This file is indexed.

/usr/share/psychtoolbox-3/PsychDemos/VideoPluginCaptureDemo.m is in psychtoolbox-3-common 3.0.11.20140816.dfsg1-1.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
function VideoPluginCaptureDemo(deviceIds, syncmode, movieName)
% Demonstrate simple use of built-in video capture engine.
%
% VideoMultiCameraCaptureDemo([deviceIds=all][, syncmode=0][, movieName])
%
% VideoMultiCameraCaptureDemo captures simultaneously from all cameras
% connected to your computer, or a subset of cameras if it is specified
% in the optional vector 'deviceIds', and then shows their video feeds
% in individual Psychtoolbox windows.
%
% The optional 'syncmode' flag allows to select synchronization strategy
% for multi-cam capture: 0 = None, all free-running. 4 = Software sync,
% 8 = Firewire Bus-Sync, 16 = Hardware (TTL) trigger sync.
%
% The optional 'movieName' string, if provided, will enable video recording
% of each cameras video into a dedicated movie file, which consists of the
% movieName and a unique camera number.
%
% By default, a capture rate of 30 frames per second at a resolution of
% 640 x 480 pixels is requested, and the timecode and interframe interval
% of each captured image is displayed in the top-left corner of each window.
% A press of the ESCape key ends the demo. The demo also ends automatically
% after a timeout of 10 minutes is reached.
%
% This demo has various hard-coded parameters which allow you to tinker with
% things like Bayer filtering on the camera, versus on the host cpu, versus
% offline later on during playback of recorded video, to select different
% tradeoffs between quality, cpu load, speed and bus bandwidth use. It also
% allows to play with high bit depth (> 8 bpc) color and luminance formats,
% lossless video recording and other bits and pieces. Change the variables
% as you see fit and read the source carefully.
%

% History:
% 04-Nov-2013	mk  Written.

if IsWin
    error('Sorry, this demo is not supported on MS-Windows, as it needs the DC1394 video capture engine.');
end

% Default init and setup:
PsychDefaultSetup(2);

escape = KbName('ESCAPE');
backKey = KbName('LeftArrow');
forwardKey = KbName('RightArrow');

if nargin < 1
    deviceIds=[];
end

if nargin < 2 || isempty(syncmode)
    syncmode = 8;
else
    if ~ismember(syncmode, [0,4,8,16])
        error('Invalid syncmode! Must be 0, 4, 8 or 16!');
    end
end

if nargin < 3 || isempty(movieName)
    doVideoRecording = 0;
else
    doVideoRecording = 1;
end

roi = [0 0 768 576];
depth = 3; % Choose a color depth of 1 if you want raw sensor data - or grayscale of course. 3 for RGB.
% Mode 4 would be the correct mode for raw sensor -> rgb bayer conversion on Basler cameras.
% Mode 3 would pass raw sensor data instead.
convMode = 4;
bayerPattern = 0; % This would be the correct bayer pattern for Basler color cameras.
debayerMethod = 3; % Debayer algorithm: 0 = Fastest, ..., 3 = High quality, 4-7 = May or may not work.

% Bitdepth to request from camera: 8 bpc is standard. 16 bpc requests anything between 9 bpc and 16 bpc:
bitdepth = 8;

% Set dropframes = 0 if multiple frames shall be recorded for sync timing checks, 1 otherwise:
dropframes = 1;

% Flags to use for video recording. 16 = Use multi-threaded recording.
if doVideoRecording
    captureFlags = 16;
    codec = ':CodecType=DEFAULTencoder UseVFR'; % Use default codec. UseVFR for variable framerate recording.
    
    % The huffyuv and ffenc_sgi codecs are lossless codecs. They use lossless compression, so video images
    % are stored exactly, but the resulting movie files will be comparably large!
    % These are mostly useful if you want to use the material for sensitive computer vision algorithms,
    % or if you want to store raw camera sensor data without Bayer filtering and perform the Bayer filtering
    % for raw sensor -> RGB conversion later on during playback. In that case you will need exact storage of
    % video and hence one of these codecs.
    %codec = ':CodecType=huffyuv UseVFR'; % Use HuffYUV Huffman encoded lossless codec. UseVFR for variable framerate recording.
    %codec = ':CodecType=ffenc_sgi UseVFR'; % Use SGI-RLE lossless codec. UseVFR for variable framerate recording.
    
