Re: [Discuss-gnuradio] Realtime streaming issues using gr-dvt on E312

[Ron Economos]

Kailash,

    The DVB-T receiver is very compute intensive. Even on a 4 core X86 processor, it may be difficult to run the example flow graph with the default parameters. To make matters worse, the SSE2 optimizations in the Viterbi decoder are not available on ARM.

    For smooth playback, you have to match the Transport Stream bit-rate to the sample rate. Here's a program to calculate the TS rate from the sample rate.

http://www.w6rz.net/dvbtrate.c

For the 310k sample rate you're using, the bit-rates would be:

QPSK             1/4      1/8     1/16     1/32
coderate = 1/2 168733.5 187481.6 198509.9 204525.4
coderate = 2/3 224977.9 249975.5 264679.9 272700.5
coderate = 3/4 253100.2 281222.4 297764.9 306788.1
coderate = 5/6 281222.4 312469.4 330849.9 340875.7
coderate = 7/8 295283.5 328092.8 347392.4 357919.5
QAM-16
coderate = 1/2 337466.9 374963.2 397019.9 409050.8
coderate = 2/3 449955.9 499951.0 529359.9 545401.1
coderate = 3/4 506200.4 562444.9 595529.8 613576.2
coderate = 5/6 562444.9 624938.7 661699.8 681751.3
coderate = 7/8 590567.1 656185.7 694784.8 715838.9
QAM-64
coderate = 1/2 506200.4 562444.9 595529.8 613576.2
coderate = 2/3 674933.8 749926.5 794039.8 818101.6
coderate = 3/4 759300.6 843667.3 893294.8 920364.3
coderate = 5/6 843667.3 937408.1 992549.7 1022627.0
coderate = 7/8 885850.6 984278.5 1042177.2 1073758.4

The combined video and audio bit-rates have to be less than the TS rate.

Also, when you change the guard interval, you have to change the CP length on the OFDM Cyclic Prefixer. 1/32 = 256, 1/16 = 512, 1/8 = 1024 and 1/4 = 2048.

Ron

On 02/19/2018 10:00 PM, kailash kumar wrote:

Hi,

I am using DVT module for realtime streaming of mpeg ts file.
MPEG -> DVT -> USRP <----> USRP -> DVT -> UDP Sink -> VLC

I am having following issues wrt performance:

1. Audio is not not synced with respect to video frame causing stutter or video getting stuck on VLC.
2. At times video gets stuck and unable to recover on VLC.

Here is what I have tried so far:

1. Stripping down video to 240x144 at 10 fps or less to cut down on bandwidth requirements
2. Varying audio bit-rates from 32 to 384 Kbps.
3. Trying out different combination of sample rates and tx/rx frequency.
4. Varying code rate and guard interval
5. Trying out different combination of modulation techniques (QAM/QPSK).

I am attaching tx and rx grc files for reference.
Please let me know if something is missing from the flowgraph to achieve decent real-time streaming from one E312 USRP to another.

Thanks

Kailash

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