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Make transparent a specific color inside a video

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megabug

Make transparent a specific color inside a video

Hi,

I have two videos:
1 - An animated "title" text video (letters moving around with a complex schema) with a black background.
2 - Another video taken with a camera

Using libpigment, I tried to put the video 1 over video 2 but the black background of titles is not transparent and covers the second video. If I try to change alpha value on the whole video the black will be mixed with the second video making it darker.

Is it possible to make transparent a only part of the video with a specific color (the black on the first video in my case)?

--
megabug

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Kapil Agrawal

Re: Make transparent a specific color inside a video

Probably videobox and videomixer may fix it

-kapil

On Fri, Oct 30, 2009 at 4:55 PM, megabug <[hidden email]> wrote:

Hi,

I have two videos:
1 - An animated "title" text video (letters moving around with a complex schema) with a black background.
2 - Another video taken with a camera

Using libpigment, I tried to put the video 1 over video 2 but the black background of titles is not transparent and covers the second video. If I try to change alpha value on the whole video the black will be mixed with the second video making it darker.

Is it possible to make transparent a only part of the video with a specific color (the black on the first video in my case)?

--
megabug

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megabug

Re: Make transparent a specific color inside a video

On Friday 30 October 2009 12:59:17 Kapil Agrawal wrote:
> Probably videobox and videomixer may fix it
>
> -kapil

No, as I stated before in my email, changing the whole frame alpha value is not useful in my case.

Anyway I managed to find the solution myself: the "alpha" plugin works and provides a chroma-key feature that is exacly what I needed.

Now I have another problem: PgmImageSink (in pigment library) refuses to receive a stream with Alpha channel in it.

filesrc -> decodebin -> alpha -> pgmimagesink (doesn't work)

If I put an ffmpegcolorspace, the pipeline runs successfully but the alpha channel is filtered.

filesrc -> decodebin -> alpha -> ffmpegcolorspace -> pgmimagesink
(works but ffmpegcolorspace removes the alpha channel)

Even using capsfilter to force a colorspace with alpha channel won't work.
I think that the problem is in pgmimagesink, but any suggestions are welcome!

Bye
--
megabug

Jan Schmidt-6

Re: Make transparent a specific color inside a video

In reply to this post by megabug

On Fri, 2009-10-30 at 12:25 +0100, megabug wrote:

>
> Hi,
>
>
>
> I have two videos:
> 1 - An animated "title" text video (letters moving around with a
> complex schema) with a black background.
> 2 - Another video taken with a camera
>
>
>
> Using libpigment, I tried to put the video 1 over video 2 but the
> black background of titles is not transparent and covers the second
> video. If I try to change alpha value on the whole video the black
> will be mixed with the second video making it darker.

You can use the 'alpha' element to perform 'green-screening',
selectively converting a given color range to transparency. It would be
better/more efficient overall to use a format for the titles that
supports an alpha channel already, however - such as PNG files.

Regards,
Jan.

>
>
>
> Is it possible to make transparent a only part of the video with a
> specific color (the black on the first video in my case)?
>
>
>
> --
> megabug
>
> ------------------------------------------------------------------------------
> Come build with us! The BlackBerry(R) Developer Conference in SF, CA
> is the only developer event you need to attend this year. Jumpstart your
> developing skills, take BlackBerry mobile applications to market and stay
> ahead of the curve. Join us from November 9 - 12, 2009. Register now!
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--
Jan Schmidt <[hidden email]>

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palani-3

videomixer

Hi,

I tried the following command:
gst-launch rtspsrc location=rtsp://IP/test.mp4 ! rtph264depay !
mfw_vpudecoder ! videobox ! videomixer ! videobox ! mfw_v4lsink

I am getting the following errors.

(gst-launch-0.10:1883): GStreamer-CRITICAL **:
gst_mini_object_is_writable: assertion `mini_object != NULL' failed

(gst-launch-0.10:1883): GStreamer-CRITICAL **:
gst_mini_object_is_writable: assertion `mini_object != NULL' failed

(gst-launch-0.10:1883): GStreamer-CRITICAL **:
gst_mini_object_is_writable: assertion `mini_object != NULL' failed

(gst-launch-0.10:1883): GStreamer-CRITICAL **:
gst_mini_object_is_writable: assertion `mini_object != NULL' failed

If I try without videomixer, I did not get this error and video plays
properly.

Can anyone help me?

Regards,
Palanivel

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Stefan Sauer

Re: videomixer

[hidden email] schrieb:

> Hi,
>
> I tried the following command:
> gst-launch rtspsrc location=rtsp://IP/test.mp4 ! rtph264depay !
> mfw_vpudecoder ! videobox ! videomixer ! videobox ! mfw_v4lsink
>
> I am getting the following errors.
>
> (gst-launch-0.10:1883): GStreamer-CRITICAL **:
> gst_mini_object_is_writable: assertion `mini_object != NULL' failed
>
> (gst-launch-0.10:1883): GStreamer-CRITICAL **:
> gst_mini_object_is_writable: assertion `mini_object != NULL' failed
>
> (gst-launch-0.10:1883): GStreamer-CRITICAL **:
> gst_mini_object_is_writable: assertion `mini_object != NULL' failed
>
> (gst-launch-0.10:1883): GStreamer-CRITICAL **:
> gst_mini_object_is_writable: assertion `mini_object != NULL' failed
>
> If I try without videomixer, I did not get this error and video plays
> properly.
>
> Can anyone help me?
>

G_DEBUG="fatal_warnings" gdb --args gst-launch rtspsrc
location=rtsp://IP/test.mp4 ! rtph264depay ! mfw_vpudecoder ! videobox !
videomixer ! videobox ! mfw_v4lsink

inside gdb "run" and when it breaks "bt", then you got a backtrace and
can make a fix.

Stefan

> Regards,
> Palanivel
>
>
>
> ------------------------------------------------------------------------------
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>