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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

• Is it possible to set channel layout of wave file using ffmpeg without re-encoding the file ?

  27 août 2020, par John Baker

  I want to set the WAVEFORMATEXTENSIBLE dwChannelMask (channel order mask) in a poly WAV file that doesn't yet have a channel mask set.

  


  Can ffmpeg do this ? If not, is there another tool that can do this ?

  


• Copying audio stream from a source file to a trancoded video file using ffmpeg

  17 août 2012, par Gary

  I have built my own video-only transcoder using ffmpeg without audio. I do not want to transcode the audio. What will be best way to add the audio stream from the source file to the transcoded file using FFMPEG API ?