Talk:Simple DVB with Gstreamer and GNU Radio
Revision as of 21:04, 4 September 2010 by Alex
- Building on the success of transferring data between GNU Radio and multimon using a named pipe, I decided to try the same trick to send real time video from Gstreamer to GNU Radio. It worked!
- Implemented a simple video transmission simulator by sending the video through a GMSK modulator, adding noise, then GMSK demodulator. See recorded video.
- Although the MPEG-TS muxer available in Gstreamer can not deliver CBR, sending the GMSK modulated video to the USRP didn't seem to be a problem.
- Having only one USRP I didn't try to receive and decode the video.
- Successful on the air tests of the DVB setup using a videotestsrc
- Location: OZ7SAT
- Repeated on the air tests at OZ7SAT (to be sure that it wasn't just some sort of random luck)
- Video test source: http://www.youtube.com/watch?v=2VUZ7H60F68
- Logitech Webcam Pro 9000: http://www.youtube.com/watch?v=RzIe_IWGvmA
- At Høm for the weekend and only brought one USRP and one laptop
- Created a full duplex transceiver version of the GMSK TX+RX so that I could run both transmitter and receiver using only one USRP and computer: http://www.youtube.com/watch?v=dJg2zAd3kRY
- The transceiver was running stable for more than 4.5 hours, see last screenshot.
- With this setup, the video appeared to be more choppy than with the two-computer setup.
- Imported the source code to http://github.com/csete/gnuradio-dvb
- GMSK modulator generates 2 samples/symbol and I have 1 bit/symbol. Therefore, the input data rate to the GMSK modulator should be 500 kbps for a 1 Msps stream to the USRP.
- The packet encoder adds 12 bytes overhead to each packet – at least when using default access code. With a payload size of 4000, this overhead corresponds to 1.5 kbps.
- Setting H-264 encoder bitrate to 498 kbps (didn't make much difference).
- Tested Theora in Ogg container using videotestsrc and the simulator. Worked very well.
- Tested the Theora version using the gmsk_trx script. Worked well and very stable for 2+ hours using the videotestsrc.
- With camera it looses sync after a few minutes and mplayer spits out "Ogg: bad packet in stream 0" messages.