[vlc-devel] Some codec/demux/display bugs

Cyril Lambin cyril at nolife-tv.com
Mon Oct 10 17:35:53 CEST 2011

Hello everyone,

Here are a few issues we constantly run into at Nolife where we use VLC as a
monitoring/video checking solution. I included some example files.

All those issues are present in VLC 1.1.11 for Windows. When checking our
videos, VLC is always set to auto deinterlace with Yadif 2x selected.

1) Codec issue : Blackmagic MJPEG

VLC doesn't decode properly MJPEG videos created using a Decklink Blackmagic
Studio 2 card. Video fields (odd/even) are always spatially switched. In
addition the field dominance is not correctly interpreted in PAL (NTSC=lower
field first, PAL=upper field first).

2) Demux issue : DV Quicktime generated by Final Cut Pro 7

This is an old bug that jb tracked when he came to see us months ago.
Quicktime DV files exported by Final Cut Pro doesn't read properly - it was
a demux issue, and I think it was previously fixed.
It's also been reported on the current OSX version of VLC.


3) Display issue : on-the-fly aspect ratio switch

When reading Quicktime DV files, VLC tries to guess the aspect ratio of the
file. I don't really know how it does that, I know it does it properly with
MPEG2 TS files (where aspect ratio can be different for each frame) but for
some Quicktime files it just doesn't work.
For instance for 16/9 anamorphic DV files, instead of looking for the
QuickTime header, it seems to look for aspect ratio information in the raw
DV stream. In the following video you can see it doesn't really work since
video editing software like Avid Media Composer discard the ratio
information for every frame it needs to work on (adding titles etc), so
eventually the only aspect ratio information to be used is the one that VLC
may find in the Quicktime headers.

The other problem is that forcing the video aspect ratio to 16/9 in VLC
doesn't work, it's just ignored.


Thanks a lot.

Cyril Lambin

Cyril Lambin - Nolife
Directeur Technique
3 villa du clos de Malevart
75011 Paris
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