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• How to trim a file with FFMpeg programmatically ? (libavformat, avutils, ...)

  5 février 2016, par user361526

  I’m building an iOS app where re-encoding and trimming a video in the background is necessary.

  I can not use iOS libraries (AVFoundation) since they rely on the GPU and no app can access the GPU if it’s backgrounded.

  Due to this issue I switched to FFMpeg and compiled it (alongside libx264) and integrated it on my iOS app.

  To sum things up what I need is :

  1. Trim the video for the first 10 seconds
  2. re-scale the video

  After a couple of weeks - and banging my head against the wall quite often - I managed to :

  • split the video container into streams (demuxing)
  • copy the audio stream into the output stream (no decoding or encoding)
  • decode the video stream, run the necessary filters per frame, encode each resulting frame and remux it to the output stream (I decode the h264, filter it, re-encode it back to h264)

  If I were to run ffmpeg through the command line I would run it like this :

  ffmpeg -i input.MOV -ss 0 -t 10  -vf scale=320:240 -c:v libx264 -preset ultrafast -c:a copy output.mkv

  My concern is how to trim the video ? Although I could count the number of video frames that I encode/decode and based on the FPS decide when to stop I cannot do the same with the audio since I’m only demuxing and remuxing it.

  Ideally - before scaling the video - I would run a process to trim the video by copying the 10 seconds of each stream (video and audio) into a new video container.

  How to I achieve this through the AV libraries ?

• Exactly what is ` /dev/null ` when read is done by null ? [duplicate]

  26 décembre 2015, par Faron

  This question already has an answer here :

  • What is null in bash ?
    
    4 answers
    

  '> /dev/null' is very common syntax and that’s something that is not a new concept ; but, I have came to this scripting and couldn’t figure the logic behind '< /dev/null' especially with FFMpeg.

  I wrote dozens of scripts that handles FFMpeg, and I found that in order for script itself to successfully call and execute FFMpeg on its own, adding ’< /dev/null’ at end of command line of ffmpeg. For example :

  ffmpeg -i $INPUT -c:v copy -c:a copy output.mp4 < /dev/null

  But if I didn’t add that sytnax at end of the command, script couldn’t "push" the execution over to FFMpeg. I understood the whole concept when it comes to "write" as > for all null, stdout, stdin, but... read by null ? scratching on head

  So, what is < /dev/null exactly ?

• ffmpeg failing to expand drawtext

  26 novembre 2015, par charlie80

  I am trying to overlay a seconds:milliseconds timestamp on my video, but I have been breaking my head over this for some hours without any result. If I write :

  ffmpeg -f lavfi -i testsrc=duration=5:size=800x600:rate=30 -vf drawtext="fontfile=C\\:/Windows/Fonts/arial.ttf:text='%{pts}': x=(w-tw)/2: y=h-(2*lh): fontcolor=white: box=1: boxcolor=0x00000000@1" -preset ultrafast output.mp4

  the %{pts} does not get expanded, and only shows the literal text {pts} on the frame.

  Please note that I have read a ton of guides around the web (ffmpeg docs/guides/wikis, stackoverflow, blogs, etc.) on this timestamp overlay stuff, but none of the solutions/syntaxes work : it simply overlays the literal text.

  Some context :

  • using Windows 7x64 and TCC/LE
  • ffmpeg Zeranoe build version git-12a419d (2015-11-23)

  The full output log :

  [E:\]ffmpeg -f lavfi -i testsrc=duration=5:size=800x600:rate=30 -vf drawtext="fontfile=C\\:/Windows/Fonts/arial.ttf:text=%{pts}: x=(w-tw)/2: y=h-(2*lh): fontcolor=white: box=1: boxcolor=0x00000000@1" -preset ultrafast output.mp4
  
  ffmpeg version N-76822-g12a419d Copyright (c) 2000-2015 the FFmpeg developers
  
    built with gcc 5.2.0 (GCC)
  
    configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzimg --enable-lzma --enable-decklink --enable-zlib
  
    libavutil      55.  9.100 / 55.  9.100
  
    libavcodec     57. 16.100 / 57. 16.100
  
    libavformat    57. 19.100 / 57. 19.100
  
    libavdevice    57.  0.100 / 57.  0.100
  
    libavfilter     6. 15.100 /  6. 15.100
  
    libswscale      4.  0.100 /  4.  0.100
  
    libswresample   2.  0.101 /  2.  0.101
  
    libpostproc    54.  0.100 / 54.  0.100
  
  Input #0, lavfi, from 'testsrc=duration=5:size=800x600:rate=30':
  
    Duration: N/A, start: 0.000000, bitrate: N/A
  
      Stream #0:0: Video: rawvideo (RGB[24] / 0x18424752), rgb24, 800x600 [SAR 1:1 DAR 4:3], 30 tbr, 30 tbn, 30 tbc
  
  File 'output.mp4' already exists. Overwrite ? [y/N] y
  
  No pixel format specified, yuv444p for H.264 encoding chosen.
  
  Use -pix_fmt yuv420p for compatibility with outdated media players.
  
  [libx264 @ 00000000003f83c0] using SAR=1/1
  
  [libx264 @ 00000000003f83c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 Cache64 SlowShuffle
  
  [libx264 @ 00000000003f83c0] profile High 4:4:4 Predictive, level 3.1, 4:4:4 8-bit
  
  [libx264 @ 00000000003f83c0] 264 - core 148 r2638 7599210 - H.264/MPEG-4 AVC codec - Copyleft 2003-2015 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=6 threads=3 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=250 keyint_min=25 scenecut=0 intra_refresh=0 rc=crf mbtree=0 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=0
  
  Output #0, mp4, to 'output.mp4':
  
    Metadata:
  
      encoder         : Lavf57.19.100
  
      Stream #0:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv444p, 800x600 [SAR 1:1 DAR 4:3], q=-1--1, 30 fps, 15360 tbn, 30 tbc
  
      Metadata:
  
        encoder         : Lavc57.16.100 libx264
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
  
  Press [q] to stop, [?] for help
  
  frame=  150 fps= 61 q=-1.0 Lsize=     185kB time=00:00:05.00 bitrate= 303.2kbits/s
  
  video:184kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.755086%
  
  [libx264 @ 00000000003f83c0] frame I:1     Avg QP:20.00  size: 18409
  
  [libx264 @ 00000000003f83c0] frame P:149   Avg QP:16.11  size:  1135
  
  [libx264 @ 00000000003f83c0] mb I  I16..4: 100.0%  0.0%  0.0%
  
  [libx264 @ 00000000003f83c0] mb P  I16..4:  0.7%  0.0%  0.0%  P16..4:  5.1%  0.0%  0.0%  0.0%  0.0%    skip:94.2%
  
  [libx264 @ 00000000003f83c0] coded y,u,v intra: 5.0% 3.3% 2.8% inter: 1.1% 1.0% 0.9%
  
  [libx264 @ 00000000003f83c0] i16 v,h,dc,p: 81%  6%  2% 11%
  
  [libx264 @ 00000000003f83c0] kb/s:299.93
  
  
  
  [E:\]