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  • SegFault while freeing nvenc hwdevice_ctx

    23 février 2024, par camelCase

    For a project, I created a class encoding the output of an OpenGL renderbuffer object using h264_nvenc. Unfortunately, tidying up doesn't work, and the program crashes with a SegFault. The reason is accessing an unaccessable memory region, happening twice in the final lines (see below) when calling av_buffer_unref( &_hwDeviceRefCtx ) and implicitely also during avcodec_free_context( &_pCodecCtx ), but both calls are required for shutting down.

    


    The (in this case relevant) valgrind-output is

    


    Invalid read of size 8
   at 0x48AD987: UnknownInlinedFun (buffer.c:121)
   by 0x48AD987: UnknownInlinedFun (buffer.c:144)
   by 0x48AD987: av_buffer_unref (buffer.c:139)
   by 0x5D06D7A: avcodec_close (avcodec.c:486)
   by 0x628DD7D: avcodec_free_context (options.c:175)
   by 0x10A863: main (main.cpp:115)
 Address 0x17812700 is 0 bytes inside a block of size 24 free'd
   at 0x484488F: free (vg_replace_malloc.c:985)
   by 0x48AD98F: UnknownInlinedFun (buffer.c:127)
   by 0x48AD98F: UnknownInlinedFun (buffer.c:144)
   by 0x48AD98F: av_buffer_unref (buffer.c:139)
   by 0x48BE098: hwframe_ctx_free (hwcontext.c:240)
   by 0x48AD9A6: UnknownInlinedFun (buffer.c:133)
   by 0x48AD9A6: UnknownInlinedFun (buffer.c:144)
   by 0x48AD9A6: av_buffer_unref (buffer.c:139)
   by 0x5D06D0A: UnknownInlinedFun (decode.c:1261)
   by 0x5D06D0A: avcodec_close (avcodec.c:465)
   by 0x628DD7D: avcodec_free_context (options.c:175)
   by 0x10A863: main (main.cpp:115)
 Block was alloc'd at
   at 0x4849366: posix_memalign (vg_replace_malloc.c:2099)
   by 0x48D9BD5: av_malloc (mem.c:105)
   by 0x48D9DAD: av_mallocz (mem.c:256)
   by 0x48AD8DD: UnknownInlinedFun (buffer.c:44)
   by 0x48AD8DD: av_buffer_create (buffer.c:64)
   by 0x48BDDEB: av_hwdevice_ctx_alloc (hwcontext.c:179)
   by 0x48BDF29: av_hwdevice_ctx_create (hwcontext.c:622)
   by 0x10A482: main (main.cpp:43)

Invalid free() / delete / delete[] / realloc()
   at 0x484488F: free (vg_replace_malloc.c:985)
   by 0x48AD98F: UnknownInlinedFun (buffer.c:127)
   by 0x48AD98F: UnknownInlinedFun (buffer.c:144)
   by 0x48AD98F: av_buffer_unref (buffer.c:139)
   by 0x5D06D7A: avcodec_close (avcodec.c:486)
   by 0x628DD7D: avcodec_free_context (options.c:175)
   by 0x10A863: main (main.cpp:115)
 Address 0x17812700 is 0 bytes inside a block of size 24 free'd
   at 0x484488F: free (vg_replace_malloc.c:985)
   by 0x48AD98F: UnknownInlinedFun (buffer.c:127)
   by 0x48AD98F: UnknownInlinedFun (buffer.c:144)
   by 0x48AD98F: av_buffer_unref (buffer.c:139)
   by 0x48BE098: hwframe_ctx_free (hwcontext.c:240)
   by 0x48AD9A6: UnknownInlinedFun (buffer.c:133)
   by 0x48AD9A6: UnknownInlinedFun (buffer.c:144)
   by 0x48AD9A6: av_buffer_unref (buffer.c:139)
   by 0x5D06D0A: UnknownInlinedFun (decode.c:1261)
   by 0x5D06D0A: avcodec_close (avcodec.c:465)
   by 0x628DD7D: avcodec_free_context (options.c:175)
   by 0x10A863: main (main.cpp:115)
 Block was alloc'd at
   at 0x4849366: posix_memalign (vg_replace_malloc.c:2099)
   by 0x48D9BD5: av_malloc (mem.c:105)
   by 0x48D9DAD: av_mallocz (mem.c:256)
   by 0x48AD8DD: UnknownInlinedFun (buffer.c:44)
   by 0x48AD8DD: av_buffer_create (buffer.c:64)
   by 0x48BDDEB: av_hwdevice_ctx_alloc (hwcontext.c:179)
   by 0x48BDF29: av_hwdevice_ctx_create (hwcontext.c:622)
   by 0x10A482: main (main.cpp:43)


    


    that is also duplicated (due to the calls to avcodec_free_context() and av_buffer_unref()).

