[FFmpeg-user] x-axis range of drawgraph picture mode

[Dave Rice]

Hi ffmpeg-user,

I’m using drawgraph with slide=picture in order to make some still images of audiovisual metrics upon a timeline. I’d like to use drawgraph and drawtext in order to overlay some x-axis markers and label the timeline; however I’m unclear how the x-axis is represented in this mode. For instance, the example below plots lavfi.astats.1.Min_level for a 60 second sample, but the resulting image appears to have a x-axis that represents more than 60 seconds. The result appears to roughly plot about 80 seconds with the 60-80 second range being blank. 

ffmpeg -f lavfi -i "aevalsrc=d=60:exprs=sin(PI*t):s=48000,aformat=sample_fmts=dbl,astats=metadata=1:reset=1,adrawgraph=m1=lavfi.astats.1.Min_level:max=1:min=-1:slide=picture:s=1920x240" -y test.png

Is there some math that I can use to determine the maximum value of the x-axis from the plotted image?

Full output:

ffmpeg -f lavfi -i "aevalsrc=d=60:exprs=sin(PI*t):s=48000,aformat=sample_fmts=dbl,astats=metadata=1:reset=1,adrawgraph=m1=lavfi.astats.1.Min_level:max=1:min=-1:slide=picture:s=1920x240" -y test.png
ffmpeg version N-51550-g41d7c4d381 Copyright (c) 2000-2018 the FFmpeg developers
  built with Apple LLVM version 9.0.0 (clang-900.0.38)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/HEAD-41d7c4d --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-gpl --enable-ffplay --enable-libfreetype --enable-libmp3lame --enable-libx264 --enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma
  libavutil      56.  9.100 / 56.  9.100
  libavcodec     58. 14.100 / 58. 14.100
  libavformat    58. 10.100 / 58. 10.100
  libavdevice    58.  2.100 / 58.  2.100
  libavfilter     7. 13.100 /  7. 13.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  0.102 /  5.  0.102
  libswresample   3.  0.101 /  3.  0.101
  libpostproc    55.  0.100 / 55.  0.100
[Parsed_aevalsrc_0 @ 0x7f8035500000] EOF timestamp not reliable
Input #0, lavfi, from 'aevalsrc=d=60:exprs=sin(PI*t):s=48000,aformat=sample_fmts=dbl,astats=metadata=1:reset=1,adrawgraph=m1=lavfi.astats.1.Min_level:max=1:min=-1:slide=picture:s=1920x240':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: rawvideo (RGBA / 0x41424752), rgba, 1920x240 [SAR 1:1 DAR 8:1], 48k tbr, 48k tbn, 48k tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> png (native))
Press [q] to stop, [?] for help
[image2 @ 0x7f8036801400] Frame rate very high for a muxer not efficiently supporting it.
Please consider specifying a lower framerate, a different muxer or -vsync 2
Output #0, image2, to 'test.png':
  Metadata:
    encoder         : Lavf58.10.100
    Stream #0:0: Video: png, rgba, 1920x240 [SAR 1:1 DAR 8:1], q=2-31, 200 kb/s, 48k fps, 48k tbn, 48k tbc
    Metadata:
      encoder         : Lavc58.14.100 png
frame=    1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.00 bitrate=N/A speed=0.00116x    
video:14kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[Parsed_astats_2 @ 0x7f8035500640] Channel: 1
[Parsed_astats_2 @ 0x7f8035500640] DC offset: -0.016786
[Parsed_astats_2 @ 0x7f8035500640] Min level: -0.033504
[Parsed_astats_2 @ 0x7f8035500640] Max level: 0.000000
[Parsed_astats_2 @ 0x7f8035500640] Min difference: 0.000065
[Parsed_astats_2 @ 0x7f8035500640] Max difference: 0.000065
[Parsed_astats_2 @ 0x7f8035500640] Mean difference: 0.000066
[Parsed_astats_2 @ 0x7f8035500640] RMS difference: 0.000066
[Parsed_astats_2 @ 0x7f8035500640] Peak level dB: -29.498054
[Parsed_astats_2 @ 0x7f8035500640] RMS level dB: -34.255905
[Parsed_astats_2 @ 0x7f8035500640] RMS peak dB: -34.255905
[Parsed_astats_2 @ 0x7f8035500640] RMS trough dB: -34.255905
[Parsed_astats_2 @ 0x7f8035500640] Crest factor: 1.729388
[Parsed_astats_2 @ 0x7f8035500640] Flat factor: 0.000000
[Parsed_astats_2 @ 0x7f8035500640] Peak count: 1
[Parsed_astats_2 @ 0x7f8035500640] Bit depth: 59/64
[Parsed_astats_2 @ 0x7f8035500640] Dynamic range: 60.204373
[Parsed_astats_2 @ 0x7f8035500640] Overall
[Parsed_astats_2 @ 0x7f8035500640] DC offset: -0.016786
[Parsed_astats_2 @ 0x7f8035500640] Min level: -0.033504
[Parsed_astats_2 @ 0x7f8035500640] Max level: 0.000000
[Parsed_astats_2 @ 0x7f8035500640] Min difference: 0.000065
[Parsed_astats_2 @ 0x7f8035500640] Max difference: 0.000065
[Parsed_astats_2 @ 0x7f8035500640] Mean difference: 0.000066
[Parsed_astats_2 @ 0x7f8035500640] RMS difference: 0.000066
[Parsed_astats_2 @ 0x7f8035500640] Peak level dB: -29.498054
[Parsed_astats_2 @ 0x7f8035500640] RMS level dB: -34.255905
[Parsed_astats_2 @ 0x7f8035500640] RMS peak dB: -34.255905
[Parsed_astats_2 @ 0x7f8035500640] RMS trough dB: -34.255905
[Parsed_astats_2 @ 0x7f8035500640] Flat factor: 0.000000
[Parsed_astats_2 @ 0x7f8035500640] Peak count: 1.000000
[Parsed_astats_2 @ 0x7f8035500640] Bit depth: 59/64
[Parsed_astats_2 @ 0x7f8035500640] Number of samples: 512

Best Regards,

Dave Rice