Looking for some help to avoid delays on streaming

[sancat]

Hi,

I am a student at MIT, and we are trying to use Videolan VLC to stream live educational content to an audience of 40 to 150 people. At the moment we do have some problems with the delay between the “live” event and the actual transmission, and the amount of time it takes Windows Media to buffer the stream.

Here is the scenario.
We have a WinXP machine with a webcam connected. Through experimentation and forum reading, we arrived to a configuration that works:

Video capture through DirectShow from a Creative WebCam Pro (not using VFW)

dshow:// :dshow-vdev="Creative WebCam Pro" :dshow-adev="" :dshow-size="" :no-dshow-config

HTTP to my local IP address, on port 8080 (18.72.xx.xx). (xx.xx are actual numbers that do change because it is a dynamical IP). We do use a dynDNS pointer to solve this.

Encapsulation ASF,
Transcoding Video WM1 or WM2
Bit rate – This is the tricky part * See Below
No audio (I will deal with that later)
I also ask for a local copy on my screen.

:sout=#transcode{vcodec=WMV1,vb=256,scale=1}:duplicate{dst=display,dst=std{access=http,mux=asf,url=18.172.xx.xx:8080}}

To test if this works, I start a Windows Media with this URL, in my own machine or any other machine in the LAN, again using a dynDNS pointer, pointing to my IP 18.72.xx.xx
mms://mydynDNS.dynorg.cx:8080

Bit rate:
When the bit rate is high (around 512K/sec) the process goes smooth. VLC starts fairly quick to stream, and when Windows Media is started, it takes 3-5 secs to buffer, and starts. Delay is around that.

When the bit rate is reduced (64K/sec) the image on VLC screen gets little squares (as it is expected) and still comes up quick. However, when starting Windows Media, it takes forever to load, and buffer. When finally starts it has a delay of 4 mins sometimes (about the time it took to buffer). Reducing the buffer size settings on WM is not helpful; a one sec setting is not obeyed.

When the bit rate goes down to 32K it does not start at all.

Therefore, my question is whether this is a WM problem, or is there something that can be done to increase the immediacy on the VLC side. The best would be to have videoconference immediacy.

The second question is whether HTTP is the best way to avoid delays. We do not want people using special players or plugins to play stuff. WM, Winamp or Quicktime should do the work.

The third question is if this combination ASF-WM1 or 2 is the most efficient way to convey image streams with low bandwidth, without going for exotic new standards

And fourth, whether there is any additional experience with Peercast and Videolan, to help with bandwidth constraints.

Thanks for all your help!

Sandro
MIT-SDM

[markfm]

As far as I can tell, WMP really is bad news from a latency standpoint. I work with real-time video surveillance, things where operators are doing manual remote control sometimes, so latency is a no-no. My "gold standard" is to get latency down to the 200 ms range.

I've had pretty good luck using VLC for both the Server and Client, using UDP. I've gone in and cut all of the caches. I'm using VLC's MPEG4 default CODECs, but then again I do have a full T1 WAN to play with, can allocate 1 Mbps for the video. VLC's UDP multicast seems to work quite nicely, if you're working on a closed network, don't have to tunnel across the 'Net.

Right now it looks like I've got about 600 ms latency, and I fully expect to knock that down a few notches later this week, when I experiment with new builds of VLC -- the developers have been doing some work on speed recently, and I need sit-down time with our demo system to just work a table of cache-values-vs-latency.

Since VLC is cross-platform, and free, I would recommend that you avoid WMP. If you really want to stay with MS software, perhaps you could try Netmeeting, though you may run into resolution issues (my work requires 640x480)

Good luck!

[Guest]

Wmp delay can be set smaller from options/buffering. I use 1 sec for buffering; 512 for video DIV3 and 128 for audio mp3.

No probs with wmp9 here.


hodgin

[Prutser]

Wmp delay can be set smaller from options/buffering. I use 1 sec for buffering; 512 for video DIV3 and 128 for audio mp3.

No probs with wmp9 here.


hodgin

So did we, but once the stream's bitrate drops below a certain critical level, WMP appears to ignore all user settings and just buffer for ages. Have you tried it with really low quality streams? Like 384kbit or less?

regards,
Erik

[DF]

I thought you couldn't even stream TV through windows. I thought it had to be Linux only.

Am I wrong?
[/list]

[urbansond]

Look for the buffer setting in wm9. That may help to chop a little off, but udp straight to a vlc player is usually the better combination.