[FFmpeg-user] Alpha Channel QT with SubTitles

Gandharv Bhagat fradac at hotmail.com
Tue Feb 6 12:01:19 EET 2018

hey Carl,

I generated the test file and no subs are rendered from the subs2.mov file. I see the test pattern/colorbars/clock.  Instead of using a transparent PNG, could I instead generate an alpha channel 1920x1080 canvas directly from ffmpeg? I wonder if my PNG file is causing the issue?


p.s. When I say I see nothing, I mean its a black image with no text.

From: ffmpeg-user <ffmpeg-user-bounces at ffmpeg.org> on behalf of Carl Eugen Hoyos <ceffmpeg at gmail.com>
Sent: Monday, February 5, 2018 7:26:37 AM
To: FFmpeg user questions
Subject: Re: [FFmpeg-user] Alpha Channel QT with SubTitles

2018-01-17 17:34 GMT+01:00 Gandharv Bhagat <fradac at hotmail.com>:

> Thanks for the frame rate multiplier correction, will make the change.
> As for the file, I am checking in FCP 7. When alpha type is set to
> ‘none/ignore’ I see a white background and white text and the drop
> shadow. When the alpha type is set to ‘straight’, ‘black’, or ‘white’
> I don’t see anything.

I wonder how it is possible not to "see anything" on a video screen...

The most relevant question from our point-of-view is if the following
command (or a variant) indicates transparency in your video:
$ ffmpeg -f lavfi -i testsrc=s=hd1080 -i Subs2.mov -filter_complex
overlay -qscale 2 -vcodec mpeg4 out.mov

The issue hitting you may be that a flag has to be set in the mov
file or the video bitstream to indicate the type of the transparency.

Please do not top-post here, Carl Eugen
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