I.MX6 - gstreamer-imx and usb webcam support

Following on from my previous post about gstreamer-imx, this blog covers hooking a usb webcam using the gstreamer-imx plugins. It starts with creating simple pipeline for screen output, next is a pipeline for time lapse video recording. We then progress to streaming to VLC and finally implementing a simple rtsp server. Below is video demonstrating a simple RTSP server running on a AR6MXQ streaming to VLC. The webcam is pointing at the screen and streams the output (720p @10fps). We launch a VLC client window which is located in the lower right side of the same screen (unfortunately this causes an echo effect). As you will see any activity on the screen is streamed to the VLC client window (lower right) albeit with a delay.

The webcam in question was a microsoft HD-3000 which in theory is capable of 720p at 30fps. As with most webcams (which don't encode H264) it outputs YUYV (YUY2) and more importantly MJPEG. On linux you can easily determine what your webcam capabilities are by launching  v4l2-ctl, eg:

v4l2-ctl --list-formats-ext

This post provides a guide to what is possible with a gstreamer-imx plugins and the examples provided should not be treated as production ready. I'm assuming the examples will work on other usb webcams and or potentially other v4l2 devices. However the examples may require alterations depending on your webcam and it's capabilities, therefore background reading on gstreamer is recommended.

Testing was conducted on debian jessie and the target device was a AR6MXQ board provided by BCM Advanced Research. The examples should run on most imx6 devices as there is no device specific dependencies.

While testing with the HD-3000, the webcam  occasionally stop sending a stream if I configured the wrong resolution. The workaround was to unplug the device or reset the usb port  (replace '1-1.3' with the correct usb host and port id for your webcam) eg :

echo 1-1.3 > /sys/bus/usb/drivers/usb/unbind
echo 1-1.3 > /sys/bus/usb/drivers/usb/bind

Output to screen

Now back to the webcam, first step was getting output displayed to the screen. This requires reading the v4l2 source and converting the input so that is compatible with imxeglvivsink. Initial testing revealed decoding MPEG from the webcam performed significantly better than decoding YUY2. Another issue encountered (thanks to Carlos) was imxvpudec outputting Y42B something imeglvivsink currently can't cope with hence the inclusion of imxipuvideotransform element. So here is the final pipeline (webcam input is MPEG 720p at 30fps) :


gst-launch-1.0 v4l2src ! 'image/jpeg,width=1280,height=720,framerate=30/1' ! im
xvpudec ! imxipuvideotransform ! imxeglvivsink sync=false

CPU usage for the above was around 10%, while for YUY2 (720p at 10fps) it rises to 25% with this pipeline:

gst-launch-1.0 v4l2src ! 'video/x-raw,width=1280,height=720,framerate=10/1' ! imxipuvideotransform ! imxeglvivsink sync=false

Simple time lapsed video recording

Now lets implement a simple timelapsed video recorder that outputs to file and screen. I limited to the input MPEG stream to 10fps, reduced the bitrate  and encoded as h264 to reduce the output file size. Additional CPU load occurs due to the inclusion of the clockoverlay element, without the element it is difficult to know when the recording was taken.  Without this clockoverlay element CPU load is < 10%.

gst-launch-1.0 v4l2src ! 'image/jpeg,width=1280,height=720,framerate=10/1' ! imx
vpudec ! imxipuvideotransform ! clockoverlay time-format="%Y/%m/%d %H:%M:%S" ! tee name=splitter ! queue ! imxvpuenc_h264 bitrate=1024 ! filesink location=test .mp4 splitter. ! queue ! imxeglvivsink sync=false

The above pipeline generates approximately 400Mb per hour so probably not practical for production use.

Streaming to VLC

To enable streaming to VLC we need to create a 'sdp' file, this instruction VLC to act as a rtp server, below are the contents of the file:

v=0
s=GStreamer
m=video 5000 RTP/AVP 96
c=IN IP4 127.0.0.1
a=type:broadcast
a=rtpmap:96 H264/90000
a=fmtp:96

Save the contents to file eg 'imx6.sdp' and launch VLC,  because there is no h/w acceleration for VLC on the imx6, VLC was running on a PC :

vlc --no-audio imx6.sdp

On the imx6, we are a rtp client submitting h264 payloads to the VLC server (note the inclusion of the host/ip address of the PC) :

gst-launch-1.0 -v v4l2src ! 'image/jpeg,width=1280,height=720,framerate=10/1' !
imxvpudec ! imxipuvideotransform ! imxvpuenc_h264 bitrate=1024 ! rtph264pay ! udpsink host=<host/ip of PC> port=5000

