi wants. One DV video stream without sound and  
one DV audio stream). Case when you have actualy two audio streams in one  
avi ('cause one is in DV stream and one is in audio part of avi) should  
never happen!

If this happens in premiere exporting, I'm losing good meaning about this  
software. Maybe you could check the settings of output format if it's set  
up well.

By the way, I say obvious, but this gives you one advice, always use Type  
1 DV Avis when you want to export files back to DV tape :)

Those troubles with sound seems like the other cam uses 22khz or 44khz  
instead of 48khz samplerate, which should not be a prob when converted  
correctly, but obviously somewhere they aren't. Again, it isn't a good  
idea to use lower samplerate, because of interpolation during conversion  
to higher samplerates.

And another facts for this comes to my mind. I've got problems in VLC with  
playing DV Avis even when they are pure Type 1, without any audio stream  
in avi container, which should make any probs with indexing by my opinion.  
Maybe the prob is when VLC demuxes audio and video from DV stream? But why  
it doesn't hang when not using ffmpeg decoder then?

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