    


    The question is : How can I fix this ?

    


    The (more or less) minimal (not) working example reads

    


    #include <string>&#xA;&#xA;extern "C" {&#xA;  #include <libavutil></libavutil>opt.h>&#xA;  #include <libavcodec></libavcodec>avcodec.h>&#xA;  #include <libavformat></libavformat>avformat.h>&#xA;  #include <libavutil></libavutil>hwcontext.h>&#xA;  #include <libavutil></libavutil>pixdesc.h>&#xA;  #include <libavutil></libavutil>hwcontext_cuda.h>&#xA;}&#xA;&#xA;//(former) libx264 encoding based on https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/muxing.c&#xA;//update to h264_nvenc with a lot of help from https://stackoverflow.com/questions/49862610/opengl-to-ffmpeg-encode&#xA;//and some additional info of https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/vaapi_encode.c&#xA;&#xA;int main() {&#xA;    const int _SrcImageWidth=640;&#xA;    const int _SrcImageHeight=480;&#xA;    &#xA;    const AVOutputFormat *_oFmt = nullptr;&#xA;    AVFormatContext *_oFmtCtx = nullptr;&#xA;    &#xA;    const AVCodec *_pCodec = nullptr;&#xA;    AVCodecContext *_pCodecCtx = nullptr;&#xA;    &#xA;    AVFrame* _frame;&#xA;    AVPacket* _packet;&#xA;    AVStream* _stream;&#xA;    &#xA;    AVBufferRef *_hwDeviceRefCtx = nullptr;&#xA;    const CUcontext* _cudaCtx;&#xA;    &#xA;    const std::string _OutFileName = "output.mkv";&#xA;    &#xA;    //constructor part&#xA;    int ret;&#xA;&#xA;    //output format context      &#xA;    avformat_alloc_output_context2( &amp;_oFmtCtx, nullptr, nullptr, _OutFileName.c_str() );&#xA;    _oFmt = _oFmtCtx->oformat;&#xA;&#xA;    //hardware format context&#xA;    ret = av_hwdevice_ctx_create( &amp;_hwDeviceRefCtx, AV_HWDEVICE_TYPE_CUDA, "NVIDIA GeForce RTX 4070", nullptr, 0 );&#xA;&#xA;    //hardware frame context for device buffer allocation&#xA;    AVBufferRef* hwFrameRefCtx = av_hwframe_ctx_alloc( _hwDeviceRefCtx );&#xA;    AVHWFramesContext* hwFrameCtx = (AVHWFramesContext*) (hwFrameRefCtx->data);&#xA;    hwFrameCtx->width = _SrcImageWidth;&#xA;    hwFrameCtx->height = _SrcImageHeight;&#xA;    hwFrameCtx->sw_format = AV_PIX_FMT_0BGR32;&#xA;    hwFrameCtx->format = AV_PIX_FMT_CUDA;&#xA;    hwFrameCtx->device_ref = _hwDeviceRefCtx;&#xA;    hwFrameCtx->device_ctx = (AVHWDeviceContext*) _hwDeviceRefCtx->data;&#xA;&#xA;    ret = av_hwframe_ctx_init( hwFrameRefCtx );&#xA;&#xA;    //get cuda context&#xA;    const AVHWDeviceContext* hwDeviceCtx = (AVHWDeviceContext*)(_hwDeviceRefCtx->data);&#xA;    const AVCUDADeviceContext* cudaDeviceCtx = (AVCUDADeviceContext*)(hwDeviceCtx->hwctx);&#xA;    _cudaCtx = &amp;(cudaDeviceCtx->cuda_ctx);&#xA;&#xA;    //codec context&#xA;    _pCodec = avcodec_find_encoder_by_name( "h264_nvenc" );&#xA;&#xA;    _packet = av_packet_alloc();&#xA;&#xA;    _stream = avformat_new_stream( _oFmtCtx, nullptr );&#xA;    _stream->id = _oFmtCtx->nb_streams - 1;&#xA;    _pCodecCtx = avcodec_alloc_context3( _pCodec );&#xA;&#xA;    _pCodecCtx->qmin = 18;&#xA;    _pCodecCtx->qmax = 20;&#xA;    _pCodecCtx->width = _SrcImageWidth;&#xA;    _pCodecCtx->height = _SrcImageHeight;&#xA;    _pCodecCtx->framerate = (AVRational) {25,1};&#xA;    _pCodecCtx->time_base = (AVRational) {1,25};&#xA;    _stream->time_base = _pCodecCtx->time_base;&#xA;    _pCodecCtx->gop_size = 12; //I-Frame every at most 12 frames&#xA;    _pCodecCtx->max_b_frames = 2;&#xA;    _pCodecCtx->pix_fmt = AV_PIX_FMT_CUDA; //required to use renderbuffer as src&#xA;    _pCodecCtx->codec_type = AVMEDIA_TYPE_VIDEO;&#xA;    _pCodecCtx->sw_pix_fmt = AV_PIX_FMT_0BGR32; &#xA;    _pCodecCtx->hw_device_ctx = _hwDeviceRefCtx;&#xA;    _pCodecCtx->hw_frames_ctx = av_buffer_ref( hwFrameRefCtx );&#xA;    av_opt_set(_pCodecCtx->priv_data, "preset", "p7", 0);&#xA;    av_opt_set(_pCodecCtx->priv_data, "rc", "vbr", 0);&#xA;    if( _oFmtCtx->oformat->flags &amp; AVFMT_GLOBALHEADER ) {&#xA;        _pCodecCtx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;&#xA;    }&#xA;&#xA;    ret = avcodec_open2( _pCodecCtx, _pCodec, nullptr );&#xA;    avcodec_parameters_from_context( _stream->codecpar, _pCodecCtx );&#xA;&#xA;    if (!(_oFmtCtx->oformat->flags &amp; AVFMT_NOFILE)) {&#xA;        ret = avio_open(&amp;_oFmtCtx->pb, _OutFileName.c_str(), AVIO_FLAG_WRITE);&#xA;    }&#xA;    ret = avformat_write_header( _oFmtCtx, nullptr );&#xA;&#xA;    //use hardware frame from above&#xA;    _frame = av_frame_alloc();&#xA;    ret = av_hwframe_get_buffer( _pCodecCtx->hw_frames_ctx, _frame, 0 );&#xA;    _frame->pts = 1;&#xA;&#xA;    av_buffer_unref( &amp;hwFrameRefCtx );&#xA;&#xA;    //destructor part&#xA;    av_frame_free( &amp;_frame );&#xA;    av_packet_free( &amp;_packet );&#xA;&#xA;    av_write_trailer( _oFmtCtx );&#xA;    avio_closep( &amp;_oFmtCtx->pb );&#xA;&#xA;    avformat_free_context( _oFmtCtx );&#xA;&#xA;    avcodec_free_context( &amp;_pCodecCtx );&#xA;    av_buffer_unref( &amp;_hwDeviceRefCtx );&#xA;&#xA;    return 0;&#xA;}&#xA;</string>

