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• QSharedMemory in Real-Time process

  21 novembre 2016, par Seungsoo Kim

  I’m trying to use QSharedMemory Class to share video data between two processes.

  So I tried like following method, but it has problem in simultaneous access of two processes.

  Two process crashes when they access sequentially to same memory name(key) "SharedMemory".

  I locked them while they’re used, but also it doesn’t work well.

  How can i avoid this crash ??

  1. Writing to SharedMemory - data type is and this function called by callback.

     QBuffer buffer;
     
     buffer.open(QBuffer::ReadWrite);
     
     QDataStream out(&buffer);
     
     
     
     QByteArray outArray = QByteArray::fromRawData(reinterpret_cast<const>(data), strlen(reinterpret_cast<const>(data)));
     
     out &lt;&lt; width &lt;&lt; height &lt;&lt; step &lt;&lt; cameraId &lt;&lt; strlen(reinterpret_cast<const>(data));
     
     out.writeRawData(outArray.data(), outArray.size());
     
     
     
     int size = buffer.size();
     
     
     
     sharedMemory.setKey("SharedMemory");
     
     
     
     if (!sharedMemory.isAttached()) {
     
         printf("Cannot attach to shared memory to update!\n");
     
     }
     
     if (!sharedMemory.create(size))
     
     {
     
         printf("failed to allocate memory\n");
     
     }
     
     sharedMemory.lock();
     
     char *to = (char*)sharedMemory.data();
     
     const char *from = buffer.data().data();
     
     memcpy(to, from,qMin(sharedMemory.size(),size));
     
     sharedMemory.unlock();
     
     </const></const></const>

  2. Using data in SharedMemory. - this function is called by QThread, interval 100ms

     QSharedMemory sharedMemory("SharedMemory");
     
     sharedMemory.lock();
     
     if (!sharedMemory.attach()) {
     
         printf("failed to attach to memory\n");
     
         return;
     
     }
     
     
     
     QBuffer buffer;
     
     QDataStream in(&buffer);
     
     
     
     sharedMemory.create(1920 * 1080);
     
     buffer.setData((char*)sharedMemory.constData(), sharedMemory.size());
     
     buffer.open(QBuffer::ReadOnly);
     
     sharedMemory.unlock();
     
     sharedMemory.detach();
     
     
     
     int r_width = 0;    
     
     int r_height = 0;
     
     int r_cameraId = 0;
     
     int r_step = 0;
     
     int r_strlen = 0;
     
     in >> r_width >> r_height >> r_step >> r_cameraId >> r_strlen;
     
     
     
     char* receive = new char[r_strlen];
     
     in.readRawData(receive, r_strlen);
     
     //unsigned char* r_receive = new unsigned char[r_strlen];
     
     //r_receive = (unsigned char*)receive;
     
     
     
     QPixmap backBuffer = QPixmap::fromImage(QImage((unsigned char*)receive, r_width, r_height, r_step, QImage::Format::Format_RGB888));
     
     ui.label->setPixmap(backBuffer.scaled(ui.label->size(), Qt::KeepAspectRatio));
     
     ui.label->show();

  please share your idea ! thank you !

• ffmpeg generating out of sync audio/video file

  2 mars 2013, par marcelorocks

  I am trying to convert a flv video to mp4 using a264, but the result video has a out of sync audio/video. Audio seems ok but video seems slow and therefore out of sync. I am a newbie on video conversion so any help is appreciated.

  Here is the command I am running :

  /opt/local/bin/ffmpeg -i complaint.flv -f mp4 -vcodec libx264 -acodec aac -copyts -strict experimental -fpre /opt/local/share/ffmpeg/libx264-lossless_slow.ffpreset -ab 44k -threads 0 -crf 23 complaint.mp4

  And the printout :

  Desktop  /opt/local/bin/ffmpeg -i complaint.flv -f mp4 -vcodec libx264 -acodec aac -copyts -strict experimental -fpre /opt/local/share/ffmpeg/libx264-lossless_slow.ffpreset -ab 44k -threads 0 -crf 23 complaint.mp4
  
  ffmpeg version 0.7.8, Copyright (c) 2000-2011 the FFmpeg developers
  
    built on Jan 12 2012 21:12:26 with gcc 4.2.1 (Apple Inc. build 5666) (dot 3)
  
    configuration: --prefix=/opt/local --enable-gpl --enable-postproc --enable-swscale --enable-avfilter --enable-libmp3lame --enable-libvorbis --enable-libtheora --enable-libdirac --enable-libschroedinger --enable-libopenjpeg --enable-libxvid --enable-libx264 --enable-libvpx --enable-libspeex --mandir=/opt/local/share/man --enable-shared --enable-pthreads --cc=/usr/bin/gcc-4.2 --arch=x86_64 --enable-yasm
  
    libavutil    50. 43. 0 / 50. 43. 0
  
    libavcodec   52.123. 0 / 52.123. 0
  
    libavformat  52.111. 0 / 52.111. 0
  
    libavdevice  52.  5. 0 / 52.  5. 0
  
    libavfilter   1. 80. 0 /  1. 80. 0
  
    libswscale    0. 14. 1 /  0. 14. 1
  
    libpostproc  51.  2. 0 / 51.  2. 0
  
  [flv @ 0x7fe57a04ac00] Estimating duration from bitrate, this may be inaccurate
  
  Input #0, flv, from 'complaint.flv':
  
    Metadata:
  
      duration        : 7
  
      creationdate    : Thu Jan 12 23:47:24
  
      description     : Recorded using VideoRecording example.
  
