Cryptic `ffmpeg` + Python error: `Cannot find a matching stream for unlabeled input pad 0 on filter Parsed_crop_1`

Question

I want to use ffmpeg with Python in a Jupyter notebook to create a video from 2000 PNG image files generated by matplotlib . I'm on a Windows 7 machine.

The frames are very narrow and high, so I'd like to cut them vertically into seven equal-sized "tiles" using crop and stacked those "tiles" horizontally using hstack , but I'm getting only getting cryptic error messages:

ffmpeg_path = notebook_directory    # Make sure ffmpeg.exe is in notebook directory!

frames_path = 'C:\\Users\\Username\\Desktop'
frames_renamed_path = os.path.join(frames_path, 'renamed')
os.chdir(frames_renamed_path)    # Temporarily change current working directory

check_call(
    [
        os.path.join(ffmpeg_path, 'ffmpeg'),
        '-y',    # Overwrite output files without asking
        '-report',    # Write logfile to current working directory
        '-hwaccel', 'cuda',    # Use GPU acceleration
        '-framerate', '60',    # Input frame rate
        '-i', os.path.join(frames_renamed_path, 'frame%05d.png'),    # Path to input frames
        #'-r', '60',    # Output frame rate
        #'-vf', 'pad=ceil(iw/2)*2:ceil(ih/2)*2',    # Pad frames to even pixel numbers (required by many codecs)
        #'-pix_fmt', 'yuv420p',
        '-pix_fmt', 'rgb32',    # Use RGB32 pixel format matching MatPlotLib image output
        '-filter_complex',    # Cut frames into tiles and rearrange (here: 7 horizontal tiles)
            'crop=in_w:in_h/7:0:0[tile_1],'    # 1st tile from top
            + 'crop=in_w:in_h/7:0:in_h*1/7[tile_2],'    # 2nd tile from top
            + 'crop=in_w:in_h/7:0:in_h*2/7[tile_3],'    # 3rd tile from top
            + 'crop=in_w:in_h/7:0:in_h*3/7[tile_4],'    # 4th tile from top
            + 'crop=in_w:in_h/7:0:in_h*4/7[tile_5],'    # 5th tile from top
            + 'crop=in_w:in_h/7:0:in_h*5/7[tile_6],'    # 6th tile from top
            + 'crop=in_w:in_h/7:0:in_h*6/7[tile_7],'    # 7th tile from top
            + '[tile_1][tile_2][tile_3][tile_4][tile_5][tile_6][tile_7]hstack=7',    # Stack tiles horizontally
        os.path.join(frames_renamed_path, 'video.mp4')    # Path to store output video
    ]
)

os.chdir(notebook_directory)    # Reset current working directory to notebook directory

---------------------------------------------------------------------------
CalledProcessError                        Traceback (most recent call last)
Input In [10], in <cell line: 9>()
      6 frames_renamed_path = os.path.join(frames_path, 'renamed')
      7 os.chdir(frames_renamed_path)    # Temporarily change current working directory
----> 9 check_call(
     10     [
     11         os.path.join(ffmpeg_path, 'ffmpeg'),
     12         '-y',    # Overwrite output files without asking
     13         '-report',    # Write logfile to current working directory
     14         '-hwaccel', 'cuda',    # Use GPU acceleration
     15         '-framerate', '60',    # Input frame rate
     16         '-i', os.path.join(frames_renamed_path, 'frame%05d.png'),    # Path to input frames
     17         #'-pattern_type', 'glob', '-i', os.path.join(frames_renamed_path, '*.png'),    # glob not available in Windows by default
     18         #'-r', '60',    # Output frame rate
     19         '-vf', 'pad=ceil(iw/2)*2:ceil(ih/2)*2',    # Pad frames to even pixel numbers (required by many codecs)
     20         #'-pix_fmt', 'yuv420p',
     21         '-pix_fmt', 'rgb32',    # Use RGB32 pixel format matching MatPlotLib image output
     22         '-filter_complex',    # Cut frames into tiles and rearrange (here: 7 horizontal tiles)
     23             'crop=in_w:in_h/7:0:0[tile_1],'    # 1st tile from top
     24             + 'crop=in_w:in_h/7:0:in_h*1/7[tile_2],'    # 2nd tile from top
     25             + 'crop=in_w:in_h/7:0:in_h*2/7[tile_3],'    # 3rd tile from top
     26             + 'crop=in_w:in_h/7:0:in_h*3/7[tile_4],'    # 4th tile from top
     27             + 'crop=in_w:in_h/7:0:in_h*4/7[tile_5],'    # 5th tile from top
     28             + 'crop=in_w:in_h/7:0:in_h*5/7[tile_6],'    # 6th tile from top
     29             + 'crop=in_w:in_h/7:0:in_h*6/7[tile_7],'    # 7th tile from top
     30             + '[tile_1][tile_2][tile_3][tile_4][tile_5][tile_6][tile_7]hstack=7',    # Stack tiles horizontally
     31         os.path.join(frames_renamed_path, 'video.mp4')    # Path to store output video
     32     ]
     33 )
     35 os.chdir(notebook_directory)