    &#xA;

    and compiles with (linux user)

    &#xA;

    g&#x2B;&#x2B; -lavutil -lavformat -lavcodec -lz -lavutil -lswscale -lswresample -lm -ggdb3 -I/opt/cuda/include main.cpp&#xA;

    &#xA;

    Thanks in advance !

    &#xA;

  • I want to take any Audio from a file and encode it as PCM_ALAW. My Example is a .m4a file to .wav file

    22 novembre 2023, par Clockman

    I have been working on this for a while now while am generally new to ffmpeg library, I have studied it a bit. The challenge I have that at the point of witting to file I get the following exception.

    &#xA;

    "Exception thrown at 0x00007FFACA8305B3 (avformat-60.dll) in FfmpegPractice.exe : 0xC0000005 : Access violation writing location 0x0000000000000000.". I understand this means am writing to an uninitialized buffer am unable to discover why this is happening. The exception call stack shows the following

    &#xA;

    avformat-60.dll!avformat_write_header() C&#xA;avformat-60.dll!ff_write_chained()  C&#xA;avformat-60.dll!ff_write_chained()  C&#xA;avformat-60.dll!av_write_frame()    C&#xA;FfmpegPractice.exe!main() Line 215  C&#x2B;&#x2B;&#xA;

    &#xA;

    Some things I have tried

    &#xA;

    This code is part of a larger project built with CMake but for some reason I could no step into ffmpeg library while debugging, So I recompiled ffmpeg ensured debugging was enabled so I could drill down to the root cause but I still could not step into the ffmpeg library.

    &#xA;

    I then created a minimal project using visual studio c++ console project and I still could not step into the code.

