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• Including objects to a shared library from a C++ archive (.a)

  1er septembre 2021, par El Sampsa

  I am trying to include some object files into a shared library I am building. Take the following command (things in [ETC] have been omitted for brevity) :

  



  


  /usr/bin/c++ -fPIC -std=c++14 -pthread -Iinclude/ext/liveMedia -Iinclude/ext/groupsock [ETC] -g -shared -Wl,-soname,libValkka.so -o lib/libValkka.so CMakeFiles/Valkka.dir/src/avthread.cpp.o CMakeFiles/Valkka.dir/src/opengl.cpp.o [ETC] CMakeFiles/Valkka.dir/src/decoders.cpp.o -lX11 -lGLEW -lGLU -lGL -Wl,—whole-archive lib/libavcodec.a -Wl,—no-whole-archive

  


  



  So basically I am just creating a shared library where most of the objects come from my own source code (i.e. CMakeFiles/Valkka.dir/src/*.o), but some of them come from an external static library, located at "lib/libavcodec.a". I get the following error :

  



  


  /usr/bin/ld : lib/libavcodec.a(h264_cabac.o) : relocation R_X86_64_PC32 against symbol 'ff_h264_cabac_tables' can not be used when making a shared object ; recompile with -fPIC
 /usr/bin/ld : final link failed : Bad value
 collect2 : error : ld returned 1 exit status

  


  



  But that is so untrue ! I can extract "libavcodec.a" with

  



  ar x libavcodec.a


  



  And after that check that

  



  readelf --relocs h264_cabac.o | egrep '(GOT|PLT|JU?MP_SLOT)' 


  



  does give some **it :

  



  


  00000000175d 003100000004 R_X86_64_PLT32 0000000000000000 __stack_chk_fail - 4
 000000001926 003100000004 R_X86_64_PLT32 0000000000000000 __stack_chk_fail - 4

  
 


  ...

  


  



  As does

  



  objdump -r h264_cabac.o | grep -i "relocation"


  



  So, indeed, the object files in "libavcodec.a" have been compiled to get PIC (position independent code).

  



  Why does the linker believe otherwise !?

  



  Related links :

  



  How to include all objects of an archive in a shared object ?

  



  Linking archives (.a) into shared object (.so)

  



  Is there a way to determine that a .a or .so library has been compiled as position indepenent code ?

  



  How can I tell, with something like objdump, if an object file has been built with -fPIC ?

  


• Why won’t this mp4 play in a video-js tag any longer

  18 octobre 2019, par Velocedge

  I’m using ffmpeg to convert files to MP4. I’ve made some modifications to the ffmpeg string but now it seems no matter what I use, the video won’t play in an HTML5 tag (Chrome browser). Normally, I just used "-vcodec libx264 -s 1280x720 -ar 22050". When I try to load it in the video tag, I get the following error on http://family.gotsport.net/lmw/GotSport/videoPlayer.asp?WS=1&URL=/VideoFiles/2/4_70_highlight :

  The media could not be loaded, either because the server or network failed or because the format is not supported.

  No matter what parameters I use (or don’t use), it still won’t play. However, if you just call the url directly, it will play in Chrome (http://family.gotsport.net/videofiles/2/2_70_highlight.mp4). I’m using the 7.0.0 version of video-js from their CDN (although older versions give the same result).

  Video tag looks like :

  <video class="video-js vjs-default-skin" autoplay="autoplay" controls="controls" preload="auto"> 
  
      <source src="/VideoFiles/2/4_70_highlight.mp4" type="video/mp4"></source>
  
  </video> 

  Here is the MediaInfo output from the file that won’t play :

  General
  
  Complete name                            : E:\VideoFiles\2\2_70_highlight.mp4
  
  Format                                   : MPEG-4
  
  Format profile                           : Base Media
  
  Codec ID                                 : isom (isom/iso2/avc1/mp41)
  
  File size                                : 5.87 MiB
  
  Duration                                 : 27 s 60 ms
  
  Overall bit rate                         : 1 820 kb/s
  
  Writing application                      : Lavf58.29.100
  
  
  
  Video
  
  ID                                       : 1
  
  Format                                   : AVC
  
  Format/Info                              : Advanced Video Codec
  
  Format profile                           : High@L3.1
  
  Format settings                          : CABAC / 4 Ref Frames
  
  Format settings, CABAC                   : Yes
  
  Format settings, Reference frames        : 4 frames
  
  Codec ID                                 : avc1
  
  Codec ID/Info                            : Advanced Video Coding
  
  Duration                                 : 27 s 60 ms
  
  Bit rate                                 : 1 685 kb/s
  
  Width                                    : 1 280 pixels
  
  Height                                   : 720 pixels
  
  Display aspect ratio                     : 16:9
  
  Frame rate mode                          : Constant
  
  Frame rate                               : 29.970 (29970/1000) FPS
  
  Color space                              : YUV
  
  Chroma subsampling                       : 4:2:0
  
  Bit depth                                : 8 bits
  
  Scan type                                : Progressive
  
  Bits/(Pixel*Frame)                       : 0.061
  
  Stream size                              : 5.44 MiB (93%)
  
  Writing library                          : x264 core 158 r2984 3759fcb
  
  Encoding settings                        : cabac=1 / ref=3 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=12 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=crf / mbtree=1 / crf=23.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
  
  Codec configuration box                  : avcC
  
  
  
  Audio
  
  ID                                       : 2
  
  Format                                   : AAC LC
  
  Format/Info                              : Advanced Audio Codec Low Complexity
  
  Codec ID                                 : mp4a-40-2
  
  Duration                                 : 27 s 22 ms
  
  Duration_LastFrame                       : -6 ms
  
  Bit rate mode                            : Constant
  
  Bit rate                                 : 128 kb/s
  
  Channel(s)                               : 2 channels
  
  Channel layout                           : L R
  
  Sampling rate                            : 22.05 kHz
  
  Frame rate                               : 21.533 FPS (1024 SPF)
  
  Compression mode                         : Lossy
  
  Stream size                              : 423 KiB (7%)
  
  Default                                  : Yes
  
  Alternate group                          : 1

  Do you see anything that would keep this format from playing in an HTML5 video tag ?

• Setting dpi flag in image files generated using ffmpeg

  17 mars 2023, par jim_e_jib

  We're using ffmpeg to batch out some TIFF images that are being resized and having white borders created to fit specific paper sizes.

  


  The resulting images default to 72dpi, even when the source is 300dpi. Is there a way to set the dpi flag in the output file ?

  


  Many thanks :-)

  


  The command we're using :

  


  for %%a in ("*.tif") do ffmpeg -i "%%a" -vf "scale=6974:4919:force_original_aspect_ratio=decrease,pad=7016:4961:(ow-iw)/2:(oh-ih)/2:color=white, format=rgb24" "%%~na A2 poster 594x420mm-Border.tif"


  


  We have tried using -dpi 300 in the code but get the error that this is not a recognised.

  


  Edit :

  


  I have just managed to answer my own question :

  


  for %%a in ("*.tif") do ffmpeg -i "%%a" -vf "scale=6974:4919:force_original_aspect_ratio=decrease,pad=7016:4961:(ow-iw)/2:(oh-ih)/2:color=white,format=rgb24" -dpi 300 "%%~na A2 poster 594x420mm-Border.tif"


  


  I had been placing the -dpi 300 in the wrong place when I'd tried it...