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• Creating a usable H.264 video file

  4 mai 2019, par Ethan McTague

  I am trying to use libavcodec to generate an mp4 video file from individual frames. Each input frame is a qt QImage, and the output file is written to using the Qt QFile class.

  I’ve done this through a VideoTarget class which opens the given ’target’ file when initialized, records frames when addFrame(image) is called, and then saves/closes the file when its destructor is called.

  The class has the following fields :

  AVCodec* m_codec = nullptr;
  
  AVCodecContext *m_context = nullptr;
  
  AVPacket* m_packet = nullptr;
  
  AVFrame* m_frame = nullptr;
  
  
  
  QFile m_target;

  And looks like this :

  VideoTarget::VideoTarget(QString target, QObject *parent) : QObject(parent), m_target(target)
  
  {
  
      // Find video codec
  
      m_codec = avcodec_find_encoder_by_name("libx264rgb");
  
      if (!m_codec) throw std::runtime_error("Unable to find codec.");
  
  
  
      // Make codec context
  
      m_context = avcodec_alloc_context3(m_codec);
  
      if (!m_context) throw std::runtime_error("Unable to allocate codec context.");
  
  
  
      // Make codec packet
  
      m_packet = av_packet_alloc();
  
      if (!m_packet) throw std::runtime_error("Unable to allocate packet.");
  
  
  
      // Configure context
  
      m_context->bit_rate = 400000;
  
      m_context->width = 1280;
  
      m_context->height = 720;
  
      m_context->time_base = (AVRational){1, 60};
  
      m_context->framerate = (AVRational){60, 1};
  
      m_context->gop_size = 10;
  
      m_context->max_b_frames = 1;
  
      m_context->pix_fmt = AV_PIX_FMT_RGB24;
  
  
  
      if (m_codec->id == AV_CODEC_ID_H264)
  
          av_opt_set(m_context->priv_data, "preset", "slow", 0);
  
  
  
      // Open Codec
  
      int ret = avcodec_open2(m_context, m_codec, nullptr);
  
      if (ret < 0) {
  
          throw std::runtime_error("Unable to open codec.");
  
      }
  
  
  
      // Open file
  
      if (!m_target.open(QIODevice::WriteOnly))
  
          throw std::runtime_error("Unable to open target file.");
  
  
  
      // Allocate frame
  
      m_frame = av_frame_alloc();
  
      if (!m_frame) throw std::runtime_error("Unable to allocate frame.");
  
  
  
      m_frame->format = m_context->pix_fmt;
  
      m_frame->width = m_context->width;
  
      m_frame->height = m_context->height;
  
      m_frame->pts = 0;
  
  
  
      ret = av_frame_get_buffer(m_frame, 24);
  
      if (ret < 0) throw std::runtime_error("Unable to allocate frame buffer.");
  
  }
  
  
  
  void VideoTarget::addFrame(QImage &image)
  
  {
  
      // Ensure frame data is writable
  
      int ret = av_frame_make_writable(m_frame);
  
      if (ret < 0) throw std::runtime_error("Unable to make frame writable.");
  
  
  
      // Prepare image
  
      for (int y = 0; y < m_context->height; y++) {
  
          for (int x = 0; x < m_context->width; x++) {
  
              auto pixel = image.pixelColor(x, y);
  
              int pos = (y * 1024 + x) * 3;
  
              m_frame->data[0][pos] = pixel.red();
  
              m_frame->data[0][pos + 1] = pixel.green();
  
              m_frame->data[0][pos + 2] = pixel.blue();
  
          }
  
      }
  
  
  
      m_frame->pts++;
  
  
  
      // Send the frame
  
      ret = avcodec_send_frame(m_context, m_frame);
  
      if (ret < 0) throw std::runtime_error("Unable to send AV frame.");
  
  
  
      while (ret >= 0) {
  
          ret = avcodec_receive_packet(m_context, m_packet);
  
          if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
  
              return;
  
          else if (ret < 0) throw std::runtime_error("Error during encoding.");
  
  
  
          m_target.write((const char*)m_packet->data, m_packet->size);
  
          av_packet_unref(m_packet);
  
      }
  
  }
  
  
  
  VideoTarget::~VideoTarget()
  
  {
  
      int ret = avcodec_send_frame(m_context, nullptr);
  
      if (ret < 0) throw std::runtime_error("Unable to send AV null frame.");
  
  
  
      while (ret >= 0) {
  
          ret = avcodec_receive_packet(m_context, m_packet);
  
          if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
  
              return;
  
          else if (ret < 0) throw std::runtime_error("Error during encoding.");
  