    &#xA;

    I have read through many ffmpeg docs and some I could find on the internet and I still could not solve it.

    &#xA;

    This is the code

    &#xA;

    #include <iostream>&#xA;&#xA;extern "C" {&#xA;#include <libavcodec></libavcodec>avcodec.h>&#xA;#include <libavformat></libavformat>avformat.h>&#xA;#include <libswresample></libswresample>swresample.h>&#xA;#include <libavutil></libavutil>opt.h>&#xA;#include <libavutil></libavutil>audio_fifo.h>&#xA;}&#xA;&#xA;using namespace std;&#xA;&#xA;//in audio file&#xA;string filename{ "rapid_caller_test.m4a" };&#xA;AVFormatContext* pFormatCtx{};&#xA;AVCodecContext* pCodecCtx{};&#xA;AVStream* pStream{};&#xA;&#xA;//out audio file&#xA;string outFilename{ "output.wav" };&#xA;AVFormatContext* pOutFormatCtx{ nullptr };&#xA;AVCodecContext* pOutCodecCtx{ nullptr };&#xA;AVIOContext* pOutIoContext{ nullptr };&#xA;const AVCodec* pOutCodec{ nullptr };&#xA;AVStream* pOutStream{ nullptr };&#xA;const int OUTPUT_CHANNELS = 1;&#xA;const int SAMPLE_RATE = 8000;&#xA;const int OUT_BIT_RATE = 64000;&#xA;uint8_t** convertedSamplesBuffer{ nullptr };&#xA;int64_t dstNmbrSamples{ 0 };&#xA;int dstLineSize{ 0 };&#xA;static int64_t pts{ 0 };&#xA;&#xA;//conversion context;&#xA;SwrContext* swr{};&#xA;&#xA;uint32_t i{ 0 };&#xA;int audiostream{ -1 };&#xA;&#xA;&#xA;void cleanUp() &#xA;{&#xA;  avcodec_free_context(&amp;pOutCodecCtx);;&#xA;  avio_closep(&amp;(pOutFormatCtx)->pb);&#xA;  avformat_free_context(pOutFormatCtx);&#xA;  pOutFormatCtx = nullptr;&#xA;}&#xA;&#xA;int main()&#xA;{&#xA;&#xA;/*&#xA;* section to setup input file&#xA;*/&#xA;if (avformat_open_input(&amp;pFormatCtx, filename.data(), nullptr, nullptr) != 0) {&#xA;  cout &lt;&lt; "could not open file " &lt;&lt; filename &lt;&lt; endl;&#xA;  return -1;&#xA;}&#xA;if (avformat_find_stream_info(pFormatCtx, nullptr) &lt; 0) {&#xA;  cout &lt;&lt; "Could not retrieve stream information from file " &lt;&lt; filename &lt;&lt; endl;&#xA;  return -1;&#xA;}&#xA;av_dump_format(pFormatCtx, 0, filename.c_str(), 0);&#xA;&#xA;for (i = 0; i &lt; pFormatCtx->nb_streams; i&#x2B;&#x2B;) {&#xA;  if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {&#xA;    audiostream = i;&#xA;    break;&#xA;  }&#xA;}&#xA;if (audiostream == -1) {&#xA;  cout &lt;&lt; "did not find audio stream" &lt;&lt; endl;&#xA;  return -1;&#xA;}&#xA;&#xA;pStream = pFormatCtx->streams[audiostream];&#xA;const AVCodec* pCodec{ avcodec_find_decoder(pStream->codecpar->codec_id) };&#xA;pCodecCtx = avcodec_alloc_context3(pCodec);&#xA;avcodec_parameters_to_context(pCodecCtx, pStream->codecpar);&#xA;if (avcodec_open2(pCodecCtx, pCodec, nullptr)) {&#xA;  cout &lt;&lt; "could not open codec" &lt;&lt; endl;&#xA;  return -1;&#xA;}&#xA;&#xA;/*&#xA;* section to set up output file which is a G711 audio&#xA;*/&#xA;if (avio_open(&amp;pOutIoContext, outFilename.data(), AVIO_FLAG_WRITE)) {&#xA;  cout &lt;&lt; "could not open out put file" &lt;&lt; endl;&#xA;  return -1;&#xA;}&#xA;if (!