Pure alpha Video + Text

[Angel Martin]

Dear all,

Any idea about how to get a pure alpha video except for the textoverlay
area?

Best,

Angel

2011/4/29 Angel Martin <amartin at vicomtech.org>

> Dear all,
>
> I want to mix (videomixer) a multimedia source (video or image) with a text
> (textoverlay) with gnlcomposition to insert the text in the proper time.
>
> 1) At the beginning I used a gnloperation to insert the textoverlay inside
> a bin with a textoverlay. But problems arised when I had a lot of images and
> texts. It was not possible to get a desired layout. Because to get a correct
> functionality the priority has to be low and unique (according to my tests).
>
> 2) So, I am trying to insert each text as a video with an alpha channel.
>
> I achieved it with a gnlsource with a bin that contains a videotestsrc with
> green pattern and an alpha element to remove the green part with an alpha
> channel but in some borders of the image there is a residual line.
> videotestsrc pattern=5 ! ffmpegcolorspace ! textoverlay text="HELLOWORLD" !
> *alpha prefer-passthrough=TRUE method=1* ! video/x-raw-yuv,
> framerate=\(fraction\)25/1, format=\(fourcc\)AYUV, width=640, height=480 !
> ffmpegcolorspace
>
>
> And for example in this case: textoverlay text="HELLOWORLD"
> color=4278255360 (0xff00ff00) The text is also "alphaed". So not completely
> solved yet. Moreover, the alpha module inserts a residual line and
> computational waste.
>
> 3) So I want a pure alpha video with a text to mix it with an image.
>
> This is a test pipeline where the videotestsrc has directly a 0x00000000
> (ARGB value = pure alpha black = transparent) with a text overlay with color
> 0xff00ff00 (ARGB value = solid green).
>
> gst-launch videomixer name=mix sink_0::zorder=3 sink_1::zorder=2 !
> ffmpegcolorspace ! timeoverlay ! autovideosink videotestsrc pattern=17
> foreground-color=0 ! textoverlay text="HELLOWORLD" color=4278255360
> shaded-background=TRUE ! video/x-raw-yuv, framerate=\(fraction\)25/1,
> format=\(fourcc\)AYUV, width=640, height=480 ! ffmpegcolorspace ! mix.sink_0
> filesrc location=~/image.jpg ! decodebin ! queue ! ffmpegcolorspace !
> videoscale ! imagefreeze2 ! alpha prefer-passthrough=TRUE ! video/x-raw-yuv,
> framerate=\(fraction\)25/1, format=\(fourcc\)AYUV, width=640, height=480 !
> ffmpegcolorspace ! mix.sink_1
>
> However the textoverlay plugin doesn't overwrite its alpha value and the
> text doesn't appear anyplace. It seems the text inherits the alpha value of
> the videotestsrc.
>
> If a change the videotestsrc to get semitransparent color=2147483648
> (0x80000000) (ARGB semitransparent black) the text appears but again It
> seems the text inherits the alpha value of the videotestsrc.
>
> gst-launch videomixer name=mix sink_0::zorder=3 sink_1::zorder=2 !
> ffmpegcolorspace ! timeoverlay ! autovideosink videotestsrc pattern=17
> foreground-color=2147483648 ! textoverlay text="HELLOWORLD" color=4278255360
> shaded-background=TRUE ! video/x-raw-yuv, framerate=\(fraction\)25/1,
> format=\(fourcc\)AYUV, width=640, height=480 ! ffmpegcolorspace ! mix.sink_0
> filesrc location=~/image.jpg ! decodebin ! queue ! ffmpegcolorspace !
> videoscale ! imagefreeze2 ! alpha prefer-passthrough=TRUE ! video/x-raw-yuv,
> framerate=\(fraction\)25/1, format=\(fourcc\)AYUV, width=640, height=480 !
> ffmpegcolorspace ! mix.sink_1
>
> I tryed to insert alphacolor elements and introduce different schemes of
> ffmpegcolorspaces and capsfilter, and I also checked that the zorder of the
> videomixer is right, but I haven't achieved the expected result.
>
> Any ideas?
>
> Thank you in advance.
>
> Best Regards.
>
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