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• Why duration of the mp4 file created with ffmpeg from png files is smaller than expected ?

  17 août 2021, par qwark97

  I'm trying to concatenate a bunch of png files into one mp4 file using ffmpeg. I use following command :

  


  ffmpeg -f concat -i concat.txt -f mp4 out.mp4


  


  The "description file" (concat.txt) looks like this :

  


  file screen_001.png
duration 0.14538311958312988
file screen_002.png
duration 0.11382007598876953
file screen_003.png
duration 2.543360710144043
...
file screen_036.png
duration 0.15303301811218262
file screen_037.png
duration 0.160630464553833
file screen_038.png
duration 3.2751874923706055


  


  Given command works, I'm able to create desired mp4 file. The problem is, the duration of the output file is smaller than sum of the duration lines from concat.txt. I expect mp4 file 22.48s long but I get 19.20s long file.

  


  What am I doing wrong ? Maybe I'm not using some flag I should ? Is it even possible to do what I want ? I'm kind a newbie with ffmpeg and video manipulation at all so any help would be appreciated.

  


  Output of the ffmpeg, maybe will be useful :

  


  root@65181939e08e:/files/tmp# ffmpeg -f concat -i concat.txt -f mp4 out.mp4
ffmpeg version 4.1.6-1~deb10u1 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 8 (Debian 8.3.0-6)
  configuration: --prefix=/usr --extra-version='1~deb10u1' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Input #0, concat, from 'concat.txt':
  Duration: 00:00:22.48, start: 0.000000, bitrate: 0 kb/s
    Stream #0:0: Video: png, rgba(pc), 1366x768, 25 tbr, 25 tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (png (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0x5651f1a6e8c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x5651f1a6e8c0] profile High 4:4:4 Predictive, level 3.2, 4:4:4 8-bit
[libx264 @ 0x5651f1a6e8c0] 264 - core 155 r2917 0a84d98 - H.264/MPEG-4 AVC codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x1:0x111 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=4 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
Output #0, mp4, to 'out.mp4':
  Metadata:
    encoder         : Lavf58.20.100
    Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv444p, 1366x768, q=-1--1, 25 fps, 12800 tbn, 25 tbc
    Metadata:
      encoder         : Lavc58.35.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
frame=  483 fps=199 q=-1.0 Lsize=     258kB time=00:00:19.20 bitrate= 110.2kbits/s dup=445 drop=0 speed=7.89x    
video:252kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 2.564829%
[libx264 @ 0x5651f1a6e8c0] frame I:5     Avg QP: 7.86  size: 28761
[libx264 @ 0x5651f1a6e8c0] frame P:121   Avg QP:14.58  size:   729
[libx264 @ 0x5651f1a6e8c0] frame B:357   Avg QP:13.34  size:    70
[libx264 @ 0x5651f1a6e8c0] consecutive B-frames:  1.2%  0.0%  1.9% 96.9%
[libx264 @ 0x5651f1a6e8c0] mb I  I16..4: 88.2%  0.0% 11.8%
[libx264 @ 0x5651f1a6e8c0] mb P  I16..4:  1.3%  0.0%  0.3%  P16..4:  0.2%  0.0%  0.0%  0.0%  0.0%    skip:98.1%
[libx264 @ 0x5651f1a6e8c0] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8:  0.9%  0.0%  0.0%  direct: 0.0%  skip:99.1%  L0:59.4% L1:40.6% BI: 0.0%
[libx264 @ 0x5651f1a6e8c0] coded y,u,v intra: 7.9% 0.7% 1.3% inter: 0.0% 0.0% 0.0%
[libx264 @ 0x5651f1a6e8c0] i16 v,h,dc,p: 81% 18%  1%  0%
[libx264 @ 0x5651f1a6e8c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 33% 28% 22%  2%  3%  3%  3%  3%  3%
[libx264 @ 0x5651f1a6e8c0] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x5651f1a6e8c0] ref P L0: 72.5% 11.9% 12.4%  3.1%
[libx264 @ 0x5651f1a6e8c0] ref B L0: 50.4% 48.1%  1.4%
[libx264 @ 0x5651f1a6e8c0] ref B L1: 98.9%  1.1%
[libx264 @ 0x5651f1a6e8c0] kb/s:106.45


  


  Thanks for your help !