(pOutFormatCtx = avformat_alloc_context())) {&#xA;  cout &lt;&lt; "could not create format conext" &lt;&lt; endl;&#xA;  cleanUp();&#xA;  return -1;&#xA;}&#xA;pOutFormatCtx->pb = pOutIoContext;&#xA;if (!(pOutFormatCtx->oformat = av_guess_format(nullptr, outFilename.data(), nullptr))) {&#xA;  cout &lt;&lt; "could not find output file format" &lt;&lt; endl;&#xA;  cleanUp();&#xA;  return -1;&#xA;}&#xA;if (!(pOutFormatCtx->url = av_strdup(outFilename.data()))) {&#xA;  cout &lt;&lt; "could not allocate file name" &lt;&lt; endl;&#xA;  cleanUp();&#xA;  return -1;&#xA;}&#xA;if (!(pOutCodec = avcodec_find_encoder(AV_CODEC_ID_PCM_ALAW))) {&#xA;  cout &lt;&lt; "codec not found" &lt;&lt; endl;&#xA;  cleanUp();&#xA;  return -1;&#xA;}&#xA;if (!(pOutStream = avformat_new_stream(pOutFormatCtx, nullptr))) {&#xA;  cout &lt;&lt; "could not create new stream" &lt;&lt; endl;&#xA;  cleanUp();&#xA;  return -1;&#xA;}&#xA;if (!(pOutCodecCtx = avcodec_alloc_context3(pOutCodec))) {&#xA;  cout &lt;&lt; "could not allocate codec context" &lt;&lt; endl;&#xA;  return -1;&#xA;}&#xA;av_channel_layout_default(&amp;pOutCodecCtx->ch_layout, OUTPUT_CHANNELS);&#xA;pOutCodecCtx->sample_rate = SAMPLE_RATE;&#xA;pOutCodecCtx->sample_fmt = pOutCodec->sample_fmts[0];&#xA;pOutCodecCtx->bit_rate = OUT_BIT_RATE;&#xA;&#xA;//setting sample rate for the container&#xA;pOutStream->time_base.den = SAMPLE_RATE;&#xA;pOutStream->time_base.num = 1;&#xA;if (pOutFormatCtx->oformat->flags &amp; AVFMT_GLOBALHEADER)&#xA;  pOutCodecCtx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;&#xA;&#xA;if (avcodec_open2(pOutCodecCtx, pOutCodec, nullptr)) {&#xA;  cout &lt;&lt; "could not open output codec" &lt;&lt; endl;&#xA;  cleanUp();&#xA;  return -1;&#xA;}&#xA;if ((avcodec_parameters_from_context(pOutStream->codecpar, pOutCodecCtx)) &lt; 0) {&#xA;  cout &lt;&lt; "could not initialize stream parameters" &lt;&lt; endl;&#xA;}   &#xA;&#xA;AVPacket* packet = av_packet_alloc();&#xA;&#xA;swr = swr_alloc();&#xA;swr_alloc_set_opts2(&amp;swr, &amp;pOutCodecCtx->ch_layout, pOutCodecCtx->sample_fmt, pOutCodecCtx->sample_rate,&amp;pCodecCtx->ch_layout, pCodecCtx->sample_fmt, pCodecCtx->sample_rate, 0, nullptr);&#xA;swr_init(swr);&#xA;&#xA;int ret{};&#xA;int bSize{};&#xA;while (av_read_frame(pFormatCtx, packet) >= 0) {&#xA;  AVFrame* pFrame = av_frame_alloc();&#xA;  AVFrame* pOutFrame = av_frame_alloc();&#xA;  if (packet->stream_index == audiostream) {&#xA;    ret = avcodec_send_packet(pCodecCtx, packet);&#xA;    while (ret >= 0) {&#xA;    ret = avcodec_receive_frame(pCodecCtx, pFrame);&#xA;    if (ret == AVERROR(EAGAIN))&#xA;    continue;&#xA;    else if (ret == AVERROR_EOF)&#xA;    break;&#xA;    dstNmbrSamples = av_rescale_rnd(swr_get_delay(swr, pCodecCtx->sample_rate) &#x2B; pFrame->nb_samples, pOutCodecCtx->sample_rate, pCodecCtx->sample_rate, AV_ROUND_UP);&#xA;    if ((av_samples_alloc_array_and_samples(&amp;convertedSamplesBuffer, &amp;dstLineSize, pOutCodecCtx->ch_layout.nb_channels,dstNmbrSamples, pOutCodecCtx->sample_fmt, 0)) &lt; 0) {&#xA;    cout &lt;&lt; "coult not allocate samples array and buffer" &lt;&lt; endl;&#xA;    }&#xA;    int channel_samples_count{ 0 };&#xA;    channel_samples_count = swr_convert(swr, convertedSamplesBuffer, dstNmbrSamples, (const uint8_t**)pFrame->data, pFrame->nb_samples);&#xA;    bSize = av_samples_get_buffer_size(&amp;dstLineSize, pOutCodecCtx->ch_layout.nb_channels, channel_samples_count, pOutCodecCtx->sample_fmt, 0);&#xA;    cout &lt;&lt; "no of samples is " &lt;&lt; channel_samples_count &lt;&lt; " the buffer size " &lt;&lt; bSize &lt;&lt; endl;&#xA;    pOutFrame->nb_samples = channel_samples_count;&#xA;    av_channel_layout_copy(&amp;pOutFrame->ch_layout, &amp;pOutCodecCtx->ch_layout);&#xA;    pOutFrame->format = pOutCodecCtx->sample_fmt;&#xA;    pOutFrame->sample_rate = pOutCodecCtx->sample_rate;&#xA;    if ((av_frame_get_buffer(pOutFrame, 0)) &lt; 0) {&#xA;    cout &lt;&lt; "could not allocate output frame samples " &lt;&lt; endl;&#xA;    av_frame_free(&amp;pOutFrame);&#xA;  }&#xA;                &#xA;    //populate out frame buffer&#xA;    av_frame_make_writable(pOutFrame);&#xA;    for (int i{ 0 }; i &lt; bSize; i&#x2B;&#x2B;) {&#xA;    pOutFrame->data[0][i] = convertedSamplesBuffer[0][i];&#xA;    cout &lt;&lt; pOutFrame->data[0][i];&#xA;   }&#xA;   if (pOutFrame) {&#xA;   pOutFrame->pts = pts;&#xA;   pts &#x2B;= pOutFrame->nb_samples;&#xA;  }&#xA;   int res = avcodec_send_frame(pOutCodecCtx, pOutFrame);&#xA;    if (res &lt; 0) {&#xA;    cout &lt;&lt; "error sending frame to encoder" &lt;&lt; endl;&#xA;    cleanUp();&#xA;    return -1;&#xA;   }&#xA;   //int er = avformat_write_header(pOutFormatCtx,nullptr);&#xA;   AVPacket* pOutPacket = av_packet_alloc();&#xA;   pOutPacket->time_base.num = 1;&#xA;   pOutPacket->time_base.den = 8000;&#xA;   if (pOutPacket == nullptr) {&#xA;    cout &lt;&lt; "unable to allocate packet" &lt;&lt; endl;&#xA;  }&#xA;  while (res >= 0) {&#xA;   res = avcodec_receive_packet(pOutCodecCtx, pOutPacket);&#xA;   if (res == AVERROR(EAGAIN))&#xA;    continue;&#xA;   else if (ret == AVERROR_EOF)&#xA;    break;&#xA;   av_packet_rescale_ts(pOutPacket, pOutCodecCtx->time_base, pOutFormatCtx->streams[0]->time_base);&#xA;   //av_dump_format(pOutFormatCtx, 0, outFilename.c_str(), 1);&#xA;   if (av_write_frame(pOutFormatCtx, pOutPacket) &lt; 0) {&#xA;    cout &lt;&lt; "could not write frame" &lt;&lt; endl;&#xA;    }&#xA;   }&#xA;  }&#xA;}&#xA; av_frame_free(&amp;pFrame);&#xA; av_frame_free(&amp;pOutFrame);&#xA;}&#xA;if (av_write_trailer(pOutFormatCtx) &lt; 0) {&#xA; cout &lt;&lt; "could not write file trailer" &lt;&lt; endl;&#xA;}&#xA;swr_free(&amp;swr);&#xA;avcodec_free_context(&amp;pOutCodecCtx);&#xA;av_packet_free(&amp;packet);&#xA;}&#xA;</iostream>

