MultiScreener 0.95
February 3, 2009, Zach Poff
Always Check for updates: http://www.zachpoff.com
Summary:
MultiScreener is a set of freeware applications that synchronize the playback of Quicktime movies on multiple computers, using a local network to tie them all together. (It can also synchronize multiple movies on the same computer using multiple monitors.)
It is intended for multi-channel video art, video walls, etc. I designed it as an artist-friendly low-budget alternative to the expensive combo of industrial DVD players (Pioneer DVD-V7400, DVD-V5000) and Dave Jones Design sync boxes. Those systems are fantastic, but if you have a few computers and a network hub, MultiScreener is worth a try.
There are two applications: Server and Client. The server plays a movie and also sends position information over the network. Each client compares its position to the server's and changes its playback speed to compensate.
MultiScreener was originally based on the implication that each client would run on its own machine, but you can run multiple clients on the same computer, with each client feeding a different monitor. (See Server and Multiple Clients... section.)
Looping and de-interlacing are available, and all settings are automatically saved for unattended startup. MultiScreener can output to the computer screen in fullscreen mode, or to external video devices like DV decks. There is no native resolution or frame-rate, so all Quicktime video formats are supported equally.
How it Works:
The server broadcasts its messages via multicast, so no knowledge of server/client IP addresses are required. Normally, the client will adjust its playback rate by tiny increments, smoothed over time to avoid audible pitch changes. If the server suddenly jumps to an unexpected frame (like when a loop occurs), the client changes sync strategies, immediately jumping to the server's frame and lighting up the "Finding Frame" indicator. Afterwards MultiScreener resumes the normal syncing method. If the Server pauses on a frame, the client will "hover" around that frame waiting to continue. If the server disappears, or the network breaks, the client will keep playing for a moment and then pause. When the server reappears, the client will resync to it immediately. (So clients and the server can be launched in any order, added and removed at will. It will just work.)
Client Offset and decoder delays:
In rare cases the sync meter can be inaccurate if Quicktime takes significant time to decompress the frames of the movie. In this case, MultiScreener delivers each frame to the decoder but the whole Quicktime architecture seems to be lagging a bit. There is no way for MultiScreener to be made aware of the this delay, so there is a "Client Offset" adjustment instead. Usually it should be set to zero.
While viewing in fullscreen mode, use the left and right arrow keys to adjust the offset in 1/4-frame increments. (Positive numbers make the client early, negative makes it late.)
Fullscreen and External Video:
Typically, MultiScreener users play their movies fullscreen, so any data projector or computer monitor can be used for presentation. All frame-rates and dimensions are supported (including NTSC, PAL, HD formats) with no unnecessary scaling, up to the limits of your hardware and Quicktime capabilities. The graphics card does the scaling directly from the movie to the screen via openGL. (The software has no "native" format, although the small video preview window is locked at 320 x 240.) Since computer displays are inherently progressive-scan devices, MultiScreener can de-interlace your movie too (see the Movie Preparation for more info.)
For some movies, MultiScreener can send the video directly to special hardware for better decompression. The most common example is DV over Firewire. If you attach a DV camera, deck, or converter box to your Firewire port, MultiScreener will let you choose it as an output instead of the computer screen. This provides the best quality and lowest CPU load for DV footage. Note: DV devices introduce a noticeable video delay (about 4 frames), so you shouldn't mix DV decks and Computer Screens in the same project. Your movie must be encoded in the format that your external hardware expects. (MultiScreener won't display a 320x240 MP4 file on your DV deck!) DV is the most popular example of this technique, but any Quicktime-compatible external hardware should work. (DVCProHD, etc)
HD Performance:
I have tested MultiScreener with many types of media. These are my recommendations:
Dimensions Codecs Minimum Hardware
480i or 480p SD DV-NTSC/DV-PAL G4 Mac Mini, G4 tower (1 GHz or above)
720p HD Photo-JPEG (medium) Dual G5, Intel Mac Mini (Dual 1.66 or above)
1080i or 1080p HD Photo-JPEG (medium) Mac Pro (maybe a Quad G5 would do it?)
Note that MultiScreener was made with a cross-platform graphical programming language, not native Mac OS code. HD performance is dissapointing. Quicktime player might play your 1080p files perfectly on an Intel Mini, but MultiScreener requires much more horsepower. This seriously limits its usefulness, but there is nothing I can do except wait for MAX/MSP to get more efficient in the future.
If you are having trouble getting adequate HD performance, try slowing the server's "transmit_interval" to 500ms (see Preferences below). That might give the clients some breathing room. Also experiment with the "overdrive" preference.
Make sure you are aware of the movie codec because it's crucial for HD playback (see Movie Preparation below).
Movie Preparation:
Movies should be prepped to match your output device (computer screen, DV over firewire), because MultiScreener will scale the image to fit the screen. That means that widescreen movies will look wrong on 4:3 monitors, and 4:3 movies will look wrong on widescreen monitors. Try setting your monitor resolution to a ratio that matches your movie instead of your display. For example: You can play 4:3 movies on a widescreen iMac or laptop by choosing a 4:3 display resolution that is not "stretched". The computer will insert black "pillar box" bars on the sides of the screen, and you won't need to change the dimensions your original movie.