File C:\Program Files\Python38\lib\subprocess.py:364, in check_call(*popenargs, **kwargs)
    362     if cmd is None:
    363         cmd = popenargs[0]
--> 364     raise CalledProcessError(retcode, cmd)
    365 return 0

CalledProcessError: Command '['C:\\Users\\Username\\Desktop\\ffmpeg\\ffmpeg', '-y', '-report', '-hwaccel', 'cuda', '-framerate', '60', '-i', 'C:\\Users\\Username\\Desktop\\renamed\\frame%05d.png', '-vf', 'pad=ceil(iw/2)*2:ceil(ih/2)*2', '-pix_fmt', 'rgb32', '-filter_complex', 'crop=in_w:in_h/7:0:0[tile_1],crop=in_w:in_h/7:0:in_h*1/7[tile_2],crop=in_w:in_h/7:0:in_h*2/7[tile_3],crop=in_w:in_h/7:0:in_h*3/7[tile_4],crop=in_w:in_h/7:0:in_h*4/7[tile_5],crop=in_w:in_h/7:0:in_h*5/7[tile_6],crop=in_w:in_h/7:0:in_h*6/7[tile_7],[tile_1][tile_2][tile_3][tile_4][tile_5][tile_6][tile_7]hstack=7', 'C:\\Users\\Username\\Desktop\\renamed\\video.mp4']' returned non-zero exit status 1.

This is the ffmpeg log output (cropped):