    &#xA;

    Error/Exception

    &#xA;

    The exception is thrown when I call

    &#xA;

    if (av_write_frame(pOutFormatCtx, pOutPacket) &lt; 0)  {   cout &lt;&lt; "could not write frame" &lt;&lt; endl; } &#xA;I also called this line

    &#xA;

    //int er = avformat_write_header(pOutFormatCtx,nullptr);

    &#xA;

    to see if I will get an exception but it did not throw any exception.

    &#xA;

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  • How to Conduct a Customer Journey Analysis (Step-by-Step)

    9 mai 2024, par Erin

    Your customers are everything.

    Treat them right, and you can generate recurring revenue for years. Treat them wrong ; you’ll be spinning your wheels and dealing with churn.

    How do you give your customers the best experience possible so they want to stick around ?

    Improve their customer experience.

    How ?

    By conducting a customer journey analysis.

    When you know how your customers experience your business, you can improve it to meet and exceed customer expectations.

    In this guide, we’ll break down how the customer journey works and give you a step-by-step guide to conduct a thorough customer journey analysis so you can grow your brand.

    What is a customer journey analysis ?

    Every customer you’ve ever served went on a journey to find you.

    From the moment they first heard of you, to the point that they became a customer. 

    Everything in between is the customer journey.

    A customer journey analysis is how you track and analyse how your customers use different channels to interact with your brand.

    What is a customer journey analysis?

    Analysing your customer journey involves identifying the customer’s different touchpoints with your business so you can understand how it impacts their experience. 

    This means looking at every moment they interacted with your brand before, during and after a sale to help you gain actionable insights into their experience and improve it to reach your business objectives.

    Your customers go through specific customer touchpoints you can track. By analysing this customer journey from a bird’s eye view, you can get a clear picture of the entire customer experience.

    4 benefits of customer journey analysis

    Before we dive into the different steps involved in a customer journey analysis, let’s talk about why it’s vital to analyse the customer journey.

    By regularly analysing your customer journey, you’ll be able to improve the entire customer experience with practical insights, allowing you to :

    Understand your customers better

    What’s one key trait all successful businesses have ?

    They understand their customers.

    By analysing your customer journey regularly, you’ll gain new insights into their wants, needs, desires and behaviours, allowing you to serve them better. These insights will show you what led them to buy a product (or not).

    For example, through conducting a customer journey analysis, a company might find out that customers who come from LinkedIn are more likely to buy than those coming from Facebook.

    Find flaws in your customer journey

    Nobody wants to hear they have flaws. But the reality is your customer journey likely has a few flaws you could improve.

    By conducting customer journey analysis consistently, you’ll be able to pinpoint precisely where you’re losing prospects along the way. 

    For example, you may discover you’re losing customers through Facebook Ads. Or you may find your email strategy isn’t as good as it used to be.

    But it’s not just about the channel. It could be a transition between two channels. For example, you may have great engagement on Instagram but are not converting them into email subscribers. The issue may be that your transition between the two channels has a leak.

    Or you may find that prospects using certain devices (i.e., mobile, tablet, desktop) have lower conversions. This might be due to design and formatting issues across different devices.

    By looking closely at your customer journey and the different customer touchpoints, you’ll see issues preventing prospects from turning into leads or customers from returning to buy again as loyal customers.

    Gain insights into how you can improve your brand

    Your customer journey analysis won’t leave you with a list of problems. Instead, you’ll have a list of opportunities.

    Since you’ll be able to better understand your customers and where they’re falling off the sales funnel, you’ll have new insights into how you can improve the experience and grow your brand.

    For example, maybe you notice that your visitors are getting stuck at one stage of the customer journey and you’re trying to find out why.

    So, you leverage Matomo’s heatmaps, sessions recordings and scroll depth to find out more.

    In the case below, we can see that Matomo’s scroll map is showing that only 65% of the visitors are reaching the main call to action (to write a review). 

    Scroll depth screenshot in Matomo displaying lack of clicks to CTA button

    To try to push for higher conversions and get more reviews, we could consider moving that button higher up on the page, ideally above the fold.

    Rather than guessing what’s preventing conversions, you can use user behaviour analytics to “step in our user’s shoes” so you can optimise faster and with confidence.

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    Grow your revenue

    By taking charge of your customer journey, you can implement different strategies that will help you increase your reach, gain more prospects, convert more prospects into customers and turn regulars into loyal customers.

    Using customer journey analysis will help you optimise those different touchpoints to maximise the ROI of your channels and get the most out of each marketing activity you implement.

    7 steps to conduct a customer journey analysis

    Now that you know the importance of conducting a customer journey analysis regularly, let’s dive into how to implement an analysis.

    Here are the seven steps you can take to analyse the customer journey to improve your customer experience :

    7 steps to conduct a customer journey analysis.

    1. Map out your customer journey

    Your first step to conducting an effective customer journey analysis is to map your entire customer journey.

    Customer journey mapping means looking at several factors :

    • Buying process
    • Customer actions
    • Buying emotions
    • Buying pain points
    • Solutions

    Once you have an overview of your customer journey maps, you’ll gain insights into your customers, their interests and how they interact with your brand. 

