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v4l2src and a usb tv tuner

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Dimitar Popov
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v4l2src and a usb tv tuner

Dimitar Popov
Hi all,

I'm having problem using my usb tv tuner with gstreamer. I tried the following
with gst-launch-0.10:

$ gst-launch-0.10 v4l2src device=/dev/video1 ! autovideosink

Setting pipeline to PAUSED ...
ERROR: Pipeline doesn't want to pause.
ERROR: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Device
'/dev/video1' cannot capture at 720x576
Additional debug info:
gstv4l2object.c(2093): gst_v4l2_object_set_format ():
/GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
Call to S_FMT failed for YV12 @ 720x576: Invalid argument
Setting pipeline to NULL ...
Freeing pipeline ...

Then I checked what properties v4l2 reports:

$ v4l2-ctl -d /dev/video1 --all

and noticed that the tv tuner uses YUY2 (also known as YUYV) instead of YV12
as detected by GST:

Format Video Capture:
        Width/Height  : 720/576
        Pixel Format  : 'YUYV'
        Field         : Interlaced
        Bytes per Line: 1440
        Size Image    : 829440
        Colorspace    : SRGB
Format Video Output:
        Width/Height  : 720/576
        Pixel Format  : 'YUYV'
        Field         : Interlaced
        Bytes per Line: 1440
        Size Image    : 829440
        Colorspace    : SRGB

So I decided to explicitly tell GST to use YUY2:

gst-launch-0.10  v4l2src device=/dev/video1 ! video/x-raw-
yuv,format=\(fourcc\)YUY2 ! ffmpegcolorspace ! autovideosink

but got:

Setting pipeline to PAUSED ...
ERROR: Pipeline doesn't want to pause.
ERROR: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Could not
negotiate format
Additional debug info:
gstbasesrc.c(2778): gst_base_src_start ():
/GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
Check your filtered caps, if any
Setting pipeline to NULL ...
Freeing pipeline ...

Adding --gst-debug=v4l2:5 revealed that GST recognises YU12, YV12, BGR3 and
RGB3 pixel formats:

v4l2 gstv4l2object.c:1038:gst_v4l2_object_fill_format_list:<v4l2src0>   YU12
(emulated)
v4l2 gstv4l2object.c:1038:gst_v4l2_object_fill_format_list:<v4l2src0>   YV12
(emulated)
v4l2 gstv4l2object.c:1038:gst_v4l2_object_fill_format_list:<v4l2src0>   BGR3
(emulated)
v4l2 gstv4l2object.c:1038:gst_v4l2_object_fill_format_list:<v4l2src0>   RGB3
(emulated)

The version of gstreamer is 0.10.32 and the version of gst-plugins-good is
0.10.27 from the archlinux x86_64 repo.

I've attached the debug output from gst-launch and the output of v4l2-ctl, but
if any other information is needed I'll provided of course.

I'm not an expert in the field so I have only a vague notion of what
colorspace and pixel formats are, so please, execuse me, if I've done some
stupid mistake :)

Thanks in advance for the help!

Dimitar

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Andrey Nechypurenko-2
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Re: v4l2src and a usb tv tuner

Andrey Nechypurenko-2
Hi,

> gst-launch-0.10  v4l2src device=/dev/video1 ! video/x-raw-
> yuv,format=\(fourcc\)YUY2 ! ffmpegcolorspace ! autovideosink

The first thing which I would suggest is to explicitly provide frame
width, height and framerate in your caps filter. Something like this:

gst-launch-0.10  v4l2src device=/dev/video1 !
video/x-raw-yuv,format=\(fourcc\)YUY2,width=720,height=576,framerate=\(fraction\)25/1
! ffmpegcolorspace ! autovideosink

I am not sure about frame rate. Maybe 30/1 is the right value. It
depends on your camera.

HTH,
Andrey.
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Stefan Sauer
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Re: v4l2src and a usb tv tuner

Stefan Sauer
In reply to this post by Dimitar Popov
On 28.02.2011 00:41, Dimitar Popov wrote:

> Hi all,
>
> I'm having problem using my usb tv tuner with gstreamer. I tried the following
> with gst-launch-0.10:
>
> $ gst-launch-0.10 v4l2src device=/dev/video1 ! autovideosink
>
> Setting pipeline to PAUSED ...
> ERROR: Pipeline doesn't want to pause.
> ERROR: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Device
> '/dev/video1' cannot capture at 720x576
> Additional debug info:
> gstv4l2object.c(2093): gst_v4l2_object_set_format ():
> /GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
> Call to S_FMT failed for YV12 @ 720x576: Invalid argument
> Setting pipeline to NULL ...
> Freeing pipeline ...
>
> Then I checked what properties v4l2 reports:
>
> $ v4l2-ctl -d /dev/video1 --all
>
> and noticed that the tv tuner uses YUY2 (also known as YUYV) instead of YV12
> as detected by GST:
>
> Format Video Capture:
>         Width/Height  : 720/576
>         Pixel Format  : 'YUYV'
>         Field         : Interlaced
>         Bytes per Line: 1440
>         Size Image    : 829440
>         Colorspace    : SRGB
> Format Video Output:
>         Width/Height  : 720/576
>         Pixel Format  : 'YUYV'
>         Field         : Interlaced
>         Bytes per Line: 1440
>         Size Image    : 829440
>         Colorspace    : SRGB
>
> So I decided to explicitly tell GST to use YUY2:
>
> gst-launch-0.10  v4l2src device=/dev/video1 ! video/x-raw-
> yuv,format=\(fourcc\)YUY2 ! ffmpegcolorspace ! autovideosink
>
> but got:
>
> Setting pipeline to PAUSED ...
> ERROR: Pipeline doesn't want to pause.
> ERROR: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Could not
> negotiate format
> Additional debug info:
> gstbasesrc.c(2778): gst_base_src_start ():
> /GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
> Check your filtered caps, if any
> Setting pipeline to NULL ...
> Freeing pipeline ...
>
> Adding --gst-debug=v4l2:5 revealed that GST recognises YU12, YV12, BGR3 and
> RGB3 pixel formats:
>
> v4l2 gstv4l2object.c:1038:gst_v4l2_object_fill_format_list:<v4l2src0>   YU12
> (emulated)
> v4l2 gstv4l2object.c:1038:gst_v4l2_object_fill_format_list:<v4l2src0>   YV12
> (emulated)
> v4l2 gstv4l2object.c:1038:gst_v4l2_object_fill_format_list:<v4l2src0>   BGR3
> (emulated)
> v4l2 gstv4l2object.c:1038:gst_v4l2_object_fill_format_list:<v4l2src0>   RGB3
> (emulated)
>
> The version of gstreamer is 0.10.32 and the version of gst-plugins-good is
> 0.10.27 from the archlinux x86_64 repo.
>
> I've attached the debug output from gst-launch and the output of v4l2-ctl, but
> if any other information is needed I'll provided of course.

Current git has a fix for interlaced v4l2 sources which could fix your
problem.

Stefan

> I'm not an expert in the field so I have only a vague notion of what
> colorspace and pixel formats are, so please, execuse me, if I've done some
> stupid mistake :)
>
> Thanks in advance for the help!
>
> Dimitar
>
>
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

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