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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 !

• Can you insert text from a file in real time with ffmpeg streaming ?

  6 décembre 2020, par Fight Fire With Fire

  I have this code i use to stream a file and place the name of the show of the video at a certain time of the video ( name_of_show ) at the top of the screen, and the bottom of the screen it take the name of the show from video_title.txt and places it on the bottom of the screen.

  


  What I want to do is find a way at a interval say 1 or 2 minutes, pull whatever text is currently in video_title.txt and place it in the video for a few seconds.

  


  I would update video_title.txt from another python program. Here's my current code below.

  


             command = [
        "ffmpeg" , "-re" , "-i" , video[0] ,
        "-vf" ,  "[in]drawtext=fontsize=40:fontcolor=white:box=1:boxcolor=black@0.8:boxborderw=5:fontfile=/home/fonts/timeless.ttf: text='" + name_of_show + "':x='W-(W+tw)*mod(t\,10)/10':y='H/20':enable='between(t,50,70)',drawtext=fontsize=20:fontfile=/home/fonts/timeless.ttf:textfile=/video_title.txt:fontcolor=white:box=1:boxcolor=black@0.8:boxborderw=5:x=W-w+5:y=h-th-50:enable='1'[out]"
        "-vcodec" , "libx264", "-pix_fmt", "yuv420p",
        "-preset" , "medium" , "-r" , "30" , "-g" , "48" , "-b:v" , "2500k" ,
        "-acodec" , "libmp3lame" , "-ar" , "44100", "-threads" , "6" ,
        "-q:a" , "3" , "-b:a" , "712000" ,"-bufsize", "512k" , "-f" ,
        "flv" , STREAM_URL,


  


  Ultimately the effect I am trying to achieve is a long stream of lets say 1 hour on twitch/youtube where someone could send a text message and it would appear in the stream.

  


• Encoding real, source duration of a timelapse into MP4 container using FFMPEG (GoPro) [closed]

  13 août 2024, par Marek Towarek

  Footage recorded with GoPro TimeLapse / TimeWarp, indicates the total, real-time duration of recorded data, while the video stream is of reduced length by the timelapse interval.

  


  General
Complete name               : E:\Video\GoPro\GoPro\GH010656.MP4
Format                      : MPEG-4
Format profile              : Base Media / Version 1
Codec ID                    : mp41 (mp41)
File size                   : 1.94 GiB
Duration                    : 22 min 55 s
Overall bit rate mode       : Variable
Overall bit rate            : 12.1 Mb/s

Video
ID                          : 1
Format                      : AVC
Format/Info                 : Advanced Video Codec
Format profile              : High@L5
Format settings             : CABAC / 2 Ref Frames
Format settings, CABAC      : Yes
Format settings, Reference  : 2 frames
Format settings, GOP        : M=1, N=15
Codec ID                    : avc1
Codec ID/Info               : Advanced Video Coding
Duration                    : 4 min 35 s
Bit rate mode               : Variable
Bit rate                    : 60.0 Mb/s
Width                       : 1 920 pixels
Height                      : 1 440 pixels
Display aspect ratio        : 4:3
Rotation                    : 180°
Frame rate mode             : Constant
Frame rate                  : 29.970 (30000/1001) FPS
Color space                 : YUV
Chroma subsampling          : 4:2:0
Bit depth                   : 8 bits
Scan type                   : Progressive
Bits/(Pixel*Frame)          : 0.724
Stream size                 : 1.92 GiB (99%)
Title                       : GoPro AVC  
Language                    : English
Color range                 : Limited
colour_range_Original       : Full
Color primaries             : BT.709
Transfer characteristics    : BT.709
Matrix coefficients         : BT.709
Codec configuration box     : avcC

Other #1
ID                          : 2
Type                        : Time code
Format                      : QuickTime TC
Duration                    : 4 min 35 s
Bit rate mode               : Constant
Frame rate                  : 29.970 (30000/1001) FPS
Title                       : GoPro TCD  
Language                    : English

Other #2
Type                        : meta
Duration                    : 22 min 55 s
Source duration             : 4 min 35 s
Bit rate mode               : Variable
Stream size                 : 15.0 MiB
Source stream size          : 15.0 MiB


  


  This information could be omitted.
  
But it becomes quite important for correctness of GPS Data stored in Stream #2.

  


  Unfortunately, all the settings I have tried for FFMPEG, do not preserve the duration of Stream #2.
& the output ends up looking like this :

  


  General
Complete name               : C:\Video_Encode\GoPro\GH010656.mp4
Format                      : MPEG-4
Format profile              : Base Media
Codec ID                    : isom (isom/iso2/mp41)
File size                   : 717 MiB
Duration                    : 4 min 35 s
Overall bit rate            : 21.9 Mb/s
Encoded date                : UTC 2026-03-29 11:28:23
Tagged date                 : UTC 2026-03-29 11:28:23
Writing application         : Lavf61.5.101

Video
ID                          : 1
Format                      : HEVC
Format/Info                 : High Efficiency Video Coding
Format profile              : Main@L5@Main
Codec ID                    : hvc1
Codec ID/Info               : High Efficiency Video Coding
Duration                    : 4 min 35 s
Bit rate                    : 21.4 Mb/s
Width                       : 1 920 pixels
Height                      : 1 440 pixels
Display aspect ratio        : 4:3
Frame rate mode             : Constant
Frame rate                  : 29.970 (30000/1001) FPS
Color space                 : YUV
Chroma subsampling          : 4:2:0 (Type 0)
Bit depth                   : 8 bits
Scan type                   : Progressive
Bits/(Pixel*Frame)          : 0.258
Stream size                 : 702 MiB (98%)
Title                       : GoPro AVC  
Writing library             : x265 3.6+35-dd594f59d:[Windows][GCC 14.1.0][64 bit] 8bit+10bit+12bit
Language                    : English
Encoded date                : UTC 2026-03-29 11:28:23
Tagged date                 : UTC 2026-03-29 11:28:23
Color range                 : Full
Color primaries             : BT.709
Transfer characteristics    : BT.709
Matrix coefficients         : BT.709
Codec configuration box     : hvcC

Other #1
ID                          : 2
Type                        : Time code
Format                      : QuickTime TC
Duration                    : 4 min 35 s
Frame rate                  : 29.970 (30000/1001) FPS
Time code of first frame    : 17:55:35:02
Time code of last frame     : 18:00:09:28
Time code, stripped         : Yes
Title                       : GoPro TCD  
Language                    : English
Default                     : Yes
Alternate group             : 2
Encoded date                : UTC 2026-03-29 11:28:23
Tagged date                 : UTC 2026-03-29 11:28:23
mdhd_Duration               : 275175

Other #2
Type                        : meta
Duration                    : 4 min 35 s
Bit rate mode               : Variable


  


  Any ideas how to preserve that real time duration indicator ?
  
Here is the FFMPEG binary I use to get the TMCD & GMPD data to copy : GitHub Link