    After this, it’s time to dive into the touchpoints.

    2. Identify all the customer touchpoints 

    To improve your customer journey, you need to know every touchpoint a customer can (and does) make with your brand.

    This means taking note of every single channel and medium they use to communicate with your brand :

    • Website
    • Social media
    • Search engines (SEO)
    • Email marketing
    • Paid advertising
    • And more

    Essentially, anywhere you communicate and interact with your customers is fair game to analyse.

    If you want to analyse your entire sales funnel, you can try Matomo, a privacy-friendly web analytics tool. 

    You should make sure to split up your touchpoints into different customer journey stages :

    • Awareness
    • Consideration
    • Conversion
    • Advocacy

    Then, it’s time to move on to how customers interact on these channels.

    Try Matomo for Free

    Get the web insights you need, without compromising data accuracy.

    No credit card required

    3. Measure how customers interact on each channel

    To understand the customer journey, you can’t just know where your customers interact with you. You end up learning how they’re interacting.

    This is only possible by measuring customer interactions.

    How ?

    By using a web analytics tool like Matomo.

    With Matomo, you can track every customer action on your website.

    This means anytime they :

    • Visit your website
    • View a web page
    • Click a link
    • Fill out a form
    • Purchase a product
    • View different media
    • And more

    You should analyse your engagement on your website, apps and other channels, like email and social media.

    4. Implement marketing attribution

    Now that you know where your customers are and how they interact, it’s time to analyse the effectiveness of each channel based on your conversion rates.

    Implementing marketing attribution (or multi-touch attribution) is a great way to do this.

    Attribution is how you determine which channels led to a conversion.

    While single-touch attribution models credit one channel for a conversion, marketing attribution gives credit to a few channels.

    For example, let’s say Bob is looking for a new bank. He sees an Instagram post and finds himself on HSBC’s website. After looking at a few web pages, he attends a webinar hosted by HSBC on financial planning and investment strategies. One week later, he gets an email from HSBC following up on the webinar. Then, he decides to sign up for HSBC’s online banking.

    Single touch attribution would attribute 100% of the conversion to email, which doesn’t show the whole picture. Marketing attribution would credit all channels : social media, website content, webinars and email.

    Matomo offers multiple attribution models. These models leverage different weighting factors, like time decay or linear, so that you can allocate credit to each touchpoint based on its impact.

    Matomo’s multi-touch attribution reports give you in-depth insights into how revenue is distributed across different channels. These detailed reports help you analyse each channel’s contribution to revenue generation so you can optimise the customer journey and improve business outcomes.

    Try Matomo for Free

    Get the web insights you need, without compromising data accuracy.

    No credit card required

    5. Use a funnels report to find where visitors are leaving

    Once you set up your marketing attribution, it’s time to analyse where visitors are falling off.

    You can leverage Matomo funnels to find out the conversion rate at each step of the journey on your website. Funnel reports can help you see exactly where visitors are falling through the cracks so you can increase conversions.

    6. Analyse why visitors aren’t converting

    Once you can see where visitors are leaving, you can start to understand why.

    For example, let’s say you analyse your funnels report in Matomo and see your landing page is experiencing the highest level of drop-offs.

    Screenshot of Forms Overview report in Matomo's Form Analytics feature

    You can also use form analytics to find out why users aren’t converting on your landing pages – a crucial part of the customer journey.

    7. A/B test to improve the customer journey

    The final step to improve your customer journey is to conduct A/B tests. These are tests where you test one version of a landing page to see which one converts better, drives more traffic, or generates more revenue.

    For example, you could create two versions of a header on your website and drive 50% of your traffic to each version. Then, once you’ve got your winner, you can keep that as your new landing page.

    Screenshot of A/B testing report in Matomo

    Using the data from your A/B tests, you can optimise your customer journey to help convert more prospects into customers.

    Use Matomo to improve your customer journey analysis

    Now that you understand why it’s important to conduct customer journey analysis regularly and how it works, it’s time to put this into practice.

    To improve the customer journey, you need to understand what’s happening at each stage of your funnel. 

    Matomo gives you insights into your customer journey so you can improve website performance and convert more visitors into customers.

    Used by over 1 million websites, Matomo is the leading privacy-friendly web analytics solution in the world. 

    Matomo provides you with accurate, unsampled data so you understand exactly what’s going on with your website performance.

    The best part ?

    It’s easy to use and is compliant with the strictest privacy regulations.

    Try Matomo free for 21-days and start Improving your customer journey. No credit card required.