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• FFMPEG - adding a nullsrc causes my script to report "1000 duplicate frames"

  14 juin 2020, par rossmcm

  I'm trying to add coloured rectangle highlights to a video, appearing at different locations and times. The highlights are on a 6x6 grid of 320x180 rectangles.

  



  Originally I didn't have the nullsrc=size=1920x1080 thinking that it would start with an empty image, but it seems that that causes it to make assumptions about where the input is coming from. So I added the nullsrc=size=1920x1080 to start with a transparent 1920x1080 image but this command returns a warning that 1000 duplicate frames have been produced and it keeps going past the end of the input video with no signs of stopping.

  



  ffmpeg -y \       
  -i "Input.mp4" \           
  -filter_complex \ 
 "nullsrc=size=1920x1080, drawbox=x=(3-1)*320:y=(3-1)*180:w=320:h=180:t=7:c=cyan,   fade=in:st=10:d=1:alpha=1, fade=out:st=40:d=1:alpha=1[tmp1]; \
  nullsrc=size=1920x1080, drawbox=x=(4-1)*320:y=(4-1)*180:w=320:h=180:t=7:c=blue,   fade=in:st=20:d=1:alpha=1, fade=out:st=50:d=1:alpha=1[tmp2]; \
  nullsrc=size=1920x1080, drawbox=x=(5-1)*320:y=(5-1)*180:w=320:h=180:t=7:c=green,  fade=in:st=30:d=1:alpha=1, fade=out:st=60:d=1:alpha=1[tmp3]; \
  nullsrc=size=1920x1080, drawbox=x=(6-1)*320:y=(6-1)*180:w=320:h=180:t=7:c=yellow, fade=in:st=40:d=1:alpha=1, fade=out:st=70:d=1:alpha=1[tmp4]; \
  [tmp1][tmp2] overlay=0:0[ovr1]; \ 
  [tmp3][tmp4] overlay=0:0[ovr2]; \ 
  [ovr1][ovr2] overlay=0:0[boxes]; \ 
  [0:v][boxes] overlay=0:0" \        
  "Output.mp4"


  



  The input video is around 01:45 long. Log of run :

  