    % For > 8 bpc recording, we need to use our own proprietary video encoding:
    % Note: Only use with lossless video codecs makes sense for 16 bpc mode.
    % Currently supported are huffyuv and ffenc_sgi.
    if bitdepth > 8
        codec = [codec ' UsePTB16BPC'];
    end
else
    captureFlags = 16;
    codec = [];
end

% Optional processing string for dropframes = 0 && captureFlags & 16 capture/recording:
processingString = '';

% Example processingString to apply an image warping effect:
%processingString = 'ffmpegcolorspace ! warptv ! ffmpegcolorspace ! capsfilter caps="video/x-raw-rgb, bpp=(int)24, depth=(int)24, endianess=(int)4321, red_mask=(int)16711680, green_mask=(int)65280, blue_mask=(int)255"';

% Set noMaster = 1 if all cams are externally hardware triggered slaves, 0 otherwise:
noMaster = 1;

% Always use a master, ie., noMaster false if not hardware synced.
if syncmode ~= 16
    noMaster = 0;
end

% We limit default framerate to 30 fps instead of auto-detected maximum
% as supported by a camera in order to limit the consumption of bus bandwidth.
% Otherwise we might run out of bandwidth with multiple connected cameras.
fps = 30;

% Select maximum number of frames to capture and record: Zero for "unlimited"
maxTargetFrameCount = 0;

% For now we only use the DC1394-Firewire capture engine, as setup with
% the GStreamer engine is not impossible, but more difficult/error-prone
% and less flexible when it comes to complex camera control and sync.
Screen('Preference', 'DefaultVideocaptureEngine', 1);

% Also disable sync tests, as visual timing doesn't work well anyway
% on windowed non-fullscreen GUI windows:
oldsynctests = Screen('Preference', 'SkipSyncTests', 2);

screenid=max(Screen('Screens'));

if isempty(deviceIds)
    devs = Screen('VideoCaptureDevices');
    for i=1:length(devs)
        % Use device if either its deviceIndex is not zero, or all enumerated devices if
        % the libdc1394 capture engine is in use. On other engines, deviceIndex 0 is special
        % in that it defines the default capture device. The same device shows up a second
        % time under a distinct device index, so we have to filter out deviceIndex 0 to avoid
        % opening the same camera twice:
        if (devs(i).DeviceIndex ~= 0) || (Screen('Preference', 'DefaultVideocaptureEngine') == 1)
            disp(devs(i));
            deviceIds = [deviceIds, devs(i).DeviceIndex]; %#ok<AGROW>
        end
    end
end

if isempty(deviceIds)
    fprintf('Sorry, could not detect any suitable video cameras. Bye.\n');
    return;
end

try
    for i=1:length(deviceIds)
        % Open oncreen window for i'th camera:
        win(i) = PsychImaging('OpenWindow', screenid, 0, [0, 0, 650, 500], [], [], [], [], [], kPsychGUIWindow + kPsychGUIWindowWMPositioned); %#ok<AGROW>
        
        % Set text size for info text:
        Screen('TextSize', win(i), 24);
        
        % Open i'th camera:
        grabbers(i) = Screen('OpenVideoCapture', win(i), deviceIds(i), roi, depth, 64, [], codec, captureFlags, [], bitdepth); %#ok<AGROW>
        
        if i == 1
            % Reset firewire bus for this camera:
            % Screen('SetVideoCaptureParameter', grabbers(i), 'ResetBus');
            
            % Reset this camera:
            %Screen('SetVideoCaptureParameter', grabbers(i), 'ResetCamera');
        end
        
        % Multi-camera sync mode requested?
        if syncmode > 0
            if i == 1
                % First one is sync-master: Unless noMaster == 1, in which case there are only slaves.
                Screen('SetVideoCaptureParameter', grabbers(1), 'SyncMode', syncmode + 1 + noMaster);
                if Screen('SetVideoCaptureParameter', grabbers(1), 'SyncMode') ~= (syncmode + 1 + noMaster)
                    error('Sync master camera does not support requested sync mode %i! Game over!', syncmode);
                end
            else
                % Others are sync-slaves:
                Screen('SetVideoCaptureParameter', grabbers(i), 'SyncMode', syncmode + 2);
                if Screen('SetVideoCaptureParameter', grabbers(i), 'SyncMode') ~= syncmode + 2
                    % This slave does not support syncmode! Means the syncmode must be hardware sync,
                    % as that is the only one which can be unsupported. Fall back to bus sync and switch
                    % master into combined hw sync + bus sync mode:
                    fprintf('Sync slave camera %i does not support requested sync mode %i!\n', grabbers(i), syncmode);
                    