  
  
          m_target.write((const char*)m_packet->data, m_packet->size);
  
          av_packet_unref(m_packet);
  
      }
  
  
  
      // Magic number at the end of the file
  
      uint8_t endcode[] = { 0, 0, 1, 0xb7 };
  
      m_target.write((const char*)endcode, sizeof(endcode));
  
      m_target.close();
  
  
  
      // Free codec stuff
  
      avcodec_free_context(&m_context);
  
      av_frame_free(&m_frame);
  
      av_packet_free(&m_packet);
  
  }

  When used, the class seems to work, and data is written to the file, except I am unable to play back the resulting file in any application.

  My main suspect is these lines :

      // Prepare image
  
      for (int y = 0; y < m_context->height; y++) {
  
          for (int x = 0; x < m_context->width; x++) {
  
              auto pixel = image.pixelColor(x, y);
  
              int pos = (y * 1024 + x) * 3;
  
              m_frame->data[0][pos] = pixel.red();
  
              m_frame->data[0][pos + 1] = pixel.green();
  
              m_frame->data[0][pos + 2] = pixel.blue();
  
          }
  
      }

  The libavcodec documentation was extremely vague regarding the layout of image data, so I effectively had to guess and be happy with the first thing that didn’t crash, so chances are I’m writing this incorrectly. There’s also the issue of size mismatch between my pixel color data calls (giving int values) and the 24-bits-per-pixel RGB format I have selected.

  How do I tweak this code to output actual, functioning video files ?

• How to encode using the FFMpeg in Android (using H263)

  10 mai 2019, par Kenny910

  I am trying to follow the sample code on encoding in the ffmpeg document and successfully build a application to encode and generate a mp4 file but I face the following problems :

  1) I am using the H263 for encoding but I can only set the width and height of the AVCodecContext to 176x144, for other case (like 720x480 or 640x480) it will return fail.

  2) I can’t play the output mp4 file by using the default Android player, isn’t it support H263 mp4 file ? p.s. I can play it by using other player

  3) Is there any sample code on encoding other video frame to make a new video (which mean decode the video and encode it back in different quality setting, also i would like to modify the frame content) ?

  Here is my code, thanks !

  JNIEXPORT jint JNICALL Java_com_ffmpeg_encoder_FFEncoder_nativeEncoder(JNIEnv* env, jobject thiz, jstring filename){
  
  
  
  LOGI("nativeEncoder()");
  
  
  
  avcodec_register_all();
  
  avcodec_init();
  
  av_register_all();
  
  
  
  AVCodec         *codec;
  
  AVCodecContext  *codecCtx;
  
  int             i;
  
  int             out_size;
  
  int             size;
  
  int             x;
  
  int             y;
  
  int             output_buffer_size;
  
  FILE            *file;
  
  AVFrame         *picture;
  
  uint8_t         *output_buffer;
  
  uint8_t         *picture_buffer;
  
  
  
  /* Manual Variables */
  
  int             l;
  
  int             fps = 30;
  
  int             videoLength = 5;
  
  
  
  /* find the H263 video encoder */
  
  codec = avcodec_find_encoder(CODEC_ID_H263);
  
  if (!codec) {
  
      LOGI("avcodec_find_encoder() run fail.");
  
  }
  
  
  
  codecCtx = avcodec_alloc_context();
  
  picture = avcodec_alloc_frame();
  
  
  
  /* put sample parameters */
  
  codecCtx->bit_rate = 400000;
  
  /* resolution must be a multiple of two */
  
  codecCtx->width = 176;
  
  codecCtx->height = 144;
  
  /* frames per second */
  
  codecCtx->time_base = (AVRational){1,fps};
  
  codecCtx->pix_fmt = PIX_FMT_YUV420P;
  
  codecCtx->codec_id = CODEC_ID_H263;
  
  codecCtx->codec_type = AVMEDIA_TYPE_VIDEO;
  
  
  
  /* open it */
  
  if (avcodec_open(codecCtx, codec) < 0) {
  
      LOGI("avcodec_open() run fail.");
  
  }
  
  
  
  const char* mfileName = (*env)->GetStringUTFChars(env, filename, 0);
  
  
  
  file = fopen(mfileName, "wb");
  
  if (!file) {
  
      LOGI("fopen() run fail.");
  
  }
  
  
  
  (*env)->ReleaseStringUTFChars(env, filename, mfileName);
  
  
  
  /* alloc image and output buffer */
  
  output_buffer_size = 100000;
  
  output_buffer = malloc(output_buffer_size);
  