  ffmpeg -y        -loglevel verbose       -i "Input.mp4"          -filter_complex " nullsrc=size=1920x1080, drawbox=x=(3-1)*320:y=(3-1)*180:w=320:h=180:t=7:c=cyan,   fade=in:st=10:d=1:alpha=1, fade=out:st=40:d=1:alpha=1[tmp1]; nullsrc=size=1920x1080, drawbox=x  =(4-1)*320:y=(4-1)*180:w=320:h=180:t=7:c=blue,   fade=in:st=20:d=1:alpha=1, fade=out:st=50:d=1:alpha=1[tmp2]; nullsrc=size=1920x1080, drawbox=x=(5-1)*320:y=(5-1)*180:w=320:h=180:t=7:c=green,  fa
de=in:st=30:d=1:alpha=1, fade=out:st=60:d=1:alpha=1[tmp3]; nullsrc=size=1920x1080, drawbox=x=(6-1)*320:y=(6-1)*180:w=320:h=180:t=7:c=yellow, fade=in:st=40:d=1:alpha=1, fade=out:st=70:d=1:alpha=1[tmp4]; [tmp1][tmp2] overlay=0:0[ovr1]; [tmp3][tmp4] overlay=0:0[ovr2]; [ovr1][ovr2] overlay=0:0[boxes]; [0:v][boxes] overlay=0:0"      "Output.mp4"
ffmpeg version 3.4 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 7.2.0 (GCC)
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-bzlib --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvid
stab --enable-libvorbis --enable-cuda --enable-cuvid --enable-d3d11va --enable-nvenc --enable-dxva2 --enable-avisynth --enable-libmfx
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
[h264 @ 000001df2b623ea0] Reinit context to 1920x1088, pix_fmt: yuv420p
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Input.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:01:48.67, start: 0.000000, bitrate: 1825 kb/s
    Stream #0:0(und): Video: h264 (High), 1 reference frame (avc1 / 0x31637661), yuv420p(left), 1920x1080 (1920x1088) [SAR 1:1 DAR 16:9], 1693 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: mp3 (mp4a / 0x6134706D), 44100 Hz, stereo, s16p, 127 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
[Parsed_nullsrc_0 @ 000001df2b61af00] size:1920x1080 rate:25/1 duration:-1.000000 sar:1/1
[Parsed_fade_2 @ 000001df2b6a6860] type:in start_time:10.000000 duration:1.000000 alpha:1
[Parsed_fade_3 @ 000001df2b9ddec0] type:out start_time:40.000000 duration:1.000000 alpha:1
[Parsed_nullsrc_4 @ 000001df2bc00560] size:1920x1080 rate:25/1 duration:-1.000000 sar:1/1
[Parsed_fade_6 @ 000001df29fe6780] type:in start_time:20.000000 duration:1.000000 alpha:1
[Parsed_fade_7 @ 000001df29fe6840] type:out start_time:50.000000 duration:1.000000 alpha:1
[Parsed_nullsrc_8 @ 000001df2b642dc0] size:1920x1080 rate:25/1 duration:-1.000000 sar:1/1
[Parsed_fade_10 @ 000001df2b6442a0] type:in start_time:30.000000 duration:1.000000 alpha:1
[Parsed_fade_11 @ 000001df2b6444e0] type:out start_time:60.000000 duration:1.000000 alpha:1
[Parsed_nullsrc_12 @ 000001df2b62d000] size:1920x1080 rate:25/1 duration:-1.000000 sar:1/1
[Parsed_fade_14 @ 000001df2b62d580] type:in start_time:40.000000 duration:1.000000 alpha:1
[Parsed_fade_15 @ 000001df2b62ddc0] type:out start_time:70.000000 duration:1.000000 alpha:1
Stream mapping:
  Stream #0:0 (h264) -> overlay:main (graph 0)
  overlay (graph 0) -> Stream #0:0 (libx264)
  Stream #0:1 -> #0:1 (mp3 (native) -> aac (native))
Press [q] to stop, [?] for help
[h264 @ 000001df2b8e5040] Reinit context to 1920x1088, pix_fmt: yuv420p
[graph_1_in_0_1 @ 000001df2b62e100] tb:1/44100 samplefmt:s16p samplerate:44100 chlayout:0x3
[format_out_0_1 @ 000001df2b62e5e0] auto-inserting filter 'auto_resampler_0' between the filter 'Parsed_anull_0' and the filter 'format_out_0_1'
[auto_resampler_0 @ 000001df2b62dd00] ch:2 chl:stereo fmt:s16p r:44100Hz -> ch:2 chl:stereo fmt:fltp r:44100Hz
[Parsed_nullsrc_0 @ 000001df2b62e440] size:1920x1080 rate:25/1 duration:-1.000000 sar:1/1
[Parsed_fade_2 @ 000001df2b62df60] type:in start_time:10.000000 duration:1.000000 alpha:1
[Parsed_fade_3 @ 000001df2b62e6c0] type:out start_time:40.000000 duration:1.000000 alpha:1
[Parsed_nullsrc_4 @ 000001df2b62d9c0] size:1920x1080 rate:25/1 duration:-1.000000 sar:1/1