                    % Hardware sync requested but unsupported by this slave?
                    if (syncmode == 16) && ~noMaster
                        % Yes, workaround via additional bus-sync and hope for the best:
                        fprintf('Switching sync slave camera %i to bus sync as fallback. Master will emit bus-sync signals too.\n', grabbers(i));
                        % Set slave to bus sync:
                        Screen('SetVideoCaptureParameter', grabbers(i), 'SyncMode', 8 + 2);
                        % Set master to bus sync in addition to hw sync:
                        Screen('SetVideoCaptureParameter', grabbers(1), 'SyncMode', 16 + 8 + 1);
                    end
                end
            end
        end
        
        % Use TriggerMode 0 "Start of exposure by trigger, duration of exposure by 'Shutter' setting". Trigger exposure on falling edge,
        % (active low TriggerPolarity), get signal from TriggerSource 0, aka port 0:
        fprintf('Camera %i : OldTriggerMode = %i\n', grabbers(i), Screen('SetVideoCaptureParameter', grabbers(i), 'TriggerMode', 0));
        fprintf('Camera %i : OldTriggerPolarity = %i\n', grabbers(i), Screen('SetVideoCaptureParameter', grabbers(i), 'TriggerPolarity', 0));
        fprintf('Camera %i : OldTriggerSource = %i\n', grabbers(i), Screen('SetVideoCaptureParameter', grabbers(i), 'TriggerSource', 0));
        fprintf('Camera %i : TriggerSources = ', grabbers(i)); disp(Screen('SetVideoCaptureParameter', grabbers(i), 'GetTriggerSources'));
        
        % Configure i'th camera:
        %brightness = Screen('SetVideoCaptureParameter',  grabbers(i), 'Brightness',383)
        %exposure = Screen('SetVideoCaptureParameter',  grabbers(i), 'Exposure',130)
        %gain = Screen('SetVideoCaptureParameter',  grabbers(i), 'Gain')
        %gamma = Screen('SetVideoCaptureParameter',  grabbers(i), 'Gamma')
        %shutter = Screen('SetVideoCaptureParameter',  grabbers(i), 'Shutter', 7)
        %vendor = Screen('SetVideoCaptureParameter',  grabbers(i), 'GetVendorname')
        %model  = Screen('SetVideoCaptureParameter',  grabbers(i), 'GetModelname')
        %fps  = Screen('SetVideoCaptureParameter',  grabbers(i), 'GetFramerate')
        %roi  = Screen('SetVideoCaptureParameter',  grabbers(i), 'GetROI')
        
        %bmode = Screen('SetVideoCaptureParameter',  grabbers(i), '1394BModeActive', 0)
        %isospeed = Screen('SetVideoCaptureParameter',  grabbers(i), 'ISOSpeed', 400)
        
        %pio = Screen('SetVideoCaptureParameter',  grabbers(i), 'PIO', 1)
        %pio = Screen('SetVideoCaptureParameter',  grabbers(i), 'PIO')
        
        %[targetTemperature, currentTemperature] = Screen('SetVideoCaptureParameter',  grabbers(i), 'Temperature', 123)
        %[u,v] = Screen('SetVideoCaptureParameter',  grabbers(i), 'WhiteBalance', 161, 116)
        %[u,v] = Screen('SetVideoCaptureParameter',  grabbers(i), 'WhiteBalance')
        
        %[wr, wg, wb] = Screen('SetVideoCaptureParameter',  grabbers(i), 'WhiteShading')
        
