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• Why do .bss/.rodata symbols stay in binary after strip ?

  15 novembre 2014, par BlahGeek

  As far as I know, there’s only one kind of symbols in executable binary that is really needed, which is dynamic symbols. These symbols is used in relocation operation because they are dynamic linked. Static linked functions/variables, in the other hand, is not needed so can be stripped.

  However, when I was examining the stripped ffmpeg binary, this is what I got :

  >nm -D ffmpeg
  
  ...
  
                   U __vfprintf_chk
  
                   U __vsnprintf_chk
  
                   U write
  
  00000000018fa880 B x264_cabac_contexts
  
  0000000001052a40 R x264_cabac_range_lps
  
  0000000001052940 R x264_cabac_transition
  
  0000000001970580 B x264_cabac_transition_unary
  
  0000000001056820 R x264_last_coeff_flag_offset
  
  0000000001056860 R x264_significant_coeff_flag_offset
  
  0000000001056900 R x264_significant_coeff_flag_offset_8x8
  
                   U __xpg_strerror_r
  
                   U __xstat64
  
  ...

  I can verify that libx264 is static linked to ffmpeg :

  > ldd ffmpeg
  
  linux-vdso.so.1 =>  (0x00007fff26d61000)
  
  libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f7c707e7000)
  
  libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f7c704e1000)
  
  liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f7c702be000)
  
  libbz2.so.1.0 => /lib/x86_64-linux-gnu/libbz2.so.1.0 (0x00007f7c700ae000)
  
  libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f7c6fe95000)
  
  libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f7c6fc76000)
  
  libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f7c6f8b0000)
  
  /lib64/ld-linux-x86-64.so.2 (0x00007f7c70b0a000)
  
  libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f7c6f69a000)
  
  libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f7c6f495000)

  So, I don’t understand why symbols like x264_cabac_contexts is not stripped. (It’s defined in libx264/.../cabac.c) :

  uint8_t x264_cabac_contexts[4][QP_MAX_SPEC+1][1024];

  It bothered me for several hours and I’ve found nothing on google... Hope someone would explain this... Thanks in advance !

• php 5.3.13 ffmpeg Windows 7 64bit Not working wamp server [closed]

  28 juin 2018, par Waqas Ahmed

  I am facing following issue during installing the ffmpeg on the windows 7 64-bit machine using WampServer Version 2.2 with php 5.3.13 and ffmpeg extension 32-Bit

  I didn’t find ffmpeg ext. 32-bit..

  PHP Startup : Unable to load dynamic library ’c :/wamp/bin/php/php5.3.13/ext/php_ffmpeg.dll’ - %1 is not a valid Win32 application.

• How can I concatenate MP4 videos and exactly match this combined video to an audio track in ffmpeg ?

  17 juin 2020, par mattador

  Basically I want to combine 4 videos into a single video, then swap out the concatenated audio for another track. The audio track needs to be unaltered and sync exactly to the video.

  



  Specifically, I'm creating multipaged dynamic audio spectrograms (visualizations of a sound file) using ggplot2 and gganimate in R, which I want to combine using ffmpeg. So the original WAV is chopped up into 3 sec segments, a video is created to visualize frequency changes over time for each segment, which I want to combine into 1 video with the original audio track matched up.

  



  All of my relevant files are at github here in the vids folder : DL link here

  



  The individual dynamic spectrograms export fine (1-4.mp4 in the archive). They are each 20ms too long ; they should be exactly 3s, but otherwise great.

  



  I then use ffmpeg to concatenate them :

  



  ffmpeg -f concat -safe 0 -i "mp4Segments.txt" -codec copy -t 12 -y "(1-4)vid.mp4"


  



  but you can see the end of (1-4)vid.mp4 is getting a little off (the cursor is not all the way to the end, so I guess the video is getting cut off before the end. Not a deal-breaker, since the audio still aligns very well to the video cursor.

  



  Now, since the concatenated video introduces glitchy audio between clips, I want to take the uncut original audio and add that to the assembled video.

  



  ffmpeg -ss 0 -i "(1-4)vid.mp4" -i "origWAV.wav"  -c:v libx264 -map 0:v:0 -map 1:a:0 -c:a aac -ac 1 -b:a 192k -y -vsync 1 -t 12 "(1-4)vid+origWAV.mp4"


  



  but the audio is slightly off now, and ends even further before the end of the video. Since it's really important to align audio and video precisely for this, how can I speed up the video to fit the exact duration of the audio or otherwise fix this issue ?