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• avfilter/vf_libplacebo : add flexible crop exprs

  1er mai 2023, par Niklas Haas

  avfilter/vf_libplacebo : add flexible crop exprs
  Motivated by a desire to use vf_libplacebo as a GPU-accelerated
  
  cropping/padding/zooming filter. This commit adds support for setting
  
  the `input/target.crop` fields as dynamic expressions.
  Re-use the same generic variables available to other scale and crop type
  
  filters, and also add some more that we can afford as a result of being
  
  able to set these properties dynamically.
  It's worth pointing out that `out_t/ot` is currently redundant with
  
  `in_t/t` since it will always contain the same PTS values, but I plan on
  
  changing this in the near future.
  I decided to also expose `crop_w/crop_h` and `pos_w/pos_h` as variables
  
  in the expression parser itself, since this enables the fairly common
  
  use case of determining dimensions first and then placing the image
  
  appropriately, such as is done in the default behavior (which centers
  
  the cropped/placed region by default).
  

  • [DH] doc/filters.texi
  • [DH] libavfilter/vf_libplacebo.c

• VP9 tiled encoding for view-port dependent 360-degree VR streaming

  28 janvier 2021, par Victor Coyter

  I am trying to use libvpx-vp9 to encode a 360-degree VR video and generate multi-bitrate viewport-dependent playlist, that is :

  


  

  • A video stream could be splitted in to n*m tiles (e.g., 8x8)

  


  • Users may fetch those high-resolution tiles which insides their view-port via HTTP webm

  


  • and fetch low-resolution tiles which outsides their view-port

  


  • Finally, combine the video (without decoding) and render with OpenGL shaders

  


  


  Similar ideas like OMAF has been implemented by Intel / fraunhofer hhi, but they were using H.265.

  


  Is that possible to implement in VP9 ?

  


  The tiles in VP9 is designed to accelerate the encoding process by multi-threading, but as per defined in VP9 bitstream specifications, a tile is a "rectangular region of the frame that could be able to be decoded and encoded independently"

  


  I can find that libvpx provide options : --tile-rows and --tile-column and can successfully run them, while they indeed use multi-thread to encode.

  


• avcodec/cbs : ensure user_data is padded for GBC parsing

  5 octobre 2018, par Aman Gupta

  avcodec/cbs : ensure user_data is padded for GBC parsing
  Fixes crash noticed in the cbs_userdata patchset.
  ====ERROR : AddressSanitizer : heap-buffer-overflow on address 0x609000026c89 at pc 0x00010725d37b bp 0x7ffeea04e750 sp 0x7ffeea04e748
  
  READ of size 4 at 0x609000026c89 thread T0
  
      #0 0x10725d37a in ff_cbs_read_unsigned get_bits.h:274
  
      #1 0x1072d2767 in ff_cbs_read_a53_user_data cbs_misc_syntax_template.c:119
  
      #2 0x1078251a7 in h264_metadata_filter h264_metadata_bsf.c:595
  
      #3 0x105c1321d in output_packet ffmpeg.c:853
  0x609000026c89 is located 1 bytes to the right of 8-byte region [0x609000026c80,0x609000026c88)
  
  allocated by thread T0 here :
  
      #0 0x10aef08d7 in wrap_posix_memalign (libclang_rt.asan_osx_dynamic.dylib:x86_64h+0x578d7)
  
      #1 0x10aca95e6 in av_malloc mem.c:87
  
      #2 0x10ac545fe in av_buffer_allocz buffer.c:72
  
      #3 0x107263b27 in cbs_h264_read_nal_unit cbs_h264_syntax_template.c:722
  
      #4 0x10725b688 in cbs_read_fragment_content cbs.c:155
  Signed-off-by : Aman Gupta <aman@tmm1.net>
  

  • [DH] libavcodec/cbs_h264_syntax_template.c
  • [DH] libavcodec/cbs_mpeg2_syntax_template.c