        % Measure firewire bus cycles for fun and profit :-)
        [cycleSecs1, cycleSystemTime1, cycleSec, cycleCount, cycleOffset] = Screen('SetVideoCaptureParameter',  grabbers(i), 'GetCycleTimer');
        WaitSecs(0.1);
        [cycleSecs2, cycleSystemTime2] = Screen('SetVideoCaptureParameter',  grabbers(i), 'GetCycleTimer');
        fprintf('Camera %i: Bus runs at %f seconds per second.\n', grabbers(i), (cycleSecs2 - cycleSecs1) / (cycleSystemTime2 - cycleSystemTime1));
        fprintf('Camera %i: Initial bus timestamps were cycleSec %i, cycleCount %i, cycleOffset %i.\n', grabbers(i), cycleSec, cycleCount, cycleOffset);
        
        % Basler camera?
        if strfind(Screen('SetVideoCaptureParameter', grabbers(i), 'GetVendorname'), 'Basler')
            % Yes. Enable some Basler specific SFF features:
            
            % The Basler SFF framecounter is mostly useless to us, as it only resets to zero on a power-cycle,
            % and the cameras can't get power-cycled in software, only by physical unplug/replug :(.
            % Update: Some Basler cameras allow power-cycling, so it does work on those, e.g., the A602f works,
            % but the A312fc doesn't.
            % baslerFrameCounter = Screen('SetVideoCaptureParameter', grabbers(i), 'BaslerFrameCounterEnable')
            
            % Basler SFF CRC checksumming can find corrupted video frames due to problems with camera electronics,
            % bus cables, controllers, OS etc. It is very compute intense though, adds easily 10 msecs per frame,
            % so one should probably only enable it to diagnose real problems or initially verify a setup:
            % baslerChecksum = Screen('SetVideoCaptureParameter', grabbers(i), 'BaslerChecksumEnable')
            
            % Basler SFF timestamping can theoretically provide a capture timestamp corresponding to the exact
            % time when image exposure on the cameras sensor was started. The camera can tag frames with the
            % firewire bus time of start of exposure and Screen() can translate that into GetSecs time.
            %
            % In practice, all two tested models of Basler cameras didn't work. They returned a constant
            % bogus value as timestamp, leading to bogus capture timestamps. No bug could be found in our code
            % or the libdc1394 code when comparing code against the Basler SFF spec documents.
            % baslerTimestamp = Screen('SetVideoCaptureParameter', grabbers(i), 'BaslerFrameTimestampEnable')
        end
        
        Screen('SetVideoCaptureParameter', grabbers(i), 'PrintParameters')
        
        % Select convMode as conversion mode:
        Screen('SetVideoCaptureParameter', grabbers(i), 'DataConversionMode', convMode);
        
        % Set an override bayer pattern to use if it can't get auto-detected:
        Screen('SetVideoCaptureParameter', grabbers(i), 'OverrideBayerPattern', bayerPattern);
        
        % Select debayer algorithm:
        Screen('SetVideoCaptureParameter', grabbers(i), 'DebayerMethod', debayerMethod);
        
        % Ask engine to prefer Format-7 video capture modes over bog-standard Non-Format-7 ones.
        % Normally the engine decides itself what is the best choice. Forcing the engine to
        % use Format-7 sometimes allows to save a bit of bus-bandwidth and thereby squeeze out
        % higher framerates, resolutions or use of more cameras on a single bus in multi-cam capture.
        Screen('SetVideoCaptureParameter', grabbers(i), 'PreferFormat7Modes', 1);
        
        if doVideoRecording
            % If video recording is requested, set a unique movie filename per camera:
            Screen('SetVideoCaptureParameter', grabbers(i), sprintf('SetNewMoviename=%s_Cam%02d.mov', movieName, grabbers(i)));
        end
        
        % If a specific maximum framecount is requested for end of capture/recording, set it here
        % before capture gets started:
        % Setting the count for the slaves it not always neccessary, as the master will distribute
        % its limit to its slaves in many common scenarios, but then "better safe than sorry".
        if maxTargetFrameCount > 0
            Screen('SetVideoCaptureParameter', grabbers(i), 'StopAtFramecount', maxTargetFrameCount);
            fprintf('Targetting stop of capture on camera %i at target framecount %i.\n', grabbers(i), maxTargetFrameCount);
        end
        
        % Assign GStreamer post processing string, if any:
        if ~isempty(processingString)
            Screen('SetVideoCaptureParameter', grabbers(i), sprintf('SetGStreamerProcessingPipeline=%s', processingString));
        end
        
