[FFmpeg-user] Understanding Encoding and Decoding frames

[Jaikishan]

Hello,

I am trying to add some data in a video frame and then rewrite a new video again
with the modified frames. The intention is to get that data back again after
reading the frames from the new video.

My input is a flv file and output is also a flv file. From the input flv file, I
can read the frames and decode them as given in many examples. 

 // Read frames and save first five frames to disk
  i=0;
  while(av_read_frame(pFormatCtx, &packet)>=0) {
    // Is this a packet from the video stream?
    if(packet.stream_index==videoStream) {
      // Decode video frame
      avcodec_decode_video(pCodecCtx, pFrame, &frameFinished, 
			   packet.data, packet.size);
      
      // Did we get a video frame?
      if(frameFinished) {
         // video frame in pFrame
         // Add the data
      }
    }
    
    // Free the packet that was allocated by av_read_frame
    av_free_packet(&packet);
  }

But, now if try to add my data in pFrame (without decoding the packet), and then
encode it back for the new video, I suspect that the data that I add will get
lost during the encoding process. Therefore, in order to make sure that I add
data such that they don't get lost, I need to understand how encoding works.
When I looked at avcodec_encode_video, it makes use of a function "encode". Now
I am trying to find the source code of this function but so far could not find
so in doxygen. I was wondering if somebody can explain how does encoding of
video frame works, specially in flv files.