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• Why is the library built for armv7 even though I set -march=armv6 ?

  13 juillet 2018, par Luca Carlon

  I’m trying to build libx264 for armv6, but what I get seems to be built for armv7. I’m using this configure line :

  ./configure --host=arm-linux-gnueabihf --enable-static --cross-prefix=${CCPREFIX} --prefix=... --extra-cflags='-march=armv6' --extra-ldflags='-march=armv6' --extra-asflags='-march=armv6'

  which results in an output like this :

  [...]
  
  arm-linux-gnueabihf-gcc -Wno-maybe-uninitialized -Wshadow -O3 -ffast-math  -Wall -I. -I. -march=armv6 -std=gnu99 -D_GNU_SOURCE -fomit-frame-pointer -fno-tree-vectorize   -c -o common/opencl.o common/opencl.c
  
  arm-linux-gnueabihf-gcc -Wno-maybe-uninitialized -Wshadow -O3 -ffast-math  -Wall -I. -I. -march=armv6 -std=gnu99 -D_GNU_SOURCE -fomit-frame-pointer -fno-tree-vectorize   -c -o encoder/slicetype-cl.o encoder/slicetype-cl.c
  
  arm-linux-gnueabihf-gcc -I. -I. -march=armv6 -c -DSTACK_ALIGNMENT=4 -DHIGH_BIT_DEPTH=0 -DBIT_DEPTH=8 -o common/arm/cpu-a.o common/arm/cpu-a.S
  
  [...]

  now this is what I see :

  $ readelf -A x264
  
  Attribute Section: aeabi
  
  File Attributes
  
    Tag_CPU_name: "7-A"
  
    Tag_CPU_arch: v7
  
    Tag_CPU_arch_profile: Application
  
    Tag_ARM_ISA_use: Yes
  
    Tag_THUMB_ISA_use: Thumb-2
  
    Tag_FP_arch: VFPv3
  
    Tag_Advanced_SIMD_arch: NEONv1
  
    Tag_ABI_PCS_wchar_t: 4
  
    Tag_ABI_FP_denormal: Needed
  
    Tag_ABI_FP_exceptions: Needed
  
    Tag_ABI_FP_number_model: IEEE 754
  
    Tag_ABI_align_needed: 8-byte
  
    Tag_ABI_enum_size: int
  
    Tag_ABI_HardFP_use: Deprecated
  
    Tag_ABI_VFP_args: VFP registers
  
    Tag_CPU_unaligned_access: v6
  
    Tag_DIV_use: Not allowed

  also I see this :

  $ readelf -A encoder/slicetype-cl.o
  
  Attribute Section: aeabi
  
  File Attributes
  
    Tag_CPU_name: "6"
  
    Tag_CPU_arch: v6
  
    Tag_ARM_ISA_use: Yes
  
    Tag_THUMB_ISA_use: Thumb-1
  
    Tag_FP_arch: VFPv2
  
    Tag_ABI_PCS_wchar_t: 4
  
    Tag_ABI_FP_number_model: Finite
  
    Tag_ABI_align_needed: 8-byte
  
    Tag_ABI_align_preserved: 8-byte, except leaf SP
  
    Tag_ABI_enum_size: int
  
    Tag_ABI_HardFP_use: Deprecated
  
    Tag_ABI_VFP_args: VFP registers
  
    Tag_ABI_optimization_goals: Aggressive Speed
  
    Tag_CPU_unaligned_access: v6

  but :

  $ readelf -A common/arm/cpu-a.o
  
  Attribute Section: aeabi
  
  File Attributes
  
    Tag_CPU_name: "7-A"
  
    Tag_CPU_arch: v7
  
    Tag_CPU_arch_profile: Application
  
    Tag_ARM_ISA_use: Yes
  
    Tag_THUMB_ISA_use: Thumb-2
  
    Tag_FP_arch: VFPv3
  
    Tag_Advanced_SIMD_arch: NEONv1

  Can someone explain why those commands seem to output an armv6 binary once but an armv7 binary in the other case ? May that be the reason why the resulting binary is marked as armv7 ?
  Thank you for any explanation.

• Proper reading of MP3 file disrupted by ID3 tags

  3 septembre 2016, par PookyFan

  My semestral project is due this Thursday and I have major problem with reading MP3 file (the project is about sound analysis, don’t ask my what exactly is it about and why I’m doing it so late).

  First, I read first 10 bytes to check for ID3 tags. If they’re present, I’ll just skip to the first MP3 header - or at least that’s the big idea. Here is how I count ID3 tag size :

  if (inbuf[0] == 'I' && inbuf[1] == 'D' && inbuf[2] == '3') //inbuf contains first 10 bytes from file
  
  {
  
      int size = inbuf[3] * 2097152 + inbuf[4] * 16384 + inbuf[5] * 128 + inbuf[6]; //Will change to binary shifts later
  
      //Do something else with it - skip rest of ID3 tags etc
  
  }

  It works ok for files without ID3 tags and for some files with them, but for some other files ffmpeg (which I use for decoding) returns "no header" error, which means it didn’t catch MP3 header correctly. I know that since if I remove ID3 from that .mp3 file (with Winamp for example), no errors occur. The conclusion is that size count algorithm isn’t always valid.

  So the question is : how do I get to know how big exactly is entire ID3 part of the .mp3 file (all possible tags, album picture and whatever) ? I’m looking for it everywhere but I just keep finding this algorithm I posted above. Sometimes also something about some 10 bytes footer I need to take into account, but it seems it frequently gets more than 10 bytes for it to eventually catch proper MP3 frame.

• my own tv news channel - using vlc streaming

  6 janvier 2015, par SledgehammerPL

  I want to create my own tv channel (using vlc streaming).
  And for now - it works great :

  cvlc --sout-keep --loop --sout '#standard{access=http,mux=ts,dst=:2000}' file.avi

  But i have two problems :

  1st : how to make a playlist, which i can modify without breaking the streaming (I thought about playlist with file1.avi- file10.avi, which all are symlinks, so when i’m sure, that file2 is playing, I can change symlink for file1 -but maybe there is something beter ?
  2ns : I want to add logo, and news ticker - adding logo is quite easy, but ticker looks hard : for now i know, that I have to use transcode sfilter, something like

  cvlc  --sout-keep --loop --sout '#transcode{soverlay, sfilter=marq{marquee="$N$_$T$_$D", position=5, size=14, opacity=255}, vb=600, vcodec=h264, venc=x264{bpyramid=none, weightp=0}}:standard{access=http,mux=ts,dst=:2000}' film.mp4

  but the problem is that ticker doesn’t move - it changes, but not move

  And I think if I can add logo twice - with ticker between logos - i think about layers :
  1. movie
  2. ticker background
  3. ticker text
  4. ticker frame (because i don’t want to scroll text from border to border)

  Any ideas ?