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• using ffmpeg libavcodec to decode a video file then encode to H264, media file's duration is zero

  1er septembre 2017, par Qing

  Need help, recently, I am using ffmpeg libavcodec to decode a video file then encode to H264 and write to an mp4 media container, finally, the media file’s duration is zero, the following is my code’s workflow：

  AVFormatContext*    input_format_context = NULL;
  
  AVFormatContext*    output_format_context = NULL;
  
  AVIOContext*        output_io_context = NULL;
  
  AVCodecContext*     input_codec_context = NULL;
  
  AVCodecContext*     output_codec_context = NULL;
  
  AVCodec*            codec = NULL;
  
  AVStream*           input_stream = NULL;
  
  AVStream*           output_stream = NULL;
  
  AVFrame*            frame = NULL;
  
  
  
  int convert_init(const char* input_filename, const char* output_filename)
  
  {
  
      /** Allocate a new encode context */
  
      avformat_open_input(&input_format_context, 
  
              input_filename, NULL, NULL); 
  
  
  
      /** Get information on the input file (number of streams etc.). */
  
      avformat_find_stream_info(input_format_context, NULL);  
  
  
  
      /** Open the output file to write to it. */
  
      avio_open(&output_io_context, output_filename, 
  
              AVIO_FLAG_WRITE);
  
  
  
      /** Create a new format context for the output container format. */
  
      output_format_context = avformat_alloc_context();
  
  
  
      /** Associate the output file (pointer) with the container format context. */
  
      output_format_context->pb = output_io_context;
  
  
  
      /** Guess the desired container format based on the file extension. */
  
      output_format_context->oformat = av_guess_format(NULL, 
  
              output_filename, NULL);
  
  
  
      av_strlcpy((output_format_context)->filename, output_filename, 
  
              sizeof(output_format_context->filename));
  
  
  
      /** stream0 is the video stream */
  
      AVStream* input_stream = input_format_context->streams[0];
  
  
  
  
  
      /** 
  
       * Init the input_codec_context 
  
       */
  
  
  
      /** Find a decoder for the audio stream. */
  
      codec = avcodec_find_decoder(input_stream->codecpar->codec_id);
  
  
  
      /** Allocate a new decode context */
  
      input_codec_context = avcodec_alloc_context3(codec);
  
  
  
      /** Initialize the stream parameters with demuxer information */
  
      avcodec_parameters_to_context(input_codec_context, 
  
              input_stream->codecpar);    
  
  
  
      /** Open the decoder for the stream. */
  
      avcodec_open2(input_codec_context, codec, NULL);                                
  
  
  
      /** 
  
       *  Create an output stream for writing encoded data 
  
       *
  
       *  AM I MISSING SOMETHING ?
  
       *
  
       */
  
      output_stream = avformat_new_stream(output_format_context, NULL);
  
  
  
      /** 
  
       * Init the output_codec_context 
  
       */
  
      /** Find a encoder for the output video stream, using H264. */
  
      codec = avcodec_find_encoder(AV_CODEC_ID_H264);     
  
  
  
      /** Allocate an encode context. */
  
      output_codec_context = avcodec_alloc_context3(codec);  
  
  
  
      /** 
  
       *  Setup encode context parameters.
  
       *  
  
       *  AM I MISSING SOMETHING ?
  
       *
  
       * */
  
      output_codec_context->bit_rate = input_codec_context->bit_rate;
  
      output_codec_context->width = input_codec_context->width;
  
      output_codec_context->height = input_codec_context->height;
  
      output_codec_context->time_base = (AVRational){1, 25};
  
      output_codec_context->framerate = (AVRational){25, 1};
  
      output_codec_context->gop_size = 10;
  
      output_codec_context->max_b_frames = 1;
  
      output_codec_context->pix_fmt = AV_PIX_FMT_YUV420P;
  
      output_codec_context->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  
  
  
      /** Setup output_stream codecpar. */
  
      avcodec_parameters_from_context(output_stream->codecpar, 
  
              codec_context);
  
  
  
      /** Alloc an av frame */
  
      frame = av_frame_alloc();           
  
  
  
  }
  
  
  
  void convert_it()
  
  {
  
      AVPacket input_packet;
  
      AVPacket output_packet;
  
  
  
      /** Write the media file container header */
  
      avformat_write_header(output_format_context, NULL);
  
  
  
      /** 
  
       * decode frames and encode to H264 
  
       * */
  
      while (1) { 
  
          av_init_packet(&input_packet);
  
          input_packet.data = NULL;
  
          input_packet.size = 0;
  
  
  
          av_init_packet(&output_packet);
  
          output_packet.data = NULL;
  
          output_packet.size = 0;
  
  
  
          /** Read a frame to decode */
  
          av_read_frame(input_format_context, &input_packet);         
  
          if (av_read_frame is end of file) {
  
              break;
  
          }
  
          ...
  
