Re: [Discuss-gnuradio] Piped Video Streaming Crash

[Marcus Müller]

Hi Alexander,

interesting approach!
Just a few quick questions to understand better:

> 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

What is segfaulting? Mplayer or your Flowgraph?
If it's Mplayer I don't know, but it sounds like a solid Mplayer bug...

Also: Be aware that a named pipe might still have unread information from runs before; I guess the safest way would be rm'ing and mkfifo'ing right before every start.

> 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?
don't repeat. Wouldn't work anyway. a byte that came out of a named pipe is gone forever :)

> File Sink, unbuffered on or off? append file on or off?
buffering shouldn't change much, but since your fifo is basically a buffer, just use unbuffered.
Appending on/off is meaningless for named pipe file descriptors. use the off variant - it's how fifo's were meant to be used.

Do things work out if you replace Named Pipe 2 with an actual file and try to play back that afterwards?

Greetings
Marcus

On 02/21/2014 03:41 PM, Alexander Buckley wrote:

Hello all

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

System:

ubuntu 12.10

N2100

SBX

GNU Radio 3.7.2.1

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 

(works)

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

(works)

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

(works)

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:

VLC:

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

USRP: 

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.... 

regards

Alexander Buckley

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