[Bf-vfx] Problems and bugs regarding VFX editing in Blender

[Troy Sobotka]

On Mon, Sep 26, 2011 at 2:30 PM,  <maciej.szczesnik at autograf.pl> wrote:
> but there is no way to preview a part of the movie. You have to render each time you want to see what you get. That makes tweaking things a lot more complicated and time consuming. I guest that live preview is not easy to achieve, when 3d rendering is used for placing video elements onto anoth
>  er video element.

Hover over the timeline and press s to set a start frame then e to set
an end frame to render a smaller clip. Further, you can set a
"Preview" range if you are only viewing via the UI.

Realtime viewport manipulations in the compositor are likely in the
near future[1].

> 1. Crash on movie preview in 3d window. If you have a movie assigned as background in a 3d view, Blender often crashes when scrubing through timeline

If you can, try to catch a backtrace on this please and file a bug report.

> 2. There is a problem with transparent quicktime videos. These are quite often used as source video files for various VFX (for example, I've bought Action Essentials 2 from videocopilot.net). It seems that in some cases Blender isn't able to read the alpha channel from quicktime video.

When you speak of "transparent Quicktime videos" you are actually
talking about a wrapper with a codec inside. I'll make an assumption
you mean an h264  via an MOV with an alpha channel. To the best of my
knowledge, the h264 specification doesn't support alpha channels[2],
and as such, most decoders probably will fail on this. Further still,
h264 encoded alpha channel are likely sub optimal as a result of
compression.

With respect,
TJS

[1] http://ocl.atmind.nl/doku.php?id=design:proposal:compositor-redesign

[2] Section 3.5 of the ITU-T Rec. H.264 Specification 06/2011 "3.5
alpha blending: A process not specified by this Recommendation |
International Standard, in which an auxiliary coded picture is used in
combination with a primary coded picture and with other data not
specified by this Recommendation | International Standard in the
display process. In an alpha blending process, the samples of an
auxiliary coded picture are interpreted as indications of the degree
of opacity (or, equivalently, the degrees of transparency) associated
with the corresponding luma samples of the primary coded picture."