[Parsed_fade_6 @ 000001df2b62e520] type:in start_time:20.000000 duration:1.000000 alpha:1
[Parsed_fade_7 @ 000001df2b62d8e0] type:out start_time:50.000000 duration:1.000000 alpha:1
[Parsed_nullsrc_8 @ 000001df2b62e1e0] size:1920x1080 rate:25/1 duration:-1.000000 sar:1/1
[Parsed_fade_10 @ 000001df2b62e2a0] type:in start_time:30.000000 duration:1.000000 alpha:1
[Parsed_fade_11 @ 000001df2b62e380] type:out start_time:60.000000 duration:1.000000 alpha:1
[Parsed_nullsrc_12 @ 000001df2b62dc20] size:1920x1080 rate:25/1 duration:-1.000000 sar:1/1
[Parsed_fade_14 @ 000001df2b816f60] type:in start_time:40.000000 duration:1.000000 alpha:1
[Parsed_fade_15 @ 000001df2b817ac0] type:out start_time:70.000000 duration:1.000000 alpha:1
[graph 0 input from stream 0:0 @ 000001df2b817ba0] w:1920 h:1080 pixfmt:yuv420p tb:1/15360 fr:30/1 sar:1/1 sws_param:flags=2
[Parsed_drawbox_1 @ 000001df2b62da80] x:640 y:360 w:320 h:180 color:0xA9A610FF
[Parsed_drawbox_5 @ 000001df2b62e780] x:960 y:540 w:320 h:180 color:0x29F06EFF
[Parsed_overlay_16 @ 000001df2b817860] main w:1920 h:1080 fmt:yuva420p overlay w:1920 h:1080 fmt:yuva420p
[Parsed_overlay_16 @ 000001df2b817860] [framesync @ 000001df2b815348] Selected 1/25 time base
[Parsed_overlay_16 @ 000001df2b817860] [framesync @ 000001df2b815348] Sync level 2
[Parsed_drawbox_9 @ 000001df2b62db60] x:1280 y:720 w:320 h:180 color:0x515B51FF
[Parsed_drawbox_13 @ 000001df2b818be0] x:1600 y:900 w:320 h:180 color:0xD21092FF
[Parsed_overlay_17 @ 000001df2b816d00] main w:1920 h:1080 fmt:yuva420p overlay w:1920 h:1080 fmt:yuva420p
[Parsed_overlay_17 @ 000001df2b816d00] [framesync @ 000001df2b815e48] Selected 1/25 time base
[Parsed_overlay_17 @ 000001df2b816d00] [framesync @ 000001df2b815e48] Sync level 2
[Parsed_overlay_18 @ 000001df2b8183c0] main w:1920 h:1080 fmt:yuva420p overlay w:1920 h:1080 fmt:yuva420p
[Parsed_overlay_18 @ 000001df2b8183c0] [framesync @ 000001df2b815668] Selected 1/25 time base
[Parsed_overlay_18 @ 000001df2b8183c0] [framesync @ 000001df2b815668] Sync level 2
[Parsed_overlay_19 @ 000001df2b817d40] main w:1920 h:1080 fmt:yuv420p overlay w:1920 h:1080 fmt:yuva420p
[Parsed_overlay_19 @ 000001df2b817d40] [framesync @ 000001df2b816488] Selected 1/76800 time base
[Parsed_overlay_19 @ 000001df2b817d40] [framesync @ 000001df2b816488] Sync level 2
[libx264 @ 000001df2b62cd40] using SAR=1/1
[libx264 @ 000001df2b62cd40] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 000001df2b62cd40] profile High, level 4.0
[libx264 @ 000001df2b62cd40] 264 - core 152 r2851 ba24899 - H.264/MPEG-4 AVC codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 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 weigh
tb=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 'Output.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf57.83.100
    Stream #0:0: Video: h264 (libx264), 1 reference frame (avc1 / 0x31637661), yuv420p(left), 1920x1080 [SAR 1:1 DAR 16:9], q=-1--1, 30 fps, 15360 tbn, 30 tbc (default)
    Metadata:
      encoder         : Lavc57.107.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, delay 1024, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      encoder         : Lavc57.107.100 aac
[Parsed_overlay_19 @ 000001df2b817d40] [framesync @ 000001df2b816488] Sync level 1speed=0.78x
Past duration 0.800774 too large
*** 1 dup!5 fps= 24 q=29.0 size=   21760kB time=00:01:46.86 bitrate=1668.0kbits/s speed=0.78x
    Last message repeated 1 times
*** 1 dup!8 fps= 24 q=29.0 size=   21760kB time=00:01:47.30 bitrate=1661.3kbits/s dup=2 drop=0 speed=0.78x
    Last message repeated 2 times
*** 1 dup!3 fps= 24 q=29.0 size=   21760kB time=00:01:47.80 bitrate=1653.6kbits/s dup=5 drop=0 speed=0.781x
    Last message repeated 1 times

