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• How to save an SDL bitmap to memory and load it back ?

  19 novembre 2012, par Nav

  I have a bunch of RWops functions :

  static int myseekfunc(SDL_RWops *context, int offset, int whence) { SDL_SetError("Can't seek in this kind of RWops"); return(-1); }
  
  static int myreadfunc(SDL_RWops *context, void *ptr, int size, int maxnum) { memset(ptr,0,size*maxnum); return(maxnum); }
  
  static int mywritefunc(SDL_RWops *context, const void *ptr, int size, int num) { return(num); }
  
  static int myclosefunc(SDL_RWops *context) 
  
  { 
  
    if(context->type != 0xdeadbeef) { SDL_SetError("Wrong kind of RWops for myclosefunc()"); return(-1); }
  
    free(context->hidden.unknown.data1);
  
    SDL_FreeRW(context);
  
    return(0);
  
  }
  
  
  
  // Note that this function is NOT static -- we want it directly callable from other source files 
  
  SDL_RWops *MyCustomRWop()
  
  {
  
    SDL_RWops *c=SDL_AllocRW();
  
    if(c==NULL) return(NULL);
  
  
  
    c->seek =myseekfunc;
  
    c->read =myreadfunc;
  
    c->write=mywritefunc;
  
    c->close=myclosefunc;
  
    c->type =0xdeadbeef;
  
    printf("deadbeef=%d\n",c->type);
  
    c->hidden.unknown.data1=malloc(256);//IS THIS CORRECT?
  
    return(c);
  
  }

  with which I'm trying to write a BMP into memory and then extract it back. The below code is from tutorial02.
  Two problems I'm facing are :
  1. Unless I call SDL_DisplayYUVOverlay, the SDL_SaveBMP function outputs a blank BMP file to the hard disk. How can I output a BMP file without having to call SDL_DisplayYUVOverlay ?
  2. Although I'm able to save the BMP to memory with SDL_SaveBMP_RW and free the memory with filestream->close, I'm unable to load the BMP back from memory with SDL_SaveBMP. The application crashes while trying to load it. Is it because of the c->hidden.unknown.data1=malloc(256); code above ? What would be the right way of allocating this memory ?

    AVFormatContext *pFormatCtx = NULL;
  
    int             i, videoStream;
  
    AVCodecContext  *pCodecCtx = NULL;
  
    AVCodec         *pCodec = NULL;
  
    AVFrame         *pFrame = NULL; 
  
    AVPacket        packet;
  
    SDL_Overlay     *bmp = NULL;
  
    SDL_Surface     *screen = NULL;
  
    SDL_Surface     *screen2 = NULL;
  
    SDL_Rect        rect;
  
  ....
  
  ....    
  
  if(frameFinished) 
  
  
  
  {
  
  SDL_LockYUVOverlay(bmp);//-----------lock
  
  
  
  AVPicture pict;
  
  pict.data[0] = bmp->pixels[0];
  
  pict.data[1] = bmp->pixels[2];
  
  pict.data[2] = bmp->pixels[1];
  
  
  
  pict.linesize[0] = bmp->pitches[0];
  
  pict.linesize[1] = bmp->pitches[2];
  
  pict.linesize[2] = bmp->pitches[1];
  
  
  
  // Convert the image into YUV format that SDL uses
  
  sws_scale( sws_ctx, (uint8_t const * const *)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pict.data, pict.linesize );
  
  
  
  SDL_UnlockYUVOverlay(bmp);//-----------unlock
  
  
  
  rect.x = 0;
  
  rect.y = 0;
  
  rect.w = pCodecCtx->width;
  
  rect.h = pCodecCtx->height;
  
  SDL_DisplayYUVOverlay(bmp, &rect);
  
  ++i;
  
  
  
  SDL_RWops *filestream = MyCustomRWop();//SDL_AllocRW();
  
  SDL_SaveBMP_RW (screen, filestream, i);
  
  screen2 = SDL_LoadBMP_RW(filestream,1);//LOADING IS THE PROBLEM HERE. DON'T KNOW WHY
  
  filestream->close;
  
  SDL_SaveBMP(screen, filepointer);

• FFMPEG - errors when combining videos

  1er décembre 2012, par ethrbunny

  I have two .OGG files of similar size, FPS and duration. My goal is to combine them into a side-by-side presentation using FFMPEG. To this end I've tried the following cmd :

  ffmpeg -i subject.ogg -vf "[in]pad=3*iw:3*ih[left] ;movie=clinician.ogg[right] ;[left] [right]overlay=100:0[out]" combined.ogg

  Suffice to say that the resultant video is non-playable. During the combination process FFMPEG prints lots of errors that read like :

  [Parsed_overlay_2 @ 0x1eb7d3e0] Buffer queue overflow, dropping

  What is this telling me ?

