Re: [Discuss-gnuradio] Help with video link

[Alexander Buckley]

Hello Alexandru

thank you for your reply.

At the moment I am using a loopback cable on the USRP. I have been using MPEG_TS as well but i noticed after reading your comment I was missing the mpegtsdemux on my receiver chain.

I have something extremely crude operating now, though it is mostly a grey screen, the image isn't there yet. This is what I have set up so far:

transmit chain:

gst-launch v4l2src device=/dev/video0 ! 'video/x-raw-yuv,width=160,height=120' !  x264enc bitrate=1024 quantizer=10 tune=zerolatency ! mpegtsmux ! filesink location=txPIPE.ts

receiver:

gst-launch filesrc location=rxPIPE.ts ! mpegtsdemux ! queue  ! h264parse ! ffdec_h264 ! xvimagesink sync=false

and my GRC flow graph in between is:

TX:

File Source:

repeat: no

OFDM Mod

FFT len: 512

Occ tones: 200

prefix: 20

pad for USRP: yes

Payload length: 0

USRP Sink:

samp rate: 500K

RX:

USRP Source:

samp rate: 500K

OFDM deMod

FFT len: 512

Occ tones: 200

prefix: 20

pad for USRP: yes

Payload length: 0

SNR: 20

File Sink:

Unbuffered: off

Append: Overwrite

I have had trouble with a few things. What i notice when using an FFT Plot is that the signal is pulsating. I have been playing with CW values and gains on the USRP to see if that helps. It does somewhat but not totally. I wonder if this is a buffering issue. Though I have no feed back from my terminal, no underflow or overflow or TIMEOUT, both grstreamers are reporting to be playing (the rare time I get it through PREROLL into PLAYING on rx side)

I have been trying all sorts of FFT sizes, occupied tones, grstreamer bitrate values to no avail. All I have been able to do there is just make it worse.

I have the communication channel equations set up in excel so can input trial values and determine what my data rate through my flow graph should be, and then line that number up with gstreamer's bitrate. No luck there..

I had also considered using an error coding block (the CCSDS) but I read in the notes that comes with it the it wont work with packtised data. Which I am assuming then doesn't work with the MPEG-TS?

I have bypassed the USRP with a throttle block and the signal is better. It's more of the really low quality 'man in the space station' style. As it is not that good, I figure some of my flow graph numbers are off or I've missed something in my gstreamer command string.

Or my OFDM block is not set up right. I'm not sure what payload length should besides default value or what pad for USRP does.

Alex

On Wed, Mar 26, 2014 at 7:36 PM, Alexandru Csete <address@hidden> wrote:

Hi Alexander,

The de-facto standard way for sending video over the air (assuming you
can't use wifi-like links) is to encapsulate all video and audio into
a single, constant bitrate MPEG transport stream (aka. MPEG-TS). It's
a packetized format designed specifically for transmission over lossy
channels. MPEG-TS is used for DVB-T, DVB-S and probably also ATSC.

If you just want something quick & dirty you can try:
http://www.irrational.net/2014/03/02/digital-atv/

Alex

On Wed, Mar 26, 2014 at 5:42 PM, Alexander Buckley <address@hidden> wrote:
> Hello all,
>
> I am completely stumped with trying to stream video using gnu radio (GRC)
> and the USRP. I have been at it for an absurdly long time without success. I
> could really use some help. (With Unbuntu and the latest UHD/GNU radio)
>
> There has got to be someone who has done this, but so far google is not my
> friend.
>
> I have read so many sites of people looking for help and being given 'help'
> that doesn't work, the internet is now fully spammed when it comes to this
> subject.
>
> After days and days I read things like:
>  'To correctly and completely use the RTP payloaders on the sender and the
> receiver you need to write an application. It is not possible to write a
> full blown RTP server with a single gst-launch-1.0 line.'
> or that player 'x' isn't really player 'x' its a fork due to developers
> fighting and is rather broken..
>
> Most of what I read is about streaming over a network with a constant frame
> rate (adaptive bit rate) which really does not relate well to USRP?
>
>
> I have tried countless permutations of command line strings with various
> options using gstreamer, ffmpeg, vlc. mplayer
> I have tried UDP and File sink/source.
>
> I once I had it nearly working but could not get the player to stream with a
> constant bitrate (which i think usrp would require?). I have lost track of
> which player that was though.
>
>
> At this point I am completely desperate for a a solution. I am looking for
> any solution that works (even badly).
> All I am to do is put together a demo, and it is becoming clear I have no
> idea what I am doing. Either that or this as far far less trivial than one
> would think.
>
> I would greatly appreciate some help here as this endeavour is now becoming
> quite expensive.
>
>
> regards
> Alexander Buckley
>
>

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--
Alexander Buckley