AAC---ffmpeg转码 参考/dec/sample/transcode_aac.c示例代码

transcode_aac流程：

init_resampler重采样初始化
av_audio_fifo_alloc(output_codec_context->sample_fmt,output_codec_context->channels, 1)
	//	只要一帧Sample buffer




avformat_write_header(output_format_context, NULL))
while (1) {
      /* Use the encoder's desired frame size for processing. */
      const int output_frame_size = output_codec_context->frame_size;
      int finished                = 0;

      /* Make sure that there is one frame worth of samples in the FIFO
       * buffer so that the encoder can do its work.
       * Since the decoder's and the encoder's frame size may differ, we
       * need to FIFO buffer to store as many frames worth of input samples
       * that they make up at least one frame worth of output samples. */
      while (av_audio_fifo_size(fifo) < output_frame_size) {
          /* Decode one frame worth of audio samples, convert it to the
           * output sample format and put it into the FIFO buffer. */
          if (read_decode_convert_and_store(fifo, input_format_context,
                                            input_codec_context,
                                            output_codec_context,
                                            resample_context, &finished))
              goto cleanup;

          /* If we are at the end of the input file, we continue
           * encoding the remaining audio samples to the output file. */
          if (finished)
              break;
      }

      /* If we have enough samples for the encoder, we encode them.
       * At the end of the file, we pass the remaining samples to
       * the encoder. */
      while (av_audio_fifo_size(fifo) >= output_frame_size ||
             (finished && av_audio_fifo_size(fifo) > 0))
          /* Take one frame worth of audio samples from the FIFO buffer,
           * encode it and write it to the output file. */
          if (load_encode_and_write(fifo, output_format_context,
                                    output_codec_context))
              goto cleanup;

      /* If we are at the end of the input file and have encoded
       * all remaining samples, we can exit this loop and finish. */
      if (finished) {
          int data_written;
          /* Flush the encoder as it may have delayed frames. */
          do {
              data_written = 0;
              if (encode_audio_frame(NULL, output_format_context,
                                     output_codec_context, &data_written))
                  goto cleanup;
          } while (data_written);
          break;
      }
  }

    /* Write the trailer of the output file container. */