...

    Last message repeated 2 times
*** 1 dup!3 fps= 25 q=29.0 size=   27392kB time=00:05:05.80 bitrate= 733.8kbits/s dup=995 drop=0 speed=0.832x
    Last message repeated 1 times
*** 1 dup!6 fps= 25 q=29.0 size=   27392kB time=00:05:06.23 bitrate= 732.8kbits/s dup=997 drop=0 speed=0.832x
    Last message repeated 1 times
*** 1 dup!0 fps= 25 q=29.0 size=   27392kB time=00:05:06.70 bitrate= 731.6kbits/s dup=999 drop=0 speed=0.832x
    Last message repeated 1 times
More than 1000 frames duplicated
*** 1 dup!3 fps= 25 q=29.0 size=   27392kB time=00:05:07.13 bitrate= 730.6kbits/s dup=1001 drop=0 speed=0.832x
    Last message repeated 2 times
*** 1 dup!8 fps= 25 q=29.0 size=   27392kB time=00:05:07.63 bitrate= 729.4kbits/s dup=1004 drop=0 speed=0.832x
    Last message repeated 1 times
... 
*** 1 dup!9 fps= 25 q=29.0 size=   27904kB time=00:05:18.66 bitrate= 717.3kbits/s dup=1059 drop=0 speed=0.834x
    Last message repeated 1 times
*** 1 dup!3 fps= 25 q=29.0 size=   27904kB time=00:05:19.13 bitrate= 716.3kbits/s dup=1061 drop=0 speed=0.834x
frame= 9635 fps= 25 q=-1.0 Lsize=   28364kB time=00:05:21.06 bitrate= 723.7kbits/s dup=1062 drop=0 speed=0.837x
video:26539kB audio:1637kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.669889%
Input file #0 (Input.mp4):
  Input stream #0:0 (video): 3260 packets read (23006797 bytes); 3260 frames decoded;
  Input stream #0:1 (audio): 4025 packets read (1682285 bytes); 4025 frames decoded (4636800 samples);
  Total: 7285 packets (24689082 bytes) demuxed
Output file #0 (Output.mp4):
  Output stream #0:0 (video): 9635 frames encoded; 9635 packets muxed (27175566 bytes);
  Output stream #0:1 (audio): 4529 frames encoded (4636800 samples); 4530 packets muxed (1676214 bytes);
  Total: 14165 packets (28851780 bytes) muxed
[libx264 @ 000001df2b62cd40] frame I:39    Avg QP:16.49  size:213954
[libx264 @ 000001df2b62cd40] frame P:2446  Avg QP:17.77  size:  6277
[libx264 @ 000001df2b62cd40] frame B:7150  Avg QP:30.38  size:   486
[libx264 @ 000001df2b62cd40] consecutive B-frames:  0.8%  0.8%  0.1% 98.3%
[libx264 @ 000001df2b62cd40] mb I  I16..4: 13.2% 43.0% 43.8%
[libx264 @ 000001df2b62cd40] mb P  I16..4:  0.2%  0.2%  0.1%  P16..4:  7.1%  3.3%  1.7%  0.0%  0.0%    skip:87.5%
[libx264 @ 000001df2b62cd40] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8:  4.3%  0.1%  0.0%  direct: 0.0%  skip:95.5%  L0:41.9% L1:56.1% BI: 2.0%
[libx264 @ 000001df2b62cd40] 8x8 transform intra:44.1% inter:65.8%
[libx264 @ 000001df2b62cd40] coded y,uvDC,uvAC intra: 71.3% 83.5% 52.5% inter: 1.1% 1.5% 0.0%
[libx264 @ 000001df2b62cd40] i16 v,h,dc,p: 31% 28%  4% 38%
[libx264 @ 000001df2b62cd40] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 28% 20% 10%  6%  6%  7%  7%  8%  8%
[libx264 @ 000001df2b62cd40] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 33% 28%  7%  4%  6%  6%  6%  5%  5%
[libx264 @ 000001df2b62cd40] i8c dc,h,v,p: 34% 27% 28% 11%
[libx264 @ 000001df2b62cd40] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 000001df2b62cd40] ref P L0: 71.1% 14.9% 10.6%  3.4%
[libx264 @ 000001df2b62cd40] ref B L0: 93.3%  5.9%  0.8%
[libx264 @ 000001df2b62cd40] ref B L1: 97.8%  2.2%
[libx264 @ 000001df2b62cd40] kb/s:676.90
[aac @ 000001df2b6a5620] Qavg: 1165.766
Exiting normally, received signal 2.
Terminate batch job (Y/N)? y


  


• FFMPEG Debug "Invalid data found when processing input"

  29 septembre 2020, par dgcipp

  How can I debug this error ? I am trying to display a vp8-encoded video stream (TCP) from Android (x86) to my PC but I got this message from ffplay : "tcp ://10.8.0.3:49152 ? listen : Invalid data found when processing input"

  


  With h264 it works and the same code in an android device works with vp8 too.

  


  Command in the server :

  


  ffplay -i tcp://10.8.0.3:49152?listen


  


  I have tried adding verbosity or log-level debug, but it shows the same. How can I get a detailed error ?

  


  

  


• "invalid argument" for av_buffersrc_write_frame / av_buffersrc_add_frame

  1er février 2017, par TheSHEEEP

  I am trying to use FFmpeg C api to create a filter to merge two audio streams. Trying to follow the code from here : Implementing a multiple input filter graph with the Libavfilter library in Android NDK

  Everything seems to be alright.

