V4L2-GFX
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[edit] V4L2-GFX
This is a driver which allows a V4L2 aware components for e.g. a Gstreamer video decoder to propagate video buffer data to a texture stream aware GL application.
An overview of the current architecture is given here.
[edit] Software Components
[edit] V4L2-GFX driver
This is a linux kernel driver/module. The driver acts as a V4L2 video capture device and presents an ioctl API (largely) identical to the OMAP V4L2 interface to hardware overlays.
[edit] Source code
Currently the driver is in the kernel/omap staging area here: http://review.omapzoom.org/#change,7685
In the Android kernel the driver sources is located in {kernelroot}/drivers/media/video/omapgfx/
[edit] Video renderer
[edit] GStreamer
If you have a working Gstreamer setup which can decode video to overlay devices (e.g. /dev/video1) then broadly speaking all you need to do is use the V4L2-GFX device node /dev/video100.
[edit] V4L2-GFX unit test
v4l2_gfx_client is the unit test for the V4L2-GFX driver. The final part of the unit test involves copying raw NV12 video frames to the V4L2-GFX device so can simulate the activity of a render, although this will be less performant than h/w accelerated decoding because an ARM memcopy is involved.
Unfortunately we currently only distribute the v4l2_gfx_client as part of the DDK. The reason isn't technical or legal, it's just that we don't have a good place to distribute this code at the moment.
[edit] Texture streaming applications
In order to display the video frames captured by the V4L2-GFX driver you need an appropriate GL application which uses IMG's texture streaming extensions.
We have 2 apps as follows.
[edit] Gles1TexturePlayer
This app renders a flat video surface.
Note that on OMAP4/SGX DDK 3977 that this app causes an SGX crash which has been reported to IMG.
[edit] Gles2TexturePlayer
This app renders a rotating video surface.
[edit] Integrating the V4L2-GFX driver
[edit] Build
Prerequisites: You have a kernel (or patched the kernel) with the V4L2-GFX driver in it (See 'Source code').
; This worked on the Android Froyo 2.6.35 environment make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi-; Where is your hardware target e.g. android_4430_defconfig
Inspect your .config file and look for the CONFIG_VIDEO_OMAP_GFX entry:
CONFIG_VIDEO_OMAP_GFX=m
The above means V4L2-GFX will be built as a kernel module
To configure V4L2-GFX driver for e.g. build as part of the kernel:
make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi- menuconfig
Select: Device Drivers ---> Multimedia support ---> Video capture adapters ---> OMAP V4L2-GFX driver
Alternatively, modify the board configuration file directly:
; Edit arch/arm/configs/android_4430_defconfig vi arch/arm/configs/android_4430_defconfig ; V4L2-GFX in the kernel: CONFIG_VIDEO_OMAP_GFX=y
The complete build sequence using a 4430SDP Android environment as an example:
make CROSS_COMPILE=arm-none-linux-gnueabi- distclean make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi- android_4430_defconfig make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi- uImage make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi- modules
[edit] Configuration
If V4L2-GFX is built as part of the kernel you should see a device node:
/dev/video100
Ensure your application has the relevant permissions to access the device.
chmod 666 /dev/video100
(On Android, you may wish to do this chmod in the Android file-system init.rc, you'll typically see this done for other /dev/video device nodes on OMAP targets).
# change permissions for Overlay chmod 0777 /dev/video1 chmod 0777 /dev/video2 chmod 0777 /dev/video3 ; V4L2-GFX for texture streaming chmod 0777 /dev/video100
[edit] Kernel modules
If built as a kernel module the built module will be here:
drivers/media/video/omapgfx/gfx_vout_mod.ko
You'll need to get that .ko onto the device file-system in whatever method you prefer.
[edit] Texture streaming demo with the v4l2_gfx_client unit test (Android)
Start the Gles2TexturePlayer application from the SGX DDK tests (icon).
Select 'Launch stream'
The application will prompt to start a video rendering to V4L2-GFX.
Start the v4l2_gfx_client application from an adb shell console.
You will see a constantly repeating series of frames rendered to the screen.
[edit] V4L2-GFX feature backlog
| Title | Description | Status |
| tbd | tbd | tbd |