  
  
  size = codecCtx->width * codecCtx->height;
  
  picture_buffer = malloc((size * 3) / 2); /* size for YUV 420 */
  
  
  
  picture->data[0] = picture_buffer;
  
  picture->data[1] = picture->data[0] + size;
  
  picture->data[2] = picture->data[1] + size / 4;
  
  picture->linesize[0] = codecCtx->width;
  
  picture->linesize[1] = codecCtx->width / 2;
  
  picture->linesize[2] = codecCtx->width / 2;
  
  
  
  for(l=0;l/encode 1 second of video
  
      for(i=0;i/prepare a dummy image YCbCr
  
          //Y
  
          for(y=0;yheight;y++) {
  
              for(x=0;xwidth;x++) {
  
                  picture->data[0][y * picture->linesize[0] + x] = x + y + i * 3;
  
              }
  
          }
  
  
  
          //Cb and Cr
  
          for(y=0;yheight/2;y++) {
  
              for(x=0;xwidth/2;x++) {
  
                  picture->data[1][y * picture->linesize[1] + x] = 128 + y + i * 2;
  
                  picture->data[2][y * picture->linesize[2] + x] = 64 + x + i * 5;
  
              }
  
          }
  
  
  
          //encode the image
  
          out_size = avcodec_encode_video(codecCtx, output_buffer, output_buffer_size, picture);
  
          fwrite(output_buffer, 1, out_size, file);
  
      }
  
  
  
      //get the delayed frames
  
      for(; out_size; i++) {
  
          out_size = avcodec_encode_video(codecCtx, output_buffer, output_buffer_size, NULL);
  
          fwrite(output_buffer, 1, out_size, file);
  
      }
  
  }
  
  
  
  //add sequence end code to have a real mpeg file
  
  output_buffer[0] = 0x00;
  
  output_buffer[1] = 0x00;
  
  output_buffer[2] = 0x01;
  
  output_buffer[3] = 0xb7;
  
  
  
  fwrite(output_buffer, 1, 4, file);
  
  fclose(file);
  
  free(picture_buffer);
  
  free(output_buffer);
  
  avcodec_close(codecCtx);
  
  av_free(codecCtx);
  
  av_free(picture);
  
  
  
  LOGI("finish");
  
  
  
  return 0; }

• H264 decoding using ffmpeg

  18 mai 2019, par Kindermann

  I’m trying to decode a video stream with ffmpeg library, that’s how I do it basically :

  void video_decode(const char *filename)
  
  {
  
      AVCodec *codec;
  
      AVCodecContext *c= NULL;
  
      int frame_count=0;
  
      FILE *f;
  
      AVFrame *frame;
  
      uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
  
      AVPacket avpkt;
  
      av_init_packet(&avpkt);
  
      memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
  
      printf("Decoding video file...\n");
  
      /* find the h264 video decoder */
  
      codec = avcodec_find_decoder(AV_CODEC_ID_H264);
  
      c = avcodec_alloc_context3(codec);
  
      c->bit_rate = 400000;
  
      c->width = 1920;
  
      c->height = 1080;
  
  
  
      if (avcodec_open2(c, codec, NULL) < 0) {
  
          fprintf(stderr, "Could not open codec\n");
  
          exit(1);
  
      }
  
      frame = av_frame_alloc();
  
      for (;;) {
  
          avpkt.size = fread(inbuf, 1, INBUF_SIZE, f);         
  
      if (avpkt.size == 0)
  
              break;
  
          avpkt.data = inbuf;
  
          while(avpkt.size > 0){
  
  
  
          int len, got_frame;
  
              len = avcodec_decode_video2(c, frame, &got_frame, &avpkt);          
  
          if (len < 0) {
  
                  fprintf(stderr, "Errr while decding frame %d\n", frame_count);
  
                  exit (1);
  
              }
  
              if (got_frame) {
  
                  //Print out frame information..
  
          }
  
              if (avpkt.data) {
  
                  avpkt.size -= len;
  
                  avpkt.data += len;
  
              }
  
      }               
  
      }  
  
  }

  But I got the following outputs :

  Decoding video file...
  
  [h264 @ 0x303c040] decode_slice_header error
  
  [h264 @ 0x303c040] decode_slice_header error
  
  [h264 @ 0x303c040] decode_slice_header error
  
  [h264 @ 0x303c040] no frame!
  
  Errr while decding frame 0

  Obviously the initiation of codec was incomplete. Do you have experience with h264 api ? Any help would be appreciated.