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MX6Q VPU gstreamer-imx and intra refresh

Question asked by Pawel Cern on Nov 25, 2015
Latest reply on Sep 6, 2017 by Bob Smith

Hi,

 

I have to set up low latency H.264 video stream through low throughput data link. Video comes from PAL camera. Data link throughput is around 5Mbps. In classical approach, I-frames are problematic. They are pretty bandwidth consuming and transition from one end to other takes unacceptable period of time. I read about "intra refresh" technology, i. e. redistributing I-frame information across multiple P-frames. And started testing this approach on i.MX6Q with analog camera connected through ADV7180. Encoder gstreamer pipeline looks as follows:

 

gst-launch-1.0 imxv4l2videosrc device=/dev/video0 ! imxvpuenc_h264 bitrate=4000 gop-size=0 intra-refresh=90 ! rtph264pay pt=96 ! udpsink host=<....> port=6000

 

As you can see, I-frame generation is disabled (only one is produced at the beginning), as gop-size is set to 0. Intra-refresh is set to 90. All the screen in PAL resolution consists of 1620 macroblocks, so intra refresh period should take at most 18 frames.

 

When there is no data loss on the link, the picture looks fine. But when frame drop occurs, there are artifacts on the screen, going slowly right/down. The distortion is visible ~ 10 - 20 seconds. It seems intra refresh just doesn't work in this scenario.

 

For a comparison, I established similar pipeline on PC, with software x264 encoder plugin:

 

gst-launch-1.0 v4l2src device=/dev/video0 ! x264enc intra-refresh=true bitrate=1000 ! rtph264pay pt=96 ! udpsink host=<....> port=6000

 

And it looks better. Intra refresh process is clearly visible - vertical stripes of the image are processed step by step and finally the picture is OK.

 

I am pretty sure I did something wrong with encoder parameters. Could you please provide working example, which does H.264 encoding with intra-refresh and without I-frames? It may be without gstreamer plugin, may be just with imxvpuapi.

 

Kind regards

 

Pawel

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