Simple RTSP server

And lastly, lets try running an rtp server. Fortunately there is an additional gstreamer plugin (gst-rtsp-server) with rtp support that includes an example test server. The downside is that it needs to be built from sources. You will need to checkout the 1.1.90 tag and build (similar to gstreamer-imx). Once built we can launch the example test server and pass it a pipeline similar to that used when outputting to screen (you need to export the library path so that libgstrtspserver-1.0.so is found) eg:

export ./gst-rtsp-server/gst/rtsp-server/.libs
cd ./gst-rtsp-server/examples/.libs/

./test-launch '(v4l2src ! 'image/jpeg,width=1280,height=720,framerate=10/1' !imxvpudec ! imxipuvideotransform ! imxvpuenc_h264 ! rtph264pay name=pay0 pt=96 )' 

The test server listens on port 8554 therefore the rtsp URL is

rtsp://<host/ip of imx6>:8554/test

You can test by launching VLC and opening a 'Network Stream' to the URL. While streaming the CPU load on the imx6 hovered around 60%. Given this is example code it should be possible to optimise the pipeline/code to bring down this figure.

I.MX6 - gstreamer-imx

gstreamer-imx is set of gstreamer 1.0 imx6 video plugins principally developed by Carlos Giani a.k.a dv_ (great work!). Once stable these plugins "hopefully" will supersede the Freescale BSP gstreamers 0.10 plugins which are showing their age given that gstreamer 0.10 is longer maintained.

The main driver for this work was to get a usb webcam streaming via these plugins this will be covered in the next post. In meantime below are build instructions for deploying the latest code to the debian rootfs if you fancy experimenting.  I'm finding the debian jessie build useful to jump start prototype development on the imx6 mainly due to the availability of prebuilt packages.

Here is a short video demonstrating the use of color key along with the imxipusink to hide/view video within XFCE. The video only appears for the color key 'black' hence it is visible in the terminal windows and menu. The test device was a AR6MXQ board provide by BCM Advanced Research. As a designer/provider of industrial motherboards BCM have done a good job with their first feature rich ARM development board.

The current debian rootfs already includes an older build of the gstreamer-imx plugins. Upgrading these to a newer release is fairly trivial, you can build the latest sources natively on debian as follows:

1. Remove the existing plugins

 rm /usr/lib/arm-linux-gnueabihf/gstreamer-1.0/libgstimxipu.so 
 rm /usr/lib/arm-linux-gnueabihf/gstreamer-1.0/libgstimxvpu.so 
 rm /usr/lib/arm-linux-gnueabihf/gstreamer-1.0/libgstimxeglvivsink.so 

 rm /usr/lib/libgstimxcommon.so 
 rm /usr/lib/libgstimxcommon.so.0 
 rm /usr/lib/libgstimxcommon.so.0.9.1 

2. Build lastest sources

 git clone git://github.com/Freescale/gstreamer-imx.git  
 cd gstreamer-imx  
 ./waf configure --prefix=usr --kernel-headers=/usr/include  
 ./waf  
 ./waf install  

3. Deploy plugins

 cp usr/lib/gstreamer-1.0/libgstimxipu.so /usr/lib/arm-linux-gnueabihf/gstreamer-1.0  
 cp usr/lib/gstreamer-1.0/libgstimxvpu.so /usr/lib/arm-linux-gnueabihf/gstreamer-1.0  
 cp usr/lib/gstreamer-1.0/libgstimxeglvivsink.so /usr/lib/arm-linux-gnueabihf/gstreamer-1.0  
 cp usr/lib/gstreamer-1.0/libgstimxv4l2src.so /usr/lib/arm-linux-gnueabihf/gstreamer-1.0  
 cp usr/lib/libgstimxcommon.so.0.9.5 /usr/lib  
 cd /usr/lib  
 ln -s libgstimxcommon.so.0.9.5 libgstimxcommon.so.0  
 ln -s libgstimxcommon.so.0.9.5 libgstimxcommon.so  

4. Reboot

5. Verify the plugins are present

 root@debian-imx6:~# gst-inspect-1.0 | grep imx  
 imxipu: imxipuvideotransform: Freescale IPU video transform element  
 imxipu: imxipusink: Freescale IPU video sink  
 imxvpu: imxvpudec: Freescale VPU video decoder  
 imxvpu: imxvpuenc_h263: Freescale VPU h.263 video encoder  
 imxvpu: imxvpuenc_h264: Freescale VPU h.264 video encoder  
 imxvpu: imxvpuenc_mpeg4: Freescale VPU MPEG-4 video encoder  
 imxvpu: imxvpuenc_mjpeg: Freescale VPU motion JPEG video encoder  
 imxeglvivsink: imxeglvivsink: Freescale EGL video sink  
 imxv4l2src: imxv4l2src: V4L2 CSI Video Source  

6. Test video playback (under X11)

 gst-launch-1.0 playbin uri=file://<video file> video-sink=imxeglvivsink  

Unfortunately the elements/sinks aren't documented so you may need to refer to the source code to determine features or properties. There is also a new plugin for CSI camera sources (imxv4l2src) provided by  Philip Craig.