[libav-bugs] [Bug 843] New: Feature request: Add 'alpha' option to 'fade' filter

bugzilla at aruru.libav.org bugzilla at aruru.libav.org
Sat Apr 11 17:47:47 CEST 2015


https://bugzilla.libav.org/show_bug.cgi?id=843

            Bug ID: 843
           Summary: Feature request: Add 'alpha' option to 'fade' filter
           Product: Libav
           Version: 11
          Hardware: X86
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: ---
         Component: libavfilter
          Assignee: bugzilla at libav.org
          Reporter: fhollerweger01 at qub.ac.uk

Use case:
=========
I would like to use avconv to add a title screen (title.png, 1280x720) to a
video (in.mp4, also 1280x720) in the following manner:

- Video starts with title screen visible only (covers entire video w/o
transparency)
- After 3 seconds, title screen fades out to reveal actual video underneath

- NB: Audio stream of in.mp4 should start right away with title screen at
0'00", so this is about overlaying (and crossfading) two streams, not about
concatenating them.


How this would be solved in ffmpeg:
===================================
It appears to me that in ffmpeg, tis problem can be solved by adding 'alpha=1'
to the 'fade' filter:

  ffmpeg -y -i in.mp4 -loop 1 -i title.png -filter_complex "[1:v]
fade=out:75:25:alpha=1 [title]; [0:v] [title] overlay" out.mp4


Why this does not work in avconv:
=================================
avconv does not seem to feature an 'alpha' options for the 'fade' filter. If I
omit the 'alpha', as in the following command, then the title screen fades to
black, without revealing the video underneath:

  avconv -y -i in.mp4 -loop 1 -i title.png -filter_complex "[1:v]
fade=out:75:25 [title]; [0:v] [title] overlay" out.mp4


I do not currently know of any other workaround to solve this problem by means
of avconv.

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