Adaptive Bitrate Streaming using GStreamer

Gateworks’ SBCs are widely used for streaming audio and video over the network via Ethernet, 802.11 WiFi, or 4G LTE Cellular. Networks are dynamic, whether from network load, RF interference or signal strength thus throughput will vary requiring intelligent and flexible applications to adjust as necessary.

Adaptive Bitrate Streaming is the concept of adjusting the quality of video and/or audio depending on the quality of the network connection or server load. This type of technology is widely implemented throughout technology today, evident in streaming services like Netflix and YouTube.

​Gateworks created an example GStreamer application named gst-variable-rtsp-server. This application includes a mechanism for auto-adjusting the encoding bitrate depending on the number of clients connected to the server.

gst-variable-rtsp-server can change either the quant-param or the bitrate parameters of the imxvpuenc_h264 encoder. The quant-param will only be used if the pipeline is set to Variable Bitrate mode (VBR). This can be accomplished by passing in the -b 0 flag to the program. Otherwise, gst-variable-rtsp-server will change the bitrate of the stream.

The algorithm used to change both bitrate and quant-param are based on the --steps input (defaulted to 5). For example, if using the default steps value of 5, if the min bitrate was 500 and max bitrate was 2000, it would take 5 clients to adjust from the highest to the lowest quality.

In the below example, the rtsp server was configured to degrade from 10mbps to 400kbps bitrate within 5 steps. Please see below for our results.

gst-variable-rtsp-server --steps=5 --max-bitrate=10000 --min-bitrate=400 --src-element=imxv4l2videosrc --video-in=/dev/video0


For higher resolution images of the above, please view here (10Mbps), here (2.8Mbps), and here (400Kbps).

For more information and sample GStreamer pipelines, please visit our Software Wiki Pages:

GStreamer Compositing for Streaming H.264 Video

Gateworks recently featured a blog in which 8 video cameras were connected to a Gateworks Ventana SBC and then displayed on a HDMI monitor. This is useful for localized applications. For remote applications there is another solution.

Remote applications require streaming the multiple video streams over the network (Ethernet or WiFi). For bandwidth efficiency, all camera inputs can be joined together into a single frame and then transmitted across the network.


To join all the streams into a single frame, a software element of GStreamer called a compositor is used. Older versions of the compositor relied on the CPU and caused choppy video. Gateworks recently started using gstreamer-imx which contains a hardware accelerated compositor which is far superior. With this compositor, each stream can be positioned on the frame and then linked to a RTSP stream in the H.264 format.

An example is shown with two Gateworks Ventana SBCs that are on the same network.

Start the following pipeline on the SBC with the cameras connected:

gst-variable-rtsp-server -u \
 "imxv4l2videosrc device=/dev/video2 queue-size=55 ! queue2 ! c.sink_0 \
 imxv4l2videosrc device=/dev/video3 queue-size=55 ! queue2 ! c.sink_1 \
 imxv4l2videosrc device=/dev/video4 queue-size=55 ! queue2 ! c.sink_2 \
 imxv4l2videosrc device=/dev/video5 queue-size=55 ! queue2 ! c.sink_3 \
 imxv4l2videosrc device=/dev/video6 queue-size=55 ! queue2 ! c.sink_4 \
 imxv4l2videosrc device=/dev/video7 queue-size=55 ! queue2 ! c.sink_5 \
 imxv4l2videosrc device=/dev/video8 queue-size=55 ! queue2 ! c.sink_6 \
 imxv4l2videosrc device=/dev/video9 queue-size=55 ! queue2 ! c.sink_7 \
 imxg2dcompositor name=c background-color=0xffffff \
 sink_0::xpos=0 sink_0::ypos=0 sink_0::width=320 sink_0::height=360 sink_0::fill_color=0x00000000 \
 sink_1::xpos=320 sink_1::ypos=0 sink_1::width=320 sink_1::height=360 sink_1::fill_color=0x00000000 \
 sink_2::xpos=640 sink_2::ypos=0 sink_2::width=320 sink_2::height=360 sink_2::fill_color=0x00000000 \
 sink_3::xpos=960 sink_3::ypos=0 sink_3::width=320 sink_3::height=360 sink_3::fill_color=0x00000000 \
 sink_4::xpos=0 sink_4::ypos=360 sink_4::width=320 sink_4::height=360 sink_4::fill_color=0x00000000 \
 sink_5::xpos=320 sink_5::ypos=360 sink_5::width=320 sink_5::height=360 sink_5::fill_color=0x00000000 \
 sink_6::xpos=640 sink_6::ypos=360 sink_6::width=320 sink_6::height=360 sink_6::fill_color=0x00000000 \
 sink_7::xpos=960 sink_7::ypos=360 sink_7::width=320 sink_7::height=360 sink_7::fill_color=0x00000000 \
 ! queue2 ! video/x-raw, width=1280, height=720 ! imxipuvideotransform \
 ! imxvpuenc_h264 bitrate=20000 ! rtph264pay name=pay0 pt=96"

Then, on the receiving board that is connected to an HDMI display, start the following pipeline with the actual IP address (example IP below) of the board with the cameras:

gst-launch-1.0 rtspsrc location=rtsp:// latency=100 ! \
queue2 ! decodebin ! autovideosink

For more information and code examples, please visit the related Gateworks Software Wiki links below:


i.MX6 GStreamer-imx Plugins – Tutorial & Example Pipelines

Gateworks would like to announce the support of the GStreamer-imx plugins starting with Yocto 1.8 on the Ventana family of Single Board Computers.