        % Load and setup markertracker plugin:
        pluginPath = [MFRoot 'MFBasic/Octave3LinuxFiles64/ptbvideomarkertrackerplugin.so'];
        Screen('SetVideoCaptureParameter', grabbers(i), sprintf('LoadMarkerTrackingPlugin=%s', pluginPath));
        Screen('SetVideoCaptureParameter', grabbers(i), sprintf('SendCommandToMarkerTrackingPlugin=CMD_TRACKERCAMID %i', 0));
        Screen('SetVideoCaptureParameter', grabbers(i), 'SendCommandToMarkerTrackingPlugin=CMD_UDPSTREAMTO localhost');
    end
    
    % Start capture on all cameras:
    if syncmode == 0
        % Start one after the other:
        for grabber=grabbers
            Screen('StartVideoCapture', grabber, fps, dropframes);
        end
    else
        % Multicam sync enabled. First start all slaves:
        oldverb = Screen('Preference','Verbosity', 4);
        fprintf('Prepare for synced start! Warp 1 ...\n\n');
        for grabber=grabbers(2:end)
            Screen('StartVideoCapture', grabber, fps, dropframes);
        end
        
        % Only wait for keypress if there is a designated master. With
        % only slaves, that wait would be futile:
        if ~noMaster
            KbStrokeWait;
        end
        fprintf('Engage! ...\n\n');
        
        % Start master:
        Screen('StartVideoCapture', grabbers(1), fps, dropframes);
        fprintf('And we are flying!\n\n');
        Screen('Preference','Verbosity', oldverb);
    end
    
    % If a specific maximum framecount is requested for end of capture/recording, set it here dynamically
    % while capture is already started:
    if maxTargetFrameCount < 0
        % For maximum robustness one should set the count for all slaves first, before the master:
        % Setting the count for the slaves it not always neccessary, as the master will distribute
        % its limit to its slaves in many common scenarios, but then "better safe than sorry".
        for grabber = grabbers(2:end)
            Screen('SetVideoCaptureParameter', grabber, 'StopAtFramecount', abs(maxTargetFrameCount));
        end
        
        % Finally set master / first grabber:
        Screen('SetVideoCaptureParameter', grabbers(1), 'StopAtFramecount', abs(maxTargetFrameCount));
        fprintf('Targetting stop of capture at target framecount %i.\n', abs(maxTargetFrameCount));
    end
    
    capturestopped = 0;
    dstRect = [];
    count = 0;
    oldpts = zeros(size(grabbers));
    texcount = zeros(size(grabbers));
    camtex = zeros(length(grabbers), fps * 10);
    campts = zeros(size(camtex));
    t=GetSecs;
    
    % Multicapture and display loop: Runs until timeout of 120 seconds or until keypress
    % if there isn't any master cam or if no recording is requested:
    while dropframes || noMaster || ((GetSecs - t) < 120)
        if KbCheck
            if ~capturestopped
                capturestopped = 1;
                maxTargetFrameCount = Screen('SetVideoCaptureParameter', grabbers(1), 'GetFutureMaxFramecount');
                fprintf('Logically stopping capture on master by setting stop frame count to current maximum framecount %i!\n', maxTargetFrameCount);
                Screen('SetVideoCaptureParameter', grabbers(1), 'StopAtFramecount', maxTargetFrameCount);
                fprintf('Capture on master scheduled to stop.\n');
                KbReleaseWait;
            else
                break;
            end
        end
        
        for i=1:length(grabbers)
            [tex pts nrdropped] = Screen('GetCapturedImage', win(i), grabbers(i), 0); %#ok<NASGU>
            % fprintf('tex = %i  pts = %f nrdropped = %i\n', tex, pts, nrdropped);
            
            if tex > 0
                % Draw new texture from framegrabber.
                Screen('DrawTexture', win(i), tex, [], dstRect);
                
                % Print pts:
                Screen('DrawText', win(i), sprintf('%.4f    [%i of %i]', pts - t, Screen('SetVideoCaptureParameter', grabbers(i), 'GetFetchedFramecount'), Screen('SetVideoCaptureParameter', grabbers(i), 'GetCurrentFramecount')), ...
                    0, 0, [1 0 0]);
                if count > 0
                    % Compute delta:
                    delta = (pts - oldpts(i)) * 1000;
                    Screen('DrawText', win(i), sprintf('%.4f', delta), 0, 20, [1 0 0]);
                end
                oldpts(i) = pts;
                