Your server and client movies should be compressed in the same format. (DV NTSC and PAL seem to work fine for me, but experiment to find what works best for you.) All of the math is based on the Quicktime "timescale" of the movies. The timescale defines how many subdivisions of each second are stored in the movie file. It is not the frame-rate. A DV NTSC movie from Final Cut Pro will have a timescale of 2997 but Quicktime Pro will export the same type of movie with a timescale of 600. It is crucial that you have matching timescales on your movies to ensure that the server and client speak the same language. (MultiScreener displays the timescale of the current movie, so you can easily check.)
MultiScreener can de-interlace your movie, but it uses the Quicktime scaler which isn't as good as some advanced de-interlacers. (It's at least as good as the standard Final Cut Pro de-interlace filter, though.) If your movie came from an interlaced source and you want the best quality on a progressive display then you might want to de-interlace in advance.
You should consider the compression "codec" when exporting your movie for MultiScreener. Most modern codecs (like H264, MPEG4, MPEG2) use temporal compression, so only certain frames are recorded in their entirety. Do not use temporal compression for MultiScreener. Those codecs require more processor power and they introduce decompression delays which make sync unreliable. Restrict yourself to spatial compression instead (like DV, Photo-JPEG, Apple Intermediate, ProRes). These formats require more disk space (and disk performance) but MultiScreener can keep them in sync.
(If you throw all caution to the wind and use H264, at least uncheck "frame reordering" in the compression settings during export. Frame-reordering will cause trippy forwards-backwards stuttering whenever MultiScreener tries to update the speed!)
Preferences:
All settings are saved automatically to an xml preferences file, as soon as you make the change (so if the computer crashes, your settings will not be lost). When the application starts, it automatically loads your movie, recalls your settings, and (optionally) goes into fullscreen mode. Great for unattended exhibitions. You can edit the xml with any text editor. MultiScreener will read the file on the next launch (but don't mess with the xml while MultiScreener is running).
Hidden Preferences:
(not exposed in the main user-interface)
"overdrive" options: 0, 1 [default 1] -- Sets the MAX/MSP scheduler to operate in "overdrive" mode. In this mode, internal timing is less susceptible to interference from drawing the screen, moving the mouse, etc. But it may have a negative effect on stability in some cases.
"interrupt" options: 0, 1 [default 0] -- (Requires overdrive: 1) Sets the MAX/MSP scheduler to operate at audio interrupt - may help solidify timing on slow computers, may not.
"transmit_interval(ms)" options: number of milliseconds [default 100] -- How often the server sends its position over the network. The default works fine but slower values might be better for slower computers/networks
"window_coords_x" pixels -- The horizontal position of the top-left corner of the window (multiple monitors may have negative numbers)
"window_coords_y" pixels -- The vertical position of the top-left corner of the window (multiple monitors may have negative numbers)
"frame_offset" (client only) -- This isn't hidden, it's in the user-interface. But you should know that frame_offset values are stored in Quicktime time-units, not the 1/4-frame increments reported onscreen.
Server and Client on the same computer:
Multiscreener was originally designed with the implication that each Server or Client application would run on its own computer. There was interest in multiple monitor support, so now you can run two channels of video on the same computer. The apps recognize which monitor they were occupying before you triggered fullscreen, and they go to fullscreen on that monitor only. (This should work with a single dual-head graphics card, or multiple single-head cards, or a laptop.) The window position is saved and restored through the preferences, so the apps will remember which monitor to occupy when relaunched. When the first app enters fullscreen mode, you can elect to keep the mouse visible by un-checking "Hide Mouse in F-S". That way you can launch the other apps. I also provide an Applescript to automate the process:
To launch the Client and Server using multiple monitors:
1) Be sure the applications are in your Applications folder. (Yes, it matters)
2) Open each app individually and do the following:
a) Choose the movie and define your options. Be sure to select AUTO FULL SCREEN.
b) Drag the app to whichever monitor you want it to occupy.
c) Close it.
3) Locate the MultiScreener Launcher (Dual Head).app Applescript
(This programmatically opens the 2 apps, one after the other.)
4) Run the Applescript (or put it into your "Login Items" in "System Preferences... / Accounts" so it runs whenever the computer starts.)
To quit when using multiple monitors:
1) Quit one app with Command-Q
2) Switch apps using Command-Tab
3) Quit the other app with Command-Q
Server and Multiple Clients on the same computer:
I have discovered a technique to run a Server and multiple Clients simultaneously, with each app feeding a different monitor. It involves copying and renaming the clients, then triggering them to run via Applescript so they can all live happily in fullscreen mode on separate monitors. There are much more elegant ways of doing multi-channel video playback on a single computer, but MultiScreener "accidentally" works in this context. (You will need a pretty fast computer to handle all of that video, though!)