Gateworks, the leading supplier of Powerful ARM based Single Board Computer solutions using the Freescale i.MX6, has invested countless engineering hours researching and mastering GStreamer for the i.MX series of processors. Gateworks would like to share this GStreamer research with the rest of the i.MX community of developers!

There are two main versions of GStreamer used on the i.MX6 processor:0.10 and 1.0. Version 1.0 is now the latest standard.

The i.MX6 processor has hardware blocks such as the IPU (image processing unit), VPU (video processing unit), and GPU (graphical processing unit). The main advantage of using these hardware blocks is that there is no CPU cost for decoding/encoding a stream because another hardware block in the i.MX6 takes care of it. This leaves the CPU free to deal with other programs etc.

The GStreamer app works with ‘plugins’. A plugin comprises of elements that can do work on a media stream. For example, the imxvpudec is a VPU based decoder plugin.

This post is specifically about the plugins. There are different versions and sets of plugins available.

Gateworks has chosen to use the GStreamer-imx plugins for the following reasons:

  • Open Source Development model: The project is on github and is very active
  • The main developer has been a GStreamer contributer for some time now and is very active in the GStreamer community
  • The source is very well documented and easy to follow
  • Things are done in a very standard GStreamer way

Plugin List

For a thorough description of each plugin, why and how to use it, please visit the Gateworks Software Wiki GStreamer Page

The following is a list of plugins provided by the latest version of gstreamer-imx (0.11.0)

Type Plugin(s) Element(s) Comments
Audio Decoder imxaudio imxuniaudiodec Uses i.MX uniaudio codecs for decoding
Audio Encoder imxaudio imxmp3audioenc Uses i.MX for MP3 audio encoding
Device Sources imxv4l2video imxv4l2videosrc Get camera source via v4l2
Video Decoder imxvpu imxvpudec VPU Based decoder
Video Encoder imxvpu imxvpuenc_mjpeg; imxvpuenc_mpeg4; imxvpuenc_h264; imxvpuenc_h263 VPU Based encoders
Video Render (sink) imxg2d; imxpxp; imxeglvivsink; imxipu imxg2dvideosink; imxpxpvideosink; imxeglvivsink; imxipuvideosink g2d1, ipu1, pxp2, and egl (overlay) video sinks
Video Converter imxg2d; imxpxp; imxipu imxg2dvideotransform; imxpxpvideotransform; imxipuvideotransform g2d, pxp, egl and ipu video filter/converter/scalars3
Video Compositing imxg2d; imxipu imxg2dcompositor, imxipucompositor gpu/ipu accelerated compositing

1. The g2d sink is very flexible in the types of input video it can take, but doesn’t have the ability to convert to as many formats as the IPU can. On the other hand, the IPU is very picky with it’s input (e.g. requiring a 1px offset) and the kernel driver is very undocumented, but as stated before, it can convert between many colorspace formats.
2. Note that the PXP sinks are only applicable to the i.mx6solo and i.mx6dl processors.
3. Please see note 1 above.

Plugin Example Pipeline

For example, to encode a video from a camera on /dev/video2 into h.264 and save it to a file:

#Take camera input /dev/video2, encode it to h264 at a bitrate of 10mbit/s (CBR) and save to a file.
gst-launch-1.0 imxv4l2videosrc device=/dev/video2 ! imxvpuenc_h264 bitrate=10000 ! filesink location=/tmp/file.mp4

Many more pipeline examples are described and listed on the Gateworks Software Wiki GStreamer Pipelines page


Using GStreamer 1.0 with the GStreamer-imx plugins is a powerful way to access and apply the multimedia capabilities of the Freescale i.MX6 processors on the Gateworks SBCs.

For more information, visit the Gateworks Software Wiki GStreamer Pipelines page

If there are other examples you would like to see, please add to the discussion!

H.264 Video Streaming over Network

The Gateworks Ventana Family of Single Board Computers is well suited for multimedia applications. The Freescale i.MX6 processor has hardware encoding and decoding making for very little processor overhead. To take advantage of this hardware decoding it is important to always use the ‘vpuenc’ and ‘vpudec’ gstreamer pipeline elements.

  • vpuenc – VPU (Video Processing Unit) encoder
  • vpudec – VPU (Video Processing Unit) decoder

It is also important to use a high compression video format such as H.264 which uses significantly less network bandwidth while retaining good quality. To use this, we encode by using the following pipeline element:

  • vpuenc codec=avc

When streaming over the network, TCP is a reliable protocol but often too stringent for video applications. UDP is often preferred so that even if packets are lost, the stream will continue without waiting for the lost packet. To use UDP, we use the udpsrc and udpsink pipeline elements.

Here is an example pipeline to stream live video over the network using two Ventana Single Board Computers. Be sure the two single board computers are on the same network and can ping each other. Both should also be running OpenEmbedded Yocto operating system. An analog video camera is connected to the video input on a Ventana board. Another Ventana board is connected to a HDMI monitor.

Start the server board pipeline first: (board with HDMI monitor connected)

root@ventana:~# gst-launch udpsrc port=9001 ! h264parse ! queue max-size-time=0 max-size-buffers=0 ! vpudec low-latency=true frame-plus=1 framedrop=false ! mfw_v4lsink sync=false async=false

Then start the client pipeline (board with analog video camera connected)

root@ventana:~# gst-launch tvsrc device=/dev/video0 ! vpuenc codec=avc ! udpsink host= port=9001 sync=false async=false

For more information, please view our GStreamer Software Wiki here: