Error while recording multiple screens using AVFoundation

Question

Hi All,
I am trying to record primary and secondary monitor screens into two separate files using below code.
const uint32_t MAX_DISPLAY = 2;
CGDirectDisplayID displays[MAX_DISPLAY] = {0};
CGGetActiveDisplayList(MAX_DISPLAY, displays, &m_nDisplays);
NSString* dest_file[2] = {0};
NSURL* dest_path[2] = {0};
AVCaptureConnection *CaptureConnection[2] = {0};
NSDictionary *videoCleanApertureSettings = [NSDictionary dictionaryWithObjectsAndKeys:
   @2048, AVVideoCleanApertureWidthKey,
   @1152, AVVideoCleanApertureHeightKey,
   @0, AVVideoCleanApertureHorizontalOffsetKey,
   @0, AVVideoCleanApertureVerticalOffsetKey,
  nil];
NSDictionary *videoAspectRatioSettings = [NSDictionary dictionaryWithObjectsAndKeys:
   @3,AVVideoPixelAspectRatioHorizontalSpacingKey,
   @3,AVVideoPixelAspectRatioVerticalSpacingKey,
  nil];
NSNumber* bitsPerSecond = [NSNumber numberWithDouble:1024*1000];
NSDictionary *codecSettings =  [NSDictionary dictionaryWithObjectsAndKeys:
  bitsPerSecond, AVVideoAverageBitRateKey,
  videoCleanApertureSettings, AVVideoCleanApertureKey,
  videoAspectRatioSettings, AVVideoPixelAspectRatioKey,
  nil];
NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
   AVVideoCodecH264, AVVideoCodecKey,
  codecSettings,AVVideoCompressionPropertiesKey,
   AVVideoScalingModeResize,AVVideoScalingModeKey,
   @2048, AVVideoWidthKey,
   @1152, AVVideoHeightKey,
  nil];
for( int nIdx = 0; nIdx < m_nDisplays; ++nIdx )
  m_session[nIdx] = [[AVCaptureSession alloc] init];
  dest_file[nIdx] = [NSString stringWithFormat:@"%@_%d.MOV",destination_path,nIdx];
  dest_path[nIdx] = [NSURL fileURLWithPath: dest_file[nIdx] ];
   // Create a ScreenInput with the display and add it to the session
  m_movie_file_input[nIdx] = [[[AVCaptureScreenInput alloc] initWithDisplayID:displays[nIdx]] autorelease];  
   [m_movie_file_input[nIdx] removesDuplicateFrames ];
   if ([m_session[nIdx] canAddInput:m_movie_file_input[nIdx]])
   [m_session[nIdx] addInput:m_movie_file_input[nIdx]];
   // Create a MovieFileOutput and add it to the session
  m_movie_file_output[nIdx] = [[[AVCaptureMovieFileOutput alloc] init] autorelease];
   if ([m_session[nIdx] canAddOutput:m_movie_file_output[nIdx]])
   [m_session[nIdx] addOutput:m_movie_file_output[nIdx]];
   CaptureConnection[nIdx] = [m_movie_file_output[nIdx] connectionWithMediaType:AVMediaTypeVideo];
   [m_movie_file_output[nIdx] setOutputSettings : videoSettings forConnection : CaptureConnection[nIdx]];
   // Start running the session
   [m_session[nIdx] startRunning];
   [m_movie_file_output[nIdx] startRecordingToOutputFileURL:dest_path[nIdx]  recordingDelegate:self];
I am getting both the screens saved into two separate files. But while calling startRecordingToOutputFileURL API for the secondary monitor i.e. for the second pass of loop, I am getting an error as shown below :
VTCompressionSessionCreate signalled err=-8973 (err) (VTVideoEncoderStartSession failed) at /SourceCache/CoreMedia_frameworks/CoreMedia-1562.19/Sources/VideoToolbox/VTComp ressionSession.c line 897
Also compression parameters(bitrate) are not setting properly for Secondary monitor, it takes some different values other than the one I have specified in the program.
Can somebody please help me on this ? Also please let me know this is the proper way of doing this.
Thanks in Advance
George

Answer 1

Hi,
Check the following link:
http://www.sap-img.com/bapi.htm
Regards,
Bhaskar