Streaming video - do we all see the same?

Answer - No.

I ran 2 avis from my computer side by side on the screen.

As I expected, they both saw no video as they walked up to screen. As each clicked, his video, and only his, started.

They then ran together, but 3 minutes apart.

What I did NOT expect - when one clicked pause - both paused.

When one clicked restart, both restarted, and ran synchronised.

Now I ask - is this because the one computer is running bothe streams, and is linking the commands, or is LL deliberately sending some synchronising commands?

Need a fellow tester

How do you run two avies from one computer? Separate installations?

The video will be synced if it is live.

If it is static, it will not be synced for different viewers. We will try to add scriptable seek controls and auto-seeking to make the default behavior synced.

From what I understand, the video isn't played if the local user hasn't attempted to play a video of their own will. (i.e., the actual video component isn't loaded until the user wants to play a video.)
This is nice... would be nicer if the video would "catch up" (if applicable), too, but that's, in my opinion, secondary.

You can run two avs from one machine in windows by adding the -multiple switch to the target field in the shortcut used to start Second Life.

Example:


Just name each shortcut with the av's name and it is nice and simple. They work fine when you want to just run one av.

^ Thanks Suez, I didn't know about that one before -- the additional level of providing usernames and passwords I mean. Should be handy.

You're welcome, Torley.

If you use -logon and there's a dialog for downloading a new client the client will not pop it up and attempt to log on anyway. Repeatedly.

To say LL will add sync'd movies, is simply not possible. Given that the media is streamed from one source and is multicast, your distance from that source and your connection quality will always be the deciding factor.

One way of partially syncing media is to use a channel broadcaster that repeats/loops the media at given times, effectively using key frames. However there will always be differences when you also consider some viewers set Imediate start, and some Slow start depending on the buffer/cache size selected in the QuickTime player/pluggin. Unicasting overcomes some of that latency, but that would require each user to join a peer to peer network. As LL do not provide, nor control the streaming of media into SL, it would require 3rd party intervention..... one you pay for.

If the media server has limited burst ram, cpu cycles, shared network connection and or bandwidth, then it becomes a first come first served situation, generally bringing the whole broadcast down to a crawl (lag). Our own media is streamed into SL via 5 servers across the USA and Europe, all interconnected via load balancer zone pointers, directing the viewer either to the nearest source, or the one with the greatest available resources. A Total of 10gb burst ram and 10.6tb bandwidth means that when you get delayed starting, or restarting of the movie whilst your buffer tries to cope with the stream data bit rate, then that is your end.

When you run media in SL, you are doing two things, sharing bandwidth with the client and the media, add voice and then you are sharing 3 ways. In addition, rendering media through the QT pluggin loaded into the client, adds rendering cycles to the client engine. Whilst some media appears to be of a low data bit rate, using codex like MP4 actually adds significantly to the decoding of the stream on the fly, to the Client/System.

You can check this out using a simplified version of the reports available in the client by pressing Ctrl+Shift+2. The main pipeline UpdateImage (lime green colour band) is associated to the work that the client is having to do when rendering media. Turn off the media and you will see that it is quite a small percentage, turn the media on, and that percentage grows significantly.

Our movies are rendered through templates developed to balance the data bit rate and the work/loading on the client. The aim is to acheive a 20-30% maximum loading on the rendering engine/decoding, with a data bit rate of 100kbps. The vast majority of media streamed into SL, either loads the client upto 80% (I have seen examples that load my system by over 90%, almost causing fps to drop to 1fps), or have such a high data bit rate that the movie fails to start, or continously restarts overloading the buffers.

Now we have sculpties.. this adds to the rendering of the client engine pipelines, they update at a frame rate of between 12.5-15fps. Unless you interlace your movies frame rate, equalising the rendering cycles, then the loading becomes additive. A 50% loading movie becomes 80% in the same vacinity of sculpties.

Squeebee's MST3K Theater is using a script for this:

If you enter the cinema and start a movie that's allready running you can click on a prim that runs a script which syncs your video with the others. if you know MST3K you'll know it's extremely important, that ppl all see the same scenes, so they can riff together.

Maybe they should market this script?

I suspect this is done using RSTP media. RSTP file headers contain a list of the keyframes of the media (like an index), standard progressive and or download and watch formats do not.

Holy delayed-response, SuezanneC!!

Well, the necro-post explains why I was surprised to see Linden-Orange postings.

yea wow phil linden

oh its from 2k5

and WOW what a hell of a delay

you know its hard to bitch about the lindens taking their sweet time when you do this kind of stuff (right?)

I can't say, only that the movies running in that place come as mp4-files.

And I am pretty sure it isn't just some keyframes like every 2 minutes or something, because the synch works every time you klick it and brings you to the right bit of film each time.

We're talking a cinema with sometimes >30 ppl in at some sessions, and I have never heard that someone doesn't get to the right position in the movie when synching.

But of course I too can be wrong. I suggest you have a look yourself if you're interested - the place is in my ingame Picks.

You will find most editing programme add keyframes at around the 25fps mark (thats generally 1 per second)
MP4 is not just a codec, it is also a wrapper format. If the file name ends in MP4 then it denotes the wrapper format. A wrapper can contain other attributes such as H.264 Hinted file codec in the header, this can be a standalone file or compressed within the media header. This tells the delivery system how to handle the file.

Ah, ok, so I learned a bit again. Thanks. And a keyframe each second or so would defenitely work for the way it's used there.

Most rendering editing programmes allow you to determine the keyframe frequency, the default is 25th frame. Much of the need for keyframes is to maintain sync between any music tracks and the moving media. For the most part, music takes presidence over the moving media as a few dropped frames will not be noticable as dropped music. It is also used for sync'ing the refresh rates for TV tuners.

It it also used since the intruduction of stereo etc, as it relies on splitting one main track which has both tracks combined, and a left track which is deducted from the main track to produce left and right tracks. This is sync'd by key frames.