                % Show it. Don't sync to video refresh at all, as it would cause
                % performance degradation due to lockstep between window updates.
                Screen('Flip', win(i), [], [], 2);
                if dropframes
                    Screen('Close', tex);
                else
                    texcount(i) = texcount(i) + 1; %#ok<UNRCH>
                    camtex(i, texcount(i)) = tex;
                    campts(i, texcount(i)) = pts;
                end
                tex = 0; %#ok<NASGU>
            end
            count = count + 1;
        end
        % WaitSecs('YieldSecs', 0.030);
    end
    
    telapsed = GetSecs - t;
    fprintf('Elapsed runtime %f seconds.\n', telapsed);
    
    for grabber=grabbers
        fprintf('Camera %i : Bandwidth = %f\n', grabber, Screen('SetVideoCaptureParameter', grabber, 'GetBandwidthUsage'));
        fprintf('Camera %i : UsedTriggerMode = %i\n', grabber, Screen('SetVideoCaptureParameter', grabber, 'TriggerMode'));
        fprintf('Camera %i : UsedTriggerPolarity = %i\n', grabber, Screen('SetVideoCaptureParameter', grabber, 'TriggerPolarity'));
        fprintf('Camera %i : UsedTriggerSource = %i\n', grabber, Screen('SetVideoCaptureParameter', grabber, 'TriggerSource'));
    end
    
    % Stop all cameras:
    if syncmode == 0
        % Unsynchronized operation: Stop one after the other:
        for grabber=grabbers
            Screen('StopVideoCapture', grabber);
        end
    else
        % Multicam sync enabled.
        
        % First some feedback about sync:
        for grabber=grabbers
            fprintf('Camera %i : Possible max framecount = %i\n', grabber, Screen('SetVideoCaptureParameter', grabber, 'GetFutureMaxFramecount'));
        end
        
        % Stop master first:
        fprintf('Drop us out of warp!\n');
        Screen('StopVideoCapture', grabbers(1));
        
        % Then stop all slaves:
        fprintf('Sublight reached ...\n');
        for grabber=grabbers(2:end)
            Screen('StopVideoCapture', grabber);
        end
        
        fprintf('And quarter impulse ahead.\n');
    end
    
    % Close down cameras, and some final stats:
    for grabber=grabbers
        fprintf('Camera %i : Final framecount = %i\n', grabber, Screen('SetVideoCaptureParameter', grabber, 'GetCurrentFramecount'));
        fprintf('Camera %i : Possible framecount = %i\n', grabber, Screen('SetVideoCaptureParameter', grabber, 'GetFutureMaxFramecount'));
        fprintf('Camera %i : Corrupted frames count = %i\n', grabber, Screen('SetVideoCaptureParameter', grabber, 'GetCorruptFramecount'));
        Screen('CloseVideoCapture', grabber);
    end
    
    if ~dropframes
        fi = 1;
        while 1
            [secs, keyCode] = KbWait; %#ok<ASGLU>
            if keyCode(escape)
                break;
            end
            
            if keyCode(backKey)
                fi = max(1, fi - 1);
            end
            
            if keyCode(forwardKey)
                fi = min(min(texcount), fi + 1);
            end
            
            for i=1:length(grabbers)
                % Draw new texture from framegrabber.
                Screen('DrawTexture', win(i), camtex(i, fi), [], dstRect);
                
                % Print pts:
                Screen('DrawText', win(i), sprintf('%.4f', campts(i, fi) - t), 0, 0, [1 0 0]);
                
                % Show it:
                Screen('Flip', win(i), [], [], 1);
            end
        end
    end
    
    % Close all textures explicitely to avoid "many open textures" warning:
    Screen('Close');
    
    % Close all windows and release all remaining display resources:
    Screen('CloseAll');
    Screen('Preference', 'SkipSyncTests', oldsynctests);
catch %#ok<*CTCH>
    % Emergency shutdown:
    sca;
    Screen('Preference', 'SkipSyncTests', oldsynctests);
    psychrethrow(psychlasterror);
end