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• Why do I catch the "AccessViolationException" exception in av_hwframe_transfer_data () when I run it as a windows service ?

  5 décembre 2024, par vakym

  I write Windows service witch decodig video stream from camera.
I write it on c# with FFMPEG.Autogen wrapper.

  



  My problem is "AccessViolationException" when i run it as service. 
If i run application as Console Application i have no exceptions.

  



  In Stacktrace i see this :

  



  в FFmpeg.AutoGen.ffmpeg+<>c.<.cctor>b__5_572(FFmpeg.AutoGen.AVFrame*, FFmpeg.AutoGen.AVFrame*, Int32)
в FFmpeg.AutoGen.ffmpeg.av_hwframe_transfer_data(FFmpeg.AutoGen.AVFrame*, FFmpeg.AutoGen.AVFrame*,Int32)
в VideoProviderService.VideoSources.RTSPVideoSource.TryDecodeNextFrame(Boolean ByRef)


  



  Code of TryDecodeNextFrame method :

  



  public IntPtr TryDecodeNextFrame(out bool state)
{
    try
    {
        ffmpeg.av_frame_unref(pFrame);
        ffmpeg.av_frame_unref(cpuFrame);
        int error;
        do
        {
            try
            {
                do
                {
                    timeout = DateTime.Now.AddSeconds(2);
                    error = ffmpeg.av_read_frame(_pFormatContext, pPacket);
                    if (error == ffmpeg.AVERROR_EOF)
                    {
                        state = false;
                        return IntPtr.Zero;
                    }
                    error.ThrowExceptionIfError();
                } while (pPacket->stream_index != _streamIndex);
                ffmpeg.avcodec_send_packet(pCodecContext, pPacket).ThrowExceptionIfError();
            }
            finally
            {
                ffmpeg.av_packet_unref(pPacket);
            }
            error = ffmpeg.avcodec_receive_frame(pCodecContext, pFrame);
        } while (error == ffmpeg.AVERROR(ffmpeg.EAGAIN));
        error.ThrowExceptionIfError();
        ffmpeg.av_hwframe_transfer_data(cpuFrame, pFrame, 0).ThrowExceptionIfError();
        ptrToFrame = (IntPtr)vfc.Convert(*cpuFrame).data[0];  
    }
    catch
    {
        state = false;
        return IntPtr.Zero;
    }
    state = true;
    return ptrToFrame;
}


  



  What i tried to do :

  



  

  1. I checked arguments of av_hwframe_transfer_data.

  


  2. I changed the user for the service.

  


  3. I tried compile as x86 or x64 configuration.

  


  



  I have no idea how to solve this.
Does anyone have any thoughts ?

  


• aacdec_ac : fix signed overflow in ff_aac_ac_update_context()

  22 mai, par Lynne

  aacdec_ac : fix signed overflow in ff_aac_ac_update_context()
  The issue is that state->cur[] is 8-bits, but a+b+1 can overflow
  
  before being clipped to 0xF in the following line, causing an incorrect
  
  state to be saved for the next symbol.
  This solves numerous bitstream desyncs, particularly when coefficients
  
  with magnitude greater than 127 are sent.
  

  • [DH] libavcodec/aac/aacdec_ac.c

• ffmpeg extract segment from video on-the-fly

  29 novembre 2022, par brunoais

  Context

  


  I want to make a service that hosts mp4 files but also provides video streaming.

  


  The server side is made of 2 "small" edge servers with capacity to cache about 0.1% of the content and one main server with a fraction of the bandwidth of the edge servers but much more robust storage.

  


  Recent status

  


  With the help of the ffmpeg manual,
  
Recently, when a segment is requested by an edge server, I run this command in ffmpeg

  


  ffmpeg -i in.mp4 -f hls -hls_list_size 0 -hls_playlist 1 -hls_time 60 -strftime 1  -hls_flags independent_segments+second_level_segment_index+second_level_segment_duration -hls_base_url '/path/to/file/' -hls_segment_filename 'name_%%03d.ts'  -c copy -copyts -hls_segment_type fmp4 out.m3u8


  


  Then obtain the requested segment (plus 3 subsequent ones) then delete everything.

  


  Current status

  


  Currently, I tried to get some level of optimization using -to :

  


  ffmpeg -i in.mp4 -to  -f hls -hls_list_size 0 -hls_playlist 1 -hls_time 60 -strftime 1  -hls_flags independent_segments+second_level_segment_index+second_level_segment_duration -hls_base_url '/path/to/file/' -hls_segment_filename 'name_%%03d.ts'  -c copy -copyts -hls_segment_type fmp4 out.m3u8


  


  Then sending the requested segments to the edge that requested them, then delete the result.
Do note that /path/to/file/ is a tmpfs with quite modest capacity (files can't stay there for too long).

  


  The current setback

  


  The main issue I get with the current process is that it takes a long time to obtain the last segments (2-4s).
That creates a bottleneck in how long segments take to be served. I can increase the buffer from 3 videos to 5 (or even more) but that doesn't solve the actual problem and, instead, will bring more strain on other areas.

  


  Cutting is not reliable

  


  There doesn't seem to exist an option to select what segments to generate using ffmpeg.

  


  Using cutting argument for start time (-ss) has shown to usually work but regularely causes the first keyframe used to be wrong. However, I believe I have all segment files in variable length and cut at the keyframe of the original file.

  


  Help needed

  


  How to extract an arbitrary segment of an mp4, described in the m3u8 file (which was done in a previous extraction) ?

  


  I have full control over ffmpeg and I can automate edits to the m3u8 file after generating them, as required. However, I need to understand and see how can this be solved.