IMX6 : Video streaming over serial port using Gstreamer and H264 encoder

[vk_gst]

Hello GStreamer Experts,

Recently, I have started to work on a project that aims at live video
streaming applications based on imx6 processors. A quick description of what
I have done so far and what I am trying to do:

1. Setup: imx6 board(Boundary devices Sabre Lite) acting as the video
server(using GStreamer imx plugins), and a PC running Ubuntu on it that
receives data from imx6 and streams the video using GStreamer features.
2. On the imx6 processor, I run the 'testvideosrc' and have successfully
streamed it using the RTP over UDP.
3. Since accessing the serial port is similar to writing and reading a file
in Linux, next I tried out dumping the video data from imx6 board to a
serial port and reading this serial port on the PC. For this, the baud rate
of both devices was configured to 115200 baud. The encoding 'bitrate' is
configured to 5Kbps. Here are the commands:

imx6: gst-launch-1.0 -v videotestsrc pattern=18 !
video/x-raw,width=100,height=50 ! imxvpuenc_h264 bitrate=5 ! h264parse !
filesink location=/dev/ttyUSB1 

PC: CAPS=video/x-h264
PC:  gst-launch-1.0 -v filesrc location=/dev/ttyUSB1 ! $CAPS ! h264parse !
avdec_h264 ! autovideosink sync=true

There are no errors observed on the imx6 board. 
However, I see the following errors at the PC side : 
PC:# GST_DEBUG=3 gst-launch-1.0 -v filesrc location=/dev/ttyUSB1 ! $CAPS !
h264parse ! avdec_h264 ! autovideosink sync=true
 Setting pipeline to PAUSED …
0:00:00.066439392 15475 0x556d8a01d160 WARN basesrc
gstbasesrc.c:3583:gst_base_src_start_complete: pad not activated yet
 Pipeline is PREROLLING …
0:00:21.730466251 15475 0x556d8a000940 WARN capsfilter
gstcapsfilter.c:455:gst_capsfilter_prepare_buf: error: Filter caps do not
completely specify the output format
 0:00:21.730523691 15475 0x556d8a000940 WARN capsfilter
gstcapsfilter.c:455:gst_capsfilter_prepare_buf: error: Output caps are
unfixed: video/x-h264, width=(int)[ 1, 8192 ], height=(int)[ 1, 8192 ],
framerate=(fraction)[ 0/1, 2147483647/1 ]
 0:00:21.730676173 15475 0x556d8a000940 WARN basetransform
gstbasetransform.c:2159:default_generate_output: could not get buffer from
pool: error
 0:00:21.730742223 15475 0x556d8a000940 WARN basesrc
gstbasesrc.c:3055:gst_base_src_loop: error: Internal data stream error.
 0:00:21.730775478 15475 0x556d8a000940 WARN basesrc
gstbasesrc.c:3055:gst_base_src_loop: error: streaming stopped, reason error
(-5)
 ERROR: from element /GstPipeline:pipeline0/GstCapsFilter:capsfilter0:
Filter caps do not completely specify the output format
 Additional debug info:
 gstcapsfilter.c(455): gst_capsfilter_prepare_buf ():
/GstPipeline:pipeline0/GstCapsFilter:capsfilter0:
 Output caps are unfixed: video/x-h264, width=(int)[ 1, 8192 ],
height=(int)[ 1, 8192 ], framerate=(fraction)[ 0/1, 2147483647/1 ]
 ERROR: pipeline doesn’t want to preroll.
 Setting pipeline to NULL …
Freeing pipeline …


4. Since, the encoding rate is 5Kbps (bitrate=5, as specified in the above
command), I suppose it is possible to send this amount of data via the
serial port. I realize that currently, the caps negotiation fails, however,
I am unsure of how to proceed with this. 

5. On the PC side, reading the serial port with 'cat /dev/ttyUSB1' succeeds
with limited data. The data is unreadable(as expected), however it is not a
continuous stream.

Does anyone have an idea, on how to solve this. 
My later test, would be to use an actual camera(MIPI) and try streaming it
over serial port. Does it seem feasible or is a completely crazy idea to do? 



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