To prepare a new Client:
1) Inside your MultiScreener folder, make a new folder with a name like "MultiScreener Client 2 folder"
2) Copy the Client application and its preferences into the new folder. (Select them and drag them while holding the option key.)
3) Rename the copy to "MultiScreener Client 2"
4) Right-click on the copy and choose "Show Package Contents".
5) Inside the "Contents" folder you will find "MultiScreener Client.mxf" Rename it to "MultiScreener Client 2.mxf"
Repeat these steps to prepare as many clients as you need.
To use them:
1) Basically just follow the Server and One Client instructions, but modify the Applescript to reflect your new clients. (So, tell Server to activate, then "MultiScreener Client", then "MultiScreener Client 2" etc...)
Fullscreen and "Tearing"
Some graphics cards exhibit a phenomenon known as "tearing", where horizontal strips of the previous frame will appear on the display. This is caused by the graphics-card buffers being improperly synced to the vertical refresh rate of the monitor. MultiScreener tries to alleviate this by enabling "VBL sync" on the graphics card, but some cards can't manage to do it. This problem is more likely when using multiple monitors.
If you experience "tearing", make sure your system software (and therefore your graphics drivers) are up to date. Also, try adjusting the refresh-rate of your monitor in "System Preferences... / Displays". Some codecs tend to tear more than others.
Applescripts:
There are several Applescripts included to help launch the MultiScreener apps in unattended installations. Typically I would just add the app to the "Login Items" in "System Preferences... / Accounts" but on slower machines, startup apps won't launch properly because they get triggered before the computer is finished starting. Before using these scripts, be sure the MultiScreener applications are in your Applications folder.
MultiScreener Launcher (Server).app
MultiScreener Launcher (Client).app
Drop one of these into your "Login Items" instead of the app itself. These scripts wait 10 seconds before launching their accompanying Multiscreener app. That should be enough time to ensure success.
MultiScreener Launcher (Dual Head).app
This script is similar to the others, but it launches the Server and Client on the same machine. (See Server and Client... above.)
GPL License:
MultiScreener is Copyright 2008, 2009 by Zach Poff. It is Free Software, released under a GPL 3.0 license. You are free to copy it, modify it, and redistribute your changes provided that all derivative products remain GPL licensed. The source files are included in the download. (See http://www.gnu.org/licenses/gpl-faq.html for details about this license.)
There is a caveat: MultiScreener was developed in the (non-free) MAX5 visual programming environment ( http://www.cycling74.com ) which is required if you want to edit the source code. The MultiScreener application contains the MAX5 "Runtime" environment, which is not GPL, so my license pertains to my contributions only.
(Former versions were distributed under a Creative Commons by-nc-sa license, which was a little too vague and restrictive with respect to commercial use of the software. The GPL provides more freedom to use the software commercially.)
Change Log:
Version 0.95 (Feb 03, 2009)
Changed to GPL 3.0 license
Recompiled with MAX5
Tested HD playback
Fixed: Fixed error in client timing comparison. (improved sync accuracy).
Fixed: Fixed occasional loss or overwrite of xml preferences file
Fixed: client sync meter was sometimes inaccurate
Fixed: Simplified and optimized speed-control math
Fixed: Simplified window-position save/recall at startup
Fixed: Counters sometimes displayed wrong times
Fixed: Now uses more conservative timing when entering/exiting fullscreen
Fixed: Changed size of filename display to accommodate long filenames
Fixed: changed "Way Off!" indicator into "Finding Frame" indicator
Added: "Mute Sound" button added
Added: "Hide Mouse in Full-Screen" button added
Added: Client now indicates playback speed
Added: Client now has user-settable frame offset
Version 0.93b (May 23, 2008)
Added: Updated the README file to reveal a way to run multiple clients on the same computer.
(There are no code changes!)
Version 0.93 (May 20, 2008)
Added: Now supports multiple monitors (2 fullscreen movies on one machine)
Added: Apps now remember their monitor position
Added: Expanded README file with lots of new info
Added: Applescripts are now included for unattended launching and multiple monitors
Added: Movie timescale data is now displayed
Fixed: Changed fullscreen startup delay to 5 seconds to help with slower machines
Fixed: Settings are now saved immediately, not when app closes
Version 0.92 (May 09, 2008)
Fixed: reduced CPU load on client and server by limiting GUI updates and slowing down non-critical math
Fixed: The window in which normal tracking operates is now (+/-) 1/4 second, regardless of movie frame-rate or Quicktime time-units/second. If the sync falls outside this window then we switch to emergency mode and jump directly to the server's frame (triggering the new "Way Off!" indicator on the way).
Added: de-interlacing (uses same method as Quicktime player - nothing fancy).
Added: "Way Off!" indicator to indicate when the client switches from normal to emergency sync mode
Added: numerous advanced options are now acessible via XML prefs
Added: software license (Creative Commons Attribution-Noncommercial-Share Alike)
Versions 0.8 - 0.91 (May, 2008)
Internal test versions
Version 0.7b (April 9, 2008)
Fixed: problem with client not entering fullscreen.
Version 0.7 (April 8, 2008)
First release