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[Discuss-gnuradio] Piped Video Streaming Crash

From: Alexander Buckley
Subject: [Discuss-gnuradio] Piped Video Streaming Crash
Date: Fri, 21 Feb 2014 14:41:51 +0000

Hello all

Sorry if this is a duplicate, haven't found a thread with me specific config (no UDP).

ubuntu 12.10
GNU Radio
UHD 003.006.002-1

I have been trying to set up a video link (loop back cable) using named pipes but am stuck with a crash.
It works until I introduce the USRP into the loop. Though it is the same set up I use to transmit I text file without trouble.

What I have done:

VLC - Named Pipe - VLC    
(fail) - found reference to VLC bugs in forums so gave up on that

VLC - Named Pipe - Mplayer 

VLC - Named Pipe 1 - File Source GRC - File Sink GRC - Named Pipe 2 - Mplayer 

VLC - Named Pipe 1 - File Source GRC - OFDM MOD - OFDM DEMOD - File Sink GRC - Named Pipe 2 - Mplayer 

Now with hardware:
VLC - Named Pipe 1 - File Source GRC - OFDM MOD - USRP Sink- USRP -Source - OFDM DEMOD - File Sink GRC - Named Pipe 2 - Mplayer 
(FAILS!!). Reports: Segfault (core dumped).  GRC file is running, VLC is streaming. Fail occurs as soon as I open Named Pipe 2 with Mplayer

However, this is the identical GRC - USRP setup I use to repeatedly transmit a text file successfully.
I have no reason to believe the UHDlib is failing, the segfault I think is a python crash?

The parameters I am using:

cvlc v4l2:///dev/video0 :v4l2-width=160 :v4l2-height=120 :v4l2-aspect-ratio=4/3 --noaudio --sout="#transcode{vcodec=h264,vb=1024}:file{dst=./txPIPE.ts}" :sout-keep

sample rate 12.5M

GRC: - not sure of the impact of these settings
These are the ones I am not so sure of:
File source, repeat yes or no?
File Sink, unbuffered on or off? append file on or off?

I am guessing my problem is related to sample rate, buffer sizes, frame rate etc. I have tried a few permutations without luck though, but not everything.
I have not set camera fps -> v4l2-fps <float>
I have hoped the data flow back pressure would be dealt with by perhaps VLC with default setting (zero)? Or I'd just miss frames on reception?

Just looking for some suggestions here I as I have put a good bit of time into this now without luck.... 

Alexander Buckley

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