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• libavutil : Always use some GCC style attributes on clang

  18 juillet 2016, par Martin Storsjö

  libavutil : Always use some GCC style attributes on clang
  Clang normally disguises as GCC (defining __GNUC__), and thus get
  
  all the normal GCC specific attributes.
  Clang can also work as a drop-in replacement for MSVC, and in these
  
  cases, it doesn’t define __GNUC__, but defines _MSC_VER instead.
  Even in these setups, it still supports the GCC style attributes,
  
  thus use them, especially where there isn’t any MSVC specific
  
  version, or where the MSVC specific version doesn’t work on clang
  
  (for DECLARE_ASM_CONST).
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavutil/attributes.h
  • [DBH] libavutil/mem.h

• FFmpeg, videotoolbox and avplayer in iOS

  9 janvier 2017, par Hwangho Kim

  I have a question how these things are connected and what they exactly do.

  FYI, I have a few experience about video player and encoding and decoding.

  In my job I deal udp streaming from server and take it with ffmpeg and decodes it and draw it with openGL. And also using ffmpeg for video player.

  These are the questions...

  1. Only ffmpeg can decodes UDP streaming (encoded with ffmpeg from the server) or not ?

  I found some useful information about videotoolbox which can decode streaming with hardware acceleration in iOS. so could I also decode the streaming from the server with videotoolbox ?

  2. If it is possible to decode with videotoolbox (I mean if the videotoolbox could be the replacement for ffmpeg), then what is the videotoolbox source code in ffmpeg ? why it is there ?

  In my decoder I make AVCodecContext from the streaming and it has hwaccel and hwaccel_context field which set null both of them. I thought this videotoolbox is kind of API which can help ffmpeg to use hwaccel of iOS. But it looks not true for now...

  3. If videotoolbox can decode streaming, Does this also decode for H264 in local ? or only streaming possible ?

  AVPlayer is a good tool to play a video but if videotoolbox could replace this AVPlayer then, what’s the benefit ? or impossible ?

  4. FFmpeg only uses CPU for decoding (software decoder) or hwaccel also ?

  When I play a video with ffmpeg player, CPU usage over 100% and Does it means this ffmpeg uses only software decoder ? or there is a way to use hwaccel ?

  Please understand my poor english and any answer would be appreciated.

  Thanks.

• ffmpeg mp4 upload to Twitter - Unsupported Error

  13 juin 2016, par Noitidart

  I have created a screencast, it was saved as webm. Using ffmpeg I converted it to a mp4 :

  That kind of file isn’t supported yet. Try uploading a gif, video, or picture instead.

  ffmpeg -f input.webm -pix_fmt yuv420p -strict -2 output.mp4

  I use yuv420p as that is what this topic says for twitter - https://twittercommunity.com/t/unable-to-upload-video-to-twitter/61721/3

  However when I open a new tab, go to twitter, click the photo icon, clicking upload instantly gives me error "That kind of file isn’t supported yet. Try uploading a gif, video, or picture instead.". It cant check the pix format that fast. Anyonek now what can be going on here ?

  Here is ffmpeg console output :

  ffmpeg version 2.2.1 Copyright (c) 2000-2014 the FFmpeg developers
  
    built on Jun  9 2014 20:01:41 with emcc (Emscripten GCC-like replacement) 1.12.0 (commit 6960d2296299e96d43e694806f5d35799ef8d39c)
  
    configuration: --cc=emcc --prefix=/Users/bgrinstead/Sites/videoconverter.js/build/ffmpeg/../dist --enable-cross-compile --target-os=none --arch=x86_32 --cpu=generic --disable-ffplay --disable-ffprobe --disable-ffserver --disable-asm --disable-doc --disable-devices --disable-pthreads --disable-w32threads --disable-network --disable-hwaccels --disable-parsers --disable-bsfs --disable-debug --disable-protocols --disable-indevs --disable-outdevs --enable-protocol=file
  
    libavutil      52. 66.100 / 52. 66.100
  
    libavcodec     55. 52.102 / 55. 52.102
  
    libavformat    55. 33.100 / 55. 33.100
  
    libavdevice    55. 10.100 / 55. 10.100
  
    libavfilter     4.  2.100 /  4.  2.100
  
    libswscale      2.  5.102 /  2.  5.102
  
    libswresample   0. 18.100 /  0. 18.100
  
  [vp8 @ 0xdde410] Warning: not compiled with thread support, using thread emulation
  
  Input #0, matroska,webm, from 'input.webm':
  
    Metadata:
  
      encoder         : QTmuxingAppLibWebM-0.0.1
  
    Duration: N/A, start: 0.000000, bitrate: N/A
  
      Stream #0:0(eng): Video: vp8, yuv420p, 1920x1200, SAR 1:1 DAR 8:5, 30 fps, 30 tbr, 1k tbn, 1k tbc (default)
  
  Incompatible pixel format 'yuv420p' for codec 'gif', auto-selecting format 'pal8'
  
  [swscaler @ 0xdd7f40] No accelerated colorspace conversion found from yuv420p to bgr8.
  
  [gif @ 0xde5290] Warning: not compiled with thread support, using thread emulation
  
  [vp8 @ 0xdde410] Warning: not compiled with thread support, using thread emulation
  
  Output #0, gif, to 'output/output.gif':
  
    Metadata:
  
      encoder         : Lavf55.33.100
  
      Stream #0:0(eng): Video: gif, pal8, 1920x1200 [SAR 1:1 DAR 8:5], q=2-31, 200 kb/s, 100 tbn, 30 tbc (default)
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (vp8 -> gif)
  
  Press [q] to stop, [?] for help
  
  frame=    1 fps=0.0 q=0.0 size=       0kB time=00:00:00.03 bitrate=   8.5kbits/s    
  
  frame=    6 fps=0.0 q=0.0 size=     640kB time=00:00:00.33 bitrate=15877.0kbits/s    
  
  frame=   12 fps= 11 q=0.0 size=    1452kB time=00:00:00.63 bitrate=18878.9kbits/s    
  
  frame=   17 fps= 10 q=0.0 size=    2080kB time=00:00:00.91 bitrate=18723.7kbits/s    
  
  frame=   22 fps=9.6 q=0.0 size=    2698kB time=00:00:01.16 bitrate=19052.0kbits/s    
  
  frame=   27 fps=9.7 q=0.0 size=    3294kB time=00:00:01.43 bitrate=18869.4kbits/s    
  
  frame=   33 fps=9.6 q=0.0 size=    4001kB time=00:00:01.76 bitrate=18622.0kbits/s    
  
  frame=   38 fps=9.5 q=0.0 size=    4567kB time=00:00:02.04 bitrate=18339.7kbits/s    
  
  frame=   44 fps=9.5 q=0.0 size=    5236kB time=00:00:02.37 bitrate=18097.4kbits/s    
  
  frame=   50 fps=9.7 q=0.0 size=    5902kB time=00:00:02.71 bitrate=17839.9kbits/s    
  
  frame=   55 fps=9.6 q=0.0 size=    6457kB time=00:00:02.96 bitrate=17868.9kbits/s    
  
  frame=   55 fps=9.6 q=0.0 Lsize=    6567kB time=00:00:02.96 bitrate=18175.9kbits/s    
  
  video:6623kB audio:0kB subtitle:0 data:0 global headers:0kB muxing overhead -0.834044%

  Here is a screenshot :