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• avcodec/hevc_filter : Pass HEVCLocalContext when slice-threading

  29 juin 2022, par Andreas Rheinhardt

  avcodec/hevc_filter : Pass HEVCLocalContext when slice-threading
  The HEVC decoder has both HEVCContext and HEVCLocalContext
  
  structures. The latter is supposed to be the structure
  
  containing the per-slicethread state.
  Yet that is not how it is handled in practice : Each HEVCLocalContext
  
  has a unique HEVCContext allocated for it and each of these
  
  coincides with the main HEVCContext except in exactly one field :
  
  The corresponding HEVCLocalContext.
  
  This makes it possible to pass the HEVCContext everywhere where
  
  logically a HEVCLocalContext should be used.
  This commit stops doing this for lavc/hevc_filter.c ; it also constifies
  
  everything that is possible in order to ensure that no slice thread
  
  accidentally modifies the main HEVCContext state.
  There are places where this was not possible, namely with the SAOParams
  
  in sao_filter_CTB() or with sao_pixels_buffer_h in copy_CTB_to_hv().
  
  Both of these instances lead to data races, see
  
  https://fate.ffmpeg.org/report.cgi?time=20220629145651&slot=x86_64-archlinux-gcc-tsan-slices
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/hevc_filter.c
  • [DH] libavcodec/hevcdec.c
  • [DH] libavcodec/hevcdec.h

• Coordinates with file format .ASS

  29 mai 2024, par Alex

  I'm grabbing my text coordinates that I want to use for the file format .ASS and for centering on a 1080 by 1920 video, I have an application that displays where the text is on the video and can retrieve the position, an example of centered position is 310 by 800. When I try to set the position of the text inside the .ASS with those positions it doesn't write the caption where is meant to be. Could some explain how a .ASS positioning works. If use 200 px by 200 px as positioning it places it way further than the center even though the video its a 1080x1920 video, shouldn't it be placed before the center position of the video ?

  


  This is how my .ASS file looks like, I'm using ffmpeg to write the subtitles into the video :

  


  [Script Info]
Title: Video Subtitles
ScriptType: v4.00+
Collisions: Normal
PlayDepth: 0
PlayResX: 1080
PlayResY: 1920


[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BorderStyle, Encoding
Style: Default, Segoe UI,9,&H00FFFFFF,&HFFFF00,&H00FFFFFF,0,0
Style: Background, Segoe UI,9,&H00FFFFFF,&H000000FF,&H00000000,3,0

[Events]
Format: Start, End, Style, MarginL, MarginR, MarginV, Text
Dialogue: 0:00:00.00,0:00:05.00,Default,0,0,0,{\pos(275,876)} {\bord5\3c&H000000&\fs90}LISTEN IN {\r}



  


  

  • Edit : I've added the playresx and y, but the text is still not where its meant to be. To add a bit more context, I have a scene in PyQT that uses a coordinates system to place text over videos, for this text its saying that its at the x axis of 275 and y axis of 876. When I use those coordinates for the .ASS text it doesn't show the same position. Also the scene in which the video and the text is in, its 1080 by 1920, this images show what I want and what I'm getting :

  


  


  

  


  

  


• ffmpeg buffer not released

  11 mars 2013, par ByteByter

  So, I have written a basic decoder for ffmpeg that simply reads the input frames pixel data (Stored using RGB 8 format), and places it directly into the output buffer. (Also RGB 8) The problem is that when I use this decoder in ffmpeg, it says that there is 1 unreleased buffer.(Tested using ffmpeg -i Test.utah Test.png). Unfortunately, I am unsure of what buffer it is talking about, as I am not creating my own buffer. I have tried releasing the AVContext's coded_frame buffer in my decoders closing method, but this causes segmentation faults.

  Any help would be greatly appreciated.

  static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame, AVPacket *avpkt)
  
  {
  
      int ret;           /*Hold return from get_buffer */ 
  
      int skipSize;      /*Number of dummy bytes to skip per line*/
  
      int fseek=8;       /*Location of the first pixel*/
  
      int i=0; int j=0;  /*Output buffer seek index/Input Buffer seek index*/
  
      const uint8_t *buf = avpkt->data; /*Hold a pointer to the input buffer*/
  
      AVFrame *pict=data; /*Hold a pointer to the output buffer*/
  
  
  
      /*Set the output pixel format to RGB8*/
  
      avctx->pix_fmt = AV_PIX_FMT_RGB8;
  
  
  
      /*Get the width and height*/
  
      bytestream_get_le32(&buf);
  
      avctx->width=bytestream_get_le16(&buf);
  
      avctx->height=bytestream_get_le16(&buf);
  
  
  
      /*Release the old buffer*/
  
      if (pict->data[0]) avctx->release_buffer(avctx, pict);
  
  
  
      /*Aquire a large enough data buffer to hold the decompressed picture*/
  
      if (ret=ff_get_buffer(avctx, pict) < 0) return ret;
  
      skipSize=pict->linesize[0] - avctx->width; 
  
  
  
      /*Transfer input buffer to output buffer*/
  
      for(int y=0;yheight;y++){
  
          for(int x=0;xwidth;x++){
  
              pict->data[0][i]=avpkt->data[fseek+j];
  
              j++;
  
              i++;
  
          }
  
          i+=skipSize;
  
      }
  
  
  
      /*Inform ffmpeg the output is a key frame and that it is ready for external usage*/
  
      pict->pict_type        = AV_PICTURE_TYPE_I;
  
      pict->key_frame        = 1;
  
      *got_frame=1;
  
      return 0;
  
  }