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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 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.

• Encoder (codec vp8) not found [closed]

  25 juillet 2020, par Nirav Trivedi

  There was a problem !

  


  ffmpeg -i uploads/155799695.wav -i uploads/155799695.webm -map 0:0 -map 1:0 uploads/155799695-merged.webm 2>&1


  


  output :

  


  [0] => ffmpeg version 2.6.8 Copyright (c) 2000-2016 the FFmpeg developers
[1] =>   built with gcc 4.4.7 (GCC) 20120313 (Red Hat 4.4.7-16)
[2] =>   configuration: --prefix=/usr --bindir=/usr/bin --datadir=/usr/share/ffmpeg --incdir=/usr/include/ffmpeg --libdir=/usr/lib64 --mandir=/usr/share/man --arch=x86_64 --optflags='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic' --enable-bzlib --disable-crystalhd --enable-gnutls --enable-ladspa --enable-libass --enable-libdc1394 --enable-libfaac --enable-nonfree --disable-indev=jack --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-openal --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libv4l2 --enable-libx264 --enable-libx265 --enable-libxvid --enable-x11grab --enable-avfilter --enable-avresample --enable-postproc --enable-pthreads --disable-static --enable-shared --enable-gpl --disable-debug --disable-stripping --shlibdir=/usr/lib64 --enable-runtime-cpudetect
[3] =>   libavutil      54. 20.100 / 54. 20.100
[4] =>   libavcodec     56. 26.100 / 56. 26.100
[5] =>   libavformat    56. 25.101 / 56. 25.101
[6] =>   libavdevice    56.  4.100 / 56.  4.100
[7] =>   libavfilter     5. 11.102 /  5. 11.102
[8] =>   libavresample   2.  1.  0 /  2.  1.  0
[9] =>   libswscale      3.  1.101 /  3.  1.101
[10] =>   libswresample   1.  1.100 /  1.  1.100
[11] =>   libpostproc    53.  3.100 / 53.  3.100
[12] => Guessed Channel Layout for  Input Stream #0.0 : stereo
[13] => Input #0, wav, from 'uploads/199606400.wav':
[14] =>   Duration: 00:00:09.01, bitrate: 1411 kb/s
[15] =>     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, 2 channels, s16, 1411 kb/s
[16] => Input #1, matroska,webm, from 'uploads/199606400.webm':
[17] =>   Metadata:
[18] =>     encoder         : Chrome
[19] =>   Duration: N/A, start: 0.000000, bitrate: N/A
[20] =>     Stream #1:0(eng): Video: vp8, yuv420p, 640x480, SAR 1:1 DAR 4:3, 12.58 tbr, 1k tbn, 1k tbc (default)
[21] =>     Metadata:
[22] =>       alpha_mode      : 1
[23] => Output #0, webm, to 'uploads/199606400-merged.webm':
[24] =>     Stream #0:0: Audio: vorbis, 0 channels, 128 kb/s
[25] =>     Metadata:
[26] =>       encoder         : Lavc56.26.100 libvorbis
[27] =>     Stream #0:1(eng): Video: vp8, none, q=2-31, 128 kb/s (default)
[28] =>     Metadata:
[29] =>       alpha_mode      : 1
[30] => Stream mapping:
[31] =>   Stream #0:0 -> #0:0 (pcm_s16le (native) -> vorbis (libvorbis))
[32] =>   Stream #1:0 -> #0:1 (vp8 (native) -> ? (?))
[33] => Encoder (codec vp8) not found for output stream #0:1