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Bug 644372 - Fading/transparency of overlayed clips causes black video
Fading/transparency of overlayed clips causes black video
Status: RESOLVED INCOMPLETE
Product: pitivi
Classification: Other
Component: Rendering
Git
Other Linux
: Normal blocker
: 0.91
Assigned To: Pitivi maintainers
Pitivi maintainers
Depends on:
Blocks:
 
 
Reported: 2011-03-10 05:41 UTC by kxra
Modified: 2014-11-06 20:36 UTC
See Also:
GNOME target: ---
GNOME version: ---



Description kxra 2011-03-10 05:41:08 UTC
Use cases: Fading clips into each other. This bug basically makes layers useless since overlaying clips can't use transparency (and are therefore just like cutting clips and splicing them together). 

Steps to reproduce: Overlay one clip over another. Use transparency on the top layer either by making it less than 100% opaque, or by having it fade out. 

Symptoms: Towards the end of the overlayed clip, there will be a gap of black video and/or a fade to black (instead of fading into the clip in the lower layer) in rendering and usually playback. Audio is normal throughout. 

Additional details: 

 * It seems the top layer renders much more slowly, and begins fading out later than it should. This can be observed with an image as the overlayed clip, but is most obvious when putting one video over another: in the rendered result, the audio for the top layer was not synced up with video for that layer, and the video for the top layer continued after its audio clip ended. 

 * Tested with webm video clip as bottom layer. Top layers tested were: png, png with transparency (in the image, not just as a clip), jpg, webm, avi. 

 * When the same video clip is added twice, cutting a segment of it to use for the top layer, the effect (black video) only lasts a few frames, but for other images and videos it lasts a second or two.  

 * Above might suggest differences in resolution or something else is exacerbating the problem. 

 * Possibly related: https://bugzilla.gnome.org/show_bug.cgi?id=629808#c4
Comment 1 Jean-François Fortin Tam 2011-03-11 21:13:52 UTC
Can't reproduce :(

Tried a timeline similar to this:

    [-- B -]
[----- A ---{X}--- C --\]
                  [------ D ----]


Where
- B can be anything, even a jpeg image with <100% opacity and a resolution that doesn't match the project settings
- A and C are crossfaded together at {X}
- C fades out into D using opacity curves

...And it renders fine. So we still need to pinpoint what's going on.
Comment 2 Jean-François Fortin Tam 2011-03-13 22:11:59 UTC
"gap of black" mentionned here is a symptom of Bug 612797 with transitions/fades.
Comment 3 kxra 2011-03-14 19:08:43 UTC
Just tested with a more sane container (mkv) instead of WebM for the lower layer, and had the same results as when adding the same video clip over itself, that is: 
"When the same video clip is added twice, cutting a segment of it to use for
the top layer, the effect (black video) only lasts a few frames, but for other
images and videos it lasts a second or two."

Which seems to be what Bug 612797 is about so it seems effort should go towards fixing that bug first and see if that helps with the webm-specific effects (black frame lasting a second or more).
Comment 4 kxra 2011-05-10 00:56:05 UTC
Using Ogg Theora as format for the input file (on the bottom layer, at least!) gets around this and 629808 entirely!
Comment 5 Jean-François Fortin Tam 2013-09-30 19:34:04 UTC
Hi there,

As Pitivi 0.91 has now been released, we would like to encourage you to test it.

It is quite possible that your issue is fixed in this version,
as it is a very significant technical overhaul compared to the 0.15 series.
Read more about the 0.91 release here: http://wiki.pitivi.org/wiki/0.91

If you can reproduce this bug against 0.91 or newer (such as the git version),
please update this bug report accordingly with detailed instructions to
reproduce the bug, updated sample files/projects in xges format, etc.

Drop by our IRC channel if you need help getting started or want to help out!

Thanks!
Comment 6 Jean-François Fortin Tam 2014-11-06 20:36:28 UTC
Closing this bug report as no further information has been provided.
Please feel free to reopen if the issue persists with 0.94 or newer
and if you can provide the information asked for. Thanks!