  However, as soon as I call av_buffersrc_write_frame (or av_buffersrc_add_frame or av_buffersrc_add_frame_flags, it doesn’t matter), FFmpeg just reports "invalid argument" and nothing else - an utterly useless error message, as it could mean everything.
  Which argument is invalid ? What is wrong about it ? Nobody knows.

  I am initializing the graph and "grabbing" the contexts of the buffer sources for later use like this :

  // Alloc filter graph
  
  *filter_graph = avfilter_graph_alloc();
  
  if ((*filter_graph) == NULL) {
  
      os::log("Error: Cannot allocate filter graph.");
  
      return AVERROR(ENOMEM);
  
  }
  
  
  
  // Building the filter string, ommitted
  
  
  
  int result = avfilter_graph_parse2(*filter_graph, filterString.c_str(), &gis, &gos, NULL);
  
  if (result < 0)
  
  {
  
      char errorBuf[1024];
  
      av_make_error_string(errorBuf, 1024, result);
  
      log("Error: Parsing filter string: %s", errorBuf);
  
      return AVERROR_EXIT;
  
  }
  
  
  
  // Configure the graph
  
  result = avfilter_graph_config(*filter_graph, NULL);
  
  if (result < 0)
  
  {
  
      char errorBuf[1024];
  
      av_make_error_string(errorBuf, 1024, result);
  
      log("Error: Configuring filter graph: %s", errorBuf);
  
      return AVERROR_EXIT;
  
  }
  
  
  
  // Get the buffer source and buffer sink contexts
  
  for (unsigned int i = 0; i < (*filter_graph)->nb_filters; ++i) {
  
      AVFilterContext* filterContext = (*filter_graph)->filters[i];
  
  
  
      // The first two filters should be the abuffers
  
      std::string name = filterContext->name;
  
      if (name.find("abuffer") != name.npos && i < 2) {
  
          inputs[i].buffer_source_context = filterContext;
  
      }
  
  
  
      // abuffersink is the one we need to get the converted frames from
  
      if (name.find("abuffersink") != name.npos) {
  
          *buffer_sink_context = filterContext;
  
      }
  
  }

  There are absolutely no errors in the initialization. At least FFmpeg has only this to say about it, which I think looks good :

  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] Setting 'time_base' to value '1/48000'
  
  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] Setting 'sample_rate' to value '48000'
  
  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] Setting 'sample_fmt' to value '1'
  
  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] Setting 'channel_layout' to value '3'
  
  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] Setting 'channels' to value '2'
  
  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] tb:1/48000 samplefmt:s16 samplerate:48000 chlayout:3
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] Setting 'time_base' to value '1/44100'
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] Setting 'sample_rate' to value '44100'
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] Setting 'sample_fmt' to value '1'
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] Setting 'channel_layout' to value '3'
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] Setting 'channels' to value '2'
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] tb:1/44100 samplefmt:s16 samplerate:44100 chlayout:3
  
  FFMPEG: [Parsed_volume_3 @ 0ddfe580] Setting 'volume' to value '2'
  
  FFMPEG: [Parsed_aresample_4 @ 0ddfe660] Setting 'sample_rate' to value '48000'
  
  FFMPEG: [Parsed_aformat_5 @ 0ddfe940] Setting 'sample_fmts' to value 'fltp'
  
  FFMPEG: [Parsed_aformat_5 @ 0ddfe940] Setting 'channel_layouts' to value '3'

  Then, I am trying to add a frame (that has been decoded beforehand) like this :

  // "buffer_source_context" is one of the "inputs[i].buffer_source_context" from the code above
  
  int result = av_buffersrc_write_frame(  buffer_source_context,
  
                                              input_frame);
  
  if (result < 0) {
  
      char errorBuf[1024];
  
      av_make_error_string(errorBuf, 1024, result);
  
      log("Error: While adding to buffer source: %s", errorBuf);
  
      return AVERROR_EXIT;
  
  }

  And the result is the mentioned "invalid argument".

  The buffer_source_context is one of those noted from the code above and the input_frame is perfectly fine as well.
  Before the filtering code was added, the same frame was passed to an encoder instead without a problem.

  I am at a loss at what the error could be here. I log FFmpeg errors at the lowest possible level, but not a single error is shown. I am using FFmpeg 3.1.1.