          ...
  
  
  
          /** Decoding... */
  
          avcodec_send_packet(input_codec_context, &input_packet);
  
          ...
  
          ...
  
  
  
          /** Get a decoded frame */
  
          avcodec_receive_frame(input_codec_context, frame);
  
          ...
  
          ...
  
  
  
          /** Make the frame writable, is it necessary ?? */
  
          av_frame_make_writable(frame);
  
  
  
          /** Encode to H264 */
  
          avcodec_send_frame(output_codec_context, frame);
  
          ...
  
          ...
  
  
  
          /** Get a encoded packet */
  
          avcodec_receive_packet(output_codec_context, &output_packet);
  
  
  
          /** 
  
           * Write the packet to output.  
  
           * Here is the point! should I configure the parameters 
  
           * in packet such as 'pts', 'dts', 'duration', etc, if so, 
  
           * hwo? or I just directory write the packet to output? 
  
           */
  
          av_interleaved_write_frame(output_format_context, &packet);                 
  
      }
  
  
  
      /** Write the media file container trailer */
  
      av_write_trailer(output_format_context);
  
  
  
  }
  
  
  
  int main() {
  
      convert_init("./sample.avi", "./output.mp4");
  
      convert_it();
  
  
  
  }

  using VLC or QuickTime to playback the output.mp4 file, it failed, cause the file duration is zero, when dragging the time progress bar， I can see the picture frame clearly, it seems that the encoding packet buffer data is correct, but the timestamp is error, am I missing something when configure the output_stream ? The following is message from ffprobe.

  ffprobe output.mp4
  
  ffprobe version 3.3.3 Copyright (c) 2007-2017 the FFmpeg developers
  
    built with Apple LLVM version 8.1.0 (clang-802.0.42)
  
    configuration: --enable-shared --enable-libmp3lame
  
    libavutil      55. 58.100 / 55. 58.100
  
    libavcodec     57. 89.100 / 57. 89.100
  
    libavformat    57. 71.100 / 57. 71.100
  
    libavdevice    57.  6.100 / 57.  6.100
  
    libavfilter     6. 82.100 /  6. 82.100
  
    libswscale      4.  6.100 /  4.  6.100
  
    libswresample   2.  7.100 /  2.  7.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf57.71.100
  
    Duration: 00:00:00.06, start: 0.000000, bitrate: 6902181 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 720x408 [SAR 1:1 DAR 30:17], 13929056 kb/s, 90k fps, 90k tbr, 90k tbn, 50 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler

• Getting file info with ffmpeg, object file recognized as Audio ?

  20 décembre 2018, par cpl

  I’m testing a C++ program that should iterate in a directory and find all multimedia files. I used an iteration routine, and for every file I tried using the libav functions to open the file, such as av_find_stream_info in order to find stream info. It works fine for multimedia files, such as video and images, but the problem is that it recognizes some files as audio or video, for example it sees an audio stream inside a .o file ! I also tried to use av_read_frame and it worked fine, without errors ! I would like to avoid filtering by extension, is there any other solution to find "playable" files ?

  Thanks

• ffmpeg command convert a part of video file to an audio file [migrated]

  3 décembre 2013, par Amarnath alias Roobal

  I have a video file (duration 1 hour). I need any part of video file(30 min) to be converted to audio file

  ffmpeg -ss 00:30:00 -t 01:00:00 -i /opt/a.mp4 -vcodec copy -acodec copy /opt/b.mp4

  then i used

  ffmpeg -ss 00:30:00 -t 01:00:00 -i /opt/a.mp4 -acodec copy /opt/b.mp4

  But still I can view the video along with the audio. I need only audio files