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• avformat/mpegenc : Ensure packet queue stays valid

  15 février 2021, par Andreas Rheinhardt

  avformat/mpegenc : Ensure packet queue stays valid
  The MPEG-PS muxer uses a custom queue of custom packets. To keep track
  
  of it, it has a pointer (named predecode_packet) to the head of the
  
  queue and a pointer to where the next packet is to be added (it points
  
  to the next-pointer of the last element of the queue) ; furthermore,
  
  there is also a pointer that points into the queue (called premux_packet).
  The exact behaviour was as follows : If premux_packet was NULL when a
  
  packet is received, it is taken to mean that the old queue is empty and
  
  a new queue is started. premux_packet will point to the head of said
  
  queue and the next_packet-pointer points to its next pointer. If
  
  predecode_packet is NULL, it will also made to point to the newly
  
  allocated element.
  But if premux_packet is NULL and predecode_packet is not, then there
  
  will be two queues with head elements premux_packet and
  
  predecode_packet. Yet only elements reachable from predecode_packet are
  
  ever freed, so the premux_packet queue leaks.
  
  Worse yet, when the predecode_packet queue will be eventually exhausted,
  
  predecode_packet will be made to point into the other queue and when
  
  predecode_packet will be freed, the next pointer of the preceding
  
  element of the queue will still point to the element just freed. This
  
  element might very well be still reachable from premux_packet which
  
  leads to use-after-frees lateron. This happened in the tickets mentioned
  
  below.
  Fix this by never creating two queues in the first place by checking for
  
  predecode_packet to know whether the queue is empty. If premux_packet is
  
  NULL, then it is set to the newly allocated element of the queue.
  Fixes tickets #6887, #8188 and #8266.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/mpegenc.c

• How to ensure that ffmpeg libraries uses/ not uses GPU

  31 mai 2021, par zimopisec

  My library ( Linux, Debian) uses FFMpeg libraries ( avformat, avcodec, swscale etc) for reading video stream from network cameras. Actually, I need to capture each video frame from network camera, decode it, scale and store in memory- and other thread pass this data to calling program for display.

  


  Problem is, that all works in CPU and take a huge amount of CPU resource. How can I enforce usage of GPU accelerator for processing ?

  


  I have video card : VGA compatible controller : Intel Corporation HD Graphics 620 (rev 02)

  


  My decode thread look like this ( I omit declarations, error handling etc, so pls don't look for grammar mistakes :)))

  


  fmt = avformat_alloc_context(); 
//initialising, setting option by av_dict_set
// finding video stream index
***
 // finding decoder and allocate its contexts

    frame = av_frame_alloc();

    while ( av_read_frame(ctx->fmt, &pkt) >= 0) 
    {
        AVPacket orig_pkt = pkt;

         avcodec_send_packet(ctx->dec_ctx, pkt);
         avcodec_receive_frame(ctx->dec_ctx, frame);
            *** 
// get buffer allocated for store of frame data
             buff = get_free_buffer(ctx);
        sws_scale(ctx->sws, (const uint8_t * const*)frame->data, 
        frame->linesize, 0, ctx->dec_ctx->height, buff->data,
        buff->linesize);
            ret = decode_packet(ctx, frame, &pkt, &got_frame);
            if (ret < 0)
                break;
            pkt.data += ret;
            pkt.size -= ret;
        }
        while (pkt.size > 0);

        av_packet_unref(&orig_pkt);
    }
*****  


  


• tests/fate-run : Ensure that THREADS=random is actually random

  19 septembre 2023, par Andreas Rheinhardt

  tests/fate-run : Ensure that THREADS=random is actually random
  From the documentation of GNU awk [1] :
  
  "In most awk implementations, including gawk, rand() starts generating
  
  numbers from the same starting number, or seed, each time you run awk.45
  
  Thus, a program generates the same results each time you run it. The
  
  numbers are random within one awk run but predictable from run to run.
  
  This is convenient for debugging, but if you want a program to do
  
  different things each time it is used, you must change the seed to a
  
  value that is different in each run. To do this, use srand()."
  This commit does exactly this.
  [1] : https://www.gnu.org/software/gawk/manual/html_node/Numeric-Functions.html#index-rand_0028_0029-function
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] tests/fate-run.sh