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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

• FFmpeg, access violation on av_frame_free when running though Unity

  1er février 2021, par Mockarutan

  I'm working on a video recording plugin for Unity using ffmpeg. I'm new to the video encoding domain and just got my code to work today. But I think a might have a few memory leaks and trying to fix them crashes Unity.

  



  The plugin is written i c++ (as external "C" code) and imported in a c# script in unity with a simple DllImport. Again, this is not my comfort area either, but it works.

  



  When a screen buffer is rendered, I put in a RGB24 buffer and send it to my c++ function, this one :

  



  int encode_frame(uint8_t* rgb24Data)
{
    AVFrame *frame = av_frame_alloc();
    if (!frame)
        return COULD_NOT_ALLOCATE_FRAME;

    frame->format = codec_context->pix_fmt;
    frame->width = codec_context->width;
    frame->height = codec_context->height;

    int ret = av_image_alloc(frame->data, frame->linesize, codec_context->width, codec_context->height, codec_context->pix_fmt, 32);
    if (ret < 0)
        return COULD_NOT_ALLOCATE_PIC_BUF;

    SwsContext * ctx = sws_getContext(codec_context->width, codec_context->height,
        AV_PIX_FMT_RGB24, codec_context->width, codec_context->height,
        AV_PIX_FMT_YUV420P, 0, 0, 0, 0);


    uint8_t * inData[1] = { rgb24Data };
    int inLinesize[1] = { 3 * codec_context->width };

    sws_scale(ctx, inData, inLinesize, 0, codec_context->height, frame->data, frame->linesize); // From RGB to YUV

    frame->pts = frame_counter++;

    ret = avcodec_send_frame(codec_context, frame);
    if (ret < 0)
        return ERROR_ENCODING_FRAME_SEND;

    AVPacket pkt;
    av_init_packet(&pkt);
    pkt.data = NULL;
    pkt.size = 0;

    while (true)
    {
        ret = avcodec_receive_packet(codec_context, &pkt);
        if (!ret)
        {
            if (pkt.pts != AV_NOPTS_VALUE)
                pkt.pts = av_rescale_q(pkt.pts, codec_context->time_base, video_st->time_base);
            if (pkt.dts != AV_NOPTS_VALUE)
                pkt.dts = av_rescale_q(pkt.dts, codec_context->time_base, video_st->time_base);

            av_write_frame(outctx, &pkt);
            av_packet_unref(&pkt);
        }
        else if (ret == AVERROR(EAGAIN))
        {
            frame->pts = frame_counter++;
            ret = avcodec_send_frame(codec_context, frame);
            if (ret < 0)
                return ERROR_ENCODING_FRAME_SEND;
        }
        else if (ret < 0)
            return ERROR_ENCODING_FRAME_RECEIVE;
        else
            break;
    }

    // This one
    av_frame_free(&frame);
}


  



  Now, this code might have a lot of issues that I'm not aware of, and you are free to point them out if you like. But the line that gives me error is av_frame_free(&frame);.

  



  If I run this in a synthetic test app in c++ that I made, it works. I can even run it in a c# synthetic test app (exactly like the c++ one), and it works. But if I run it though Unity, it crashes on the first frame. The log says "Read from location fe7f8097 caused an access violation.".

  



  I have tried with av_freep() and av_free(). Not sure exactly what makes them different (different example codes use different ones), but none work.

  



  So, what I'm I missing ? The frame is leaking if I don't free it right ? But why does it crash in Unity ?

  



  The whole thing works great in Unity if I don't have the av_frame_free(&frame);. Resulting video looks great !

  



  PS. I'm aware (as far as I know) that the frame also leaks if something fails and returns an error code. But one thing at a time.

  


• avformat_close_input memory leak ?

  20 janvier 2021, par Keen Jackdaw

  I developed an app to push live stream with ffmpeg. When I checked the app with leaks --atExit -- <the app="app"></the> (I'm on mac), I found some memory leak with AVFormatContext.

  


  The minimized code are provided below :

  


  #include <iostream>&#xA;&#xA;extern "C" {&#xA;#include <libavcodec></libavcodec>avcodec.h>&#xA;#include <libavformat></libavformat>avformat.h>&#xA;#include <libavdevice></libavdevice>avdevice.h>&#xA;}&#xA;&#xA;void foo() {&#xA;    avdevice_register_all();&#xA;&#xA;    AVFormatContext *avInputFormatContext = avformat_alloc_context();&#xA;    AVInputFormat *avInputFormat = av_find_input_format("avfoundation");&#xA;    std::cout &lt;&lt; "open input" &lt;&lt; std::endl;&#xA;    int ret = avformat_open_input(&amp;avInputFormatContext, "Capture screen 0", avInputFormat, nullptr);&#xA;    if (ret &lt; 0) { std::cout &lt;&lt; "open input failed: " &lt;&lt; ret &lt;&lt; std::endl; return;}&#xA;&#xA;    avformat_close_input(&amp;avInputFormatContext);&#xA;&#xA;}&#xA;&#xA;int main() {&#xA;    foo();&#xA;    return 0;&#xA;}&#xA;&#xA;</iostream>

  


  The output is

  


  Process:         ffmpegtest [87726]
Path:            /Users/USER/*/ffmpegtest
Load Address:    0x10a752000
Identifier:      ffmpegtest
Version:         ???
Code Type:       X86-64
Platform:        macOS
Parent Process:  leaks [87725]

Date/Time:       2021-01-20 15:44:57.533 +0800
Launch Time:     2021-01-20 15:44:55.760 +0800
OS Version:      macOS 11.1 (20C69)
Report Version:  7
Analysis Tool:   /Applications/Xcode.app/Contents/Developer/usr/bin/leaks
Analysis Tool Version:  Xcode 12.3 (12C33)

Physical footprint:         9.9M
Physical footprint (peak):  10.6M
----

leaks Report Version: 4.0
Process 87726: 14143 nodes malloced for 2638 KB
Process 87726: 1 leak for 32 total leaked bytes.

    1 (32 bytes) ROOT LEAK: 0x7f8c61e1b040 [32]  length: 16  "Capture screen 0"


  


  Did I miss something ?