  Note :

  • both source files are playable
  • I padded the 'output' to be rather large in an attempt to understand the params
  • the placement of the 2nd video at 100:0 is arbitrary. Once I get the cmd working I'll move it to a better location in the output.
  • both videos began life as .FLV recorded from web cameras. I converted them to .ogg as FFMPEG didn't want to combine two .FLV files. If there is a better route to this, please let me know.

  So - what's wrong with my parameters and what am I doing to cause these FFMPEG errors ?

  EDIT :
  ffmpeg -i clinician.ogg

  Input #0, ogg, from 'clinician.ogg' :
  Duration : 00:05:20.98, start : 0.001000, bitrate : 2273 kb/s
  Stream #0:0 : Video : theora, yuv420p, 500x500 [SAR 1:1 DAR 1:1], 1k tbr, 1k tbn, 1k tbc
  Metadata :
  SERVER : Red5 Server 1.0.0 RC1 $Rev : 4193 $
  CANSEEKTOEND : true
  ENCODER : Lavf54.31.100
  Stream #0:1 : Audio : vorbis, 8000 Hz, stereo, s16
  Metadata :
  SERVER : Red5 Server 1.0.0 RC1 $Rev : 4193 $
  CANSEEKTOEND : true
  ENCODER : Lavf54.31.100

  ffmpeg -i subject.ogg

  Input #0, ogg, from 'subject.ogg' :
  Duration : 00:05:17.60, start : 0.001000, bitrate : 1341 kb/s
  Stream #0:0 : Video : theora, yuv420p, 300x300 [SAR 1:1 DAR 1:1], 83.33 tbr, 1k tbn, 1k tbc
  Metadata :
  SERVER : Red5 Server 1.0.0 RC1 $Rev : 4193 $
  CANSEEKTOEND : true
  ENCODER : Lavf54.31.100
  Stream #0:1 : Audio : vorbis, 8000 Hz, stereo, s16
  Metadata :
  SERVER : Red5 Server 1.0.0 RC1 $Rev : 4193 $
  CANSEEKTOEND : true
  ENCODER : Lavf54.31.100

• Decoder crashes after ffmpeg upgrade

  5 mai 2014, par Igor R.

  Recently I upgraded ffmpeg from 0.9 to 1.0 (tested on Win7x64 and on iOS), and now avcodec_decode_video2 seagfaults. Long story short : the crash occurs every time the video dimensions change (eg. from 320x240 to 160x120 or vice versa).

  I receive mpeg4 video stream from some proprietary source and decode it like this :

  // once, during initialization:
  
  AVCodec *codec_ = avcodec_find_decoder(CODEC_ID_MPEG4);
  
  AVCodecContext ctx_ = avcodec_alloc_context3(codec_);
  
  avcodec_open2(ctx_, codec_, 0);
  
  AVPacket packet_;
  
  av_init_packet(&packet_);
  
  AVFrame picture_ = avcodec_alloc_frame();
  
  
  
  // on every frame:
  
  int got_picture;
  
  packet_.size = size;
  
  packet_.data = (uint8_t *)buffer;
  
  avcodec_decode_video2(ctx_, picture_, &got_picture, &packet_);

  Again, all the above had worked flawlessly until I upgraded to 1.0. Now every time the frame dimensions change - avcodec_decode_video2 crashes. Note that I don’t assign width/height in AVCodecContext - neither in the beginning, nor when the stream changes - can it be the reason ?

  I’d appreciate any idea !

  Update : setting ctx_.width and ctx_.height doesn’t help.

  Update2 : just before the crash I get the following log messages :

  mpeg4, level 24 : "Found 2 unreleased buffers !".
  level 8 : "Assertion i < avci->buffer_count failed at libavcodec/utils.c:603"

  Update3 upgrading to 1.1.2 fixed this crash. The decoder is able again to cope with dimensions change on the fly.