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• libavcodec on media entirely in memory

  11 janvier 2019, par Nick

  I’m dealing with small micro videos that exist entirely in memory (as a string). So far, I haven’t been able to get avcodec to properly decode h264 in this way.

  I tried a custom AVIOContext that operates on containerized media :

  struct Stream { char* str; size_t pos; size_t size; };
  
  
  
  static int ReadStream(void* opaque, uint8* buf, int buf_size) {
  
    Stream* strm = reinterpret_cast(opaque);
  
    int read = strm->size-strm->pos;
  
    read = read < buf_size ? read : buf_size;
  
    memcpy(buf, strm->str+sto-æ>pos, read);
  
    memset(buf+read, 0, buf_size-read);
  
    strm->pos += read;
  
    return read;
  
  }
  
  
  
  static int64_t SeekStream(void *opaque, int64_t offset, int whence) {
  
    Stream* strm = reinterpret_cast(opaque);
  
    if (whence == AVSEEK_SIZE) {
  
      return strm->size;
  
    } else if (whence == SEEK_END) {
  
      strm->pos = strm->size;
  
    } else if (whence == SEEK_SET) {
  
      strm->pos = 0;
  
    }
  
    strm->pos += offset;
  
    return strm->pos;
  
  }
  
  
  
  int main(int argc, char *argv[]) {
  
    string content;
  
    GetContents("test.mp4", &content);
  
  
  
    avcodec_register_all();
  
  
  
    uint8* buff = (uint8*)malloc(4096 + AV_INPUT_BUFFER_PADDING_SIZE);
  
    Stream strm = { const_cast(content.data()), 0, content.size() };
  
    void* opaque = reinterpret_cast(&strm);
  
  
  
    AVFormatContext* fmtctx = avformat_alloc_context();
  
    AVIOContext* avctx = avio_alloc_context(buff, 4096, 0, opaque, &ReadStream, nullptr, &SeekStream);
  
    AVInputFormat* ifmt = av_find_input_format("mp4");
  
    AVDictionary* opts = nullptr;
  
  
  
    fmtctx->pb = avctx;
  
    avformat_open_input(&fmtctx, "", ifmt, &opts);
  
    avformat_find_stream_info(fmtctx, &opts);
  
  }

  But that always segfaults at find_stream_info.

  I also tried pre-demuxing the video stream into raw h264 and just sending the stream packets (e.g.) :

  int main(int argc, char *argv[]) {
  
    string content;
  
    GetContents("test.h264", &content);
  
    uint8* data = reinterpret_cast(const_cast(content.c_str()));
  
  
  
    avcodec_register_all();
  
  
  
    AVCodec* codec = avcodec_find_decoder(AV_CODEC_ID_H264);
  
    AVCodecContext* ctx = avcodec_alloc_context3(codec);
  
  
  
    ctx->width = 1080;
  
    ctx->height = 1920;
  
    avcodec_open2(ctx, codec, nullptr);
  
  
  
    AVPacket* pkt = av_packet_alloc();    
  
    AVFrame* frame = av_frame_alloc();
  
  
  
    pkt->data = data;
  
    pkt->size = 4096;
  
    avcodec_send_packet(ctx, pkt);
  
    data += 4096;
  
  }

  But that just gives a nondescript "error while decoding MB # #, bytestream #". Note that I’ve removed the error checking from the allocs, etc. to simplify the code, but I am checking to make sure everything is allocated and instantiated correctly.

  Any suggestions for where my misunderstanding or misuse of avcodec is ?

• Use ffmpeg to assess media quality recursively and output to a file

  6 septembre 2021, par JD71

  Would anyone mind telling me how to use ffmpeg recursively to scan my collection, assess the video quality and export all of the output data to a file ? I've searched quite a bit on the web and there have been some close to what I'm looking for but not exactly. If I should be using something else, I'm open to suggestions as well.

  


  Thank you in advance for any assistance you can provide !

  


  J

  


• Is it possible to create a hls master playlist with .ts chunks ?

  30 mai 2020, par Pallav

  I am trying to create a hls master playlist with .ts chunks(of different playlists) instead of creating it with different variants playlist in nginx using ffmpeg, Can one do that ? if not is there any way I can immediately create the master playlist as soon as nginx receives the first .ts chunk ?

  



  Thanks, your help is much appreciated.