    Duration: 00:00:06.61, start: 0.000000, bitrate: N/A
  
      Stream #0.0: Video: flv, yuv420p, 288x288, 1k tbr, 1k tbn, 1k tbc
  
      Stream #0.1: Audio: nellymoser, 11025 Hz, mono, s16
  
  File 'complaint.mp4' already exists. Overwrite ? [y/N] y
  
  [buffer @ 0x7fe579c32cc0] w:288 h:288 pixfmt:yuv420p tb:1/1000000 sar:0/1 sws_param:
  
  [libx264 @ 0x7fe57a044600] using cpu capabilities: none!
  
  [libx264 @ 0x7fe57a044600] profile High, level 4.2
  
  [libx264 @ 0x7fe57a044600] 264 - core 118 - H.264/MPEG-4 AVC codec - Copyleft 2003-2011 - http://www.videolan.org/x264.html - options: cabac=1 ref=2 deblock=1:0:0 analyse=0x3:0x33 me=umh subme=6 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=6 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.41 aq=1:1.00
  
  Output #0, mp4, to 'complaint.mp4':
  
    Metadata:
  
      duration        : 7
  
      creationdate    : Thu Jan 12 23:47:24
  
      description     : Recorded using VideoRecording example.
  
      encoder         : Lavf52.111.0
  
      Stream #0.0: Video: libx264, yuv420p, 288x288, q=0-69, 200 kb/s, 1k tbn, 1k tbc
  
      Stream #0.1: Audio: aac, 11025 Hz, mono, s16, 44 kb/s
  
  Stream mapping:
  
    Stream #0.0 -> #0.0
  
    Stream #0.1 -> #0.1
  
  Press [q] to stop, [?] for help
  
  frame= 6557 fps=106 q=-1.0 Lsize=     685kB time=00:00:03.62 bitrate=1549.1kbits/s dup=6367 drop=0    
  
  video:615kB audio:17kB global headers:0kB muxing overhead 8.361360%
  
  frame I:27    Avg QP:19.98  size:  8242
  
  [libx264 @ 0x7fe57a044600] frame P:6530  Avg QP:30.71  size:    62
  
  [libx264 @ 0x7fe57a044600] mb I  I16..4: 11.1% 79.3%  9.6%
  
  [libx264 @ 0x7fe57a044600] mb P  I16..4:  0.1%  0.2%  0.0%  P16..4:  1.2%  0.2%  0.3%  0.0%  0.0%    skip:98.0%
  
  [libx264 @ 0x7fe57a044600] 8x8 transform intra:77.8% inter:64.9%
  
  [libx264 @ 0x7fe57a044600] coded y,uvDC,uvAC intra: 75.3% 81.3% 33.3% inter: 0.5% 0.7% 0.1%
  
  [libx264 @ 0x7fe57a044600] i16 v,h,dc,p: 78%  9% 10%  3%
  
  [libx264 @ 0x7fe57a044600] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 35% 11% 32%  3%  4%  5%  2%  5%  4%
  
  [libx264 @ 0x7fe57a044600] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 56%  7%  9%  3%  4%  7%  3%  7%  3%
  
  [libx264 @ 0x7fe57a044600] i8c dc,h,v,p: 45% 15% 34%  6%
  
  [libx264 @ 0x7fe57a044600] Weighted P-Frames: Y:0.0% UV:0.0%
  
  [libx264 @ 0x7fe57a044600] ref P L0: 80.5%  9.5% 10.0%
  
  [libx264 @ 0x7fe57a044600] kb/s:767.20

• FFMPEG support for HLS v4 and v5

  5 février 2015, par omkar

  As I understand latest FFMPEG version 2.0.1 supports till HLS version 3.

  After going through draft specifications for HLS :

  New features introduced in HLS V4 are :

  • Segments with bit range support with tag EXT-X-BYTERANGE
  • Support for fast forward and fast rewind with tags EXT-X-I-FRAMES-ONLY and EXT-X-I-FRAME-STREAM-INF
  • Alternate media option with tag EXT-X-MEDIA

  New features introduced in HLS V5 are :

  • Introduction of new attributes KEYFORMAT and KEYFORMATVERSIONS for tag EXT-X-KEY
  • Introduction of tag EXT-X-MAP
  • Support for subtitles by introduction of SUBTITLES value for attribute TYPE of tag EXT-X-MEDIA.

  Wanted to know which of the above features are planned to be implemented in FFMPEG library in near future ? It will be great if you share the expected delivery dates or versions for these features.

  Thanks in advance.