ffmpeg started on 2022-08-04 at 01:17:19
Report written to "ffmpeg-20220804-011719.log"
Log level: 48
Command line:
"C:\\Users\\Username\\Desktop\\ffmpeg\\ffmpeg" -y -report -hwaccel cuda -framerate 60 -i "C:\\Users\\Username\\Desktop\\renamed\\frame%05d.png" -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2" -pix_fmt rgb32 -filter_complex "crop=in_w:in_h/7:0:0[tile_1],crop=in_w:in_h/7:0:in_h*1/7[tile_2],crop=in_w:in_h/7:0:in_h*2/7[tile_3],crop=in_w:in_h/7:0:in_h*3/7[tile_4],crop=in_w:in_h/7:0:in_h*4/7[tile_5],crop=in_w:in_h/7:0:in_h*5/7[tile_6],crop=in_w:in_h/7:0:in_h*6/7[tile_7],[tile_1][tile_2][tile_3][tile_4][tile_5][tile_6][tile_7]hstack=7" "C:\\Users\\Username\\Desktop\\renamed\\video.mp4"
ffmpeg version 2022-07-14-git-882aac99d2-full_build-www.gyan.dev Copyright (c) 2000-2022 the FFmpeg developers
  built with gcc 12.1.0 (Rev2, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libdav1d --enable-libdavs2 --enable-libuavs3d --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxvid --enable-libaom --enable-libjxl --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-libshaderc --enable-vulkan --enable-libplacebo --ena  libavutil      57. 29.100 / 57. 29.100
  libavcodec     59. 38.100 / 59. 38.100
  libavformat    59. 28.100 / 59. 28.100
  libavdevice    59.  8.100 / 59.  8.100
  libavfilter     8. 45.100 /  8. 45.100
  libswscale      6.  8.100 /  6.  8.100
  libswresample   4.  8.100 /  4.  8.100
  libpostproc    56.  7.100 / 56.  7.100
Splitting the commandline.
Reading option '-y' ... matched as option 'y' (overwrite output files) with argument '1'.
Reading option '-report' ... matched as option 'report' (generate a report) with argument '1'.
Reading option '-hwaccel' ... matched as option 'hwaccel' (use HW accelerated decoding) with argument 'cuda'.
Reading option '-framerate' ... matched as AVOption 'framerate' with argument '60'.
Reading option '-i' ... matched as input url with argument 'C:\Users\Username\Desktop\renamed\frame%05d.png'.
Reading option '-vf' ... matched as option 'vf' (set video filters) with argument 'pad=ceil(iw/2)*2:ceil(ih/2)*2'.
Reading option '-pix_fmt' ... matched as option 'pix_fmt' (set pixel format) with argument 'rgb32'.
Reading option '-filter_complex' ... matched as option 'filter_complex' (create a complex filtergraph) with argument 'crop=in_w:in_h/7:0:0[tile_1],crop=in_w:in_h/7:0:in_h*1/7[tile_2],crop=in_w:in_h/7:0:in_h*2/7[tile_3],crop=in_w:in_h/7:0:in_h*3/7[tile_4],crop=in_w:in_h/7:0:in_h*4/7[tile_5],crop=in_w:in_h/7:0:in_h*5/7[tile_6],crop=in_w:in_h/7:0:in_h*6/7[tile_7],[tile_1][tile_2][tile_3][tile_4][tile_5][tile_6][tile_7]hstack=7'.
Reading option 'C:\Users\Username\Desktop\renamed\video.mp4' ... matched as output url.
Finished splitting the commandline.
Parsing a group of options: global .
Applying option y (overwrite output files) with argument 1.
Applying option report (generate a report) with argument 1.
Applying option filter_complex (create a complex filtergraph) with argument crop=in_w:in_h/7:0:0[tile_1],crop=in_w:in_h/7:0:in_h*1/7[tile_2],crop=in_w:in_h/7:0:in_h*2/7[tile_3],crop=in_w:in_h/7:0:in_h*3/7[tile_4],crop=in_w:in_h/7:0:in_h*4/7[tile_5],crop=in_w:in_h/7:0:in_h*5/7[tile_6],crop=in_w:in_h/7:0:in_h*6/7[tile_7],[tile_1][tile_2][tile_3][tile_4][tile_5][tile_6][tile_7]hstack=7.
Successfully parsed a group of options.
Parsing a group of options: input url C:\Users\Username\Desktop\renamed\frame%05d.png.
Applying option hwaccel (use HW accelerated decoding) with argument cuda.
Successfully parsed a group of options.
Opening an input file: C:\Users\Username\Desktop\renamed\frame%05d.png.
[image2 @ 00000000005db0c0] Opening 'C:\Users\Username\Desktop\renamed\frame00000.png' for reading
[file @ 00000000005f6c00] Setting default whitelist 'file,crypto,data'
[AVIOContext @ 00000000005fed40] Statistics: 28860 bytes read, 0 seeks

<...>

[AVIOContext @ 00000000005fda00] Statistics: 67659 bytes read, 0 seeks
[image2 @ 00000000005db0c0] Probe buffer size limit of 5000000 bytes reached
Input #0, image2, from 'C:\Users\Username\Desktop\renamed\frame%05d.png':
  Duration: 00:00:25.00, start: 0.000000, bitrate: N/A
  Stream #0:0, 80, 1/60: Video: png, rgba(pc), 1200x1857 [SAR 3937:3937 DAR 400:619], 60 fps, 60 tbr, 60 tbn
Successfully opened the file.
[Parsed_crop_0 @ 00000000005fdc40] Setting 'out_w' to value 'in_w'
[Parsed_crop_0 @ 00000000005fdc40] Setting 'out_h' to value 'in_h/7'
[Parsed_crop_0 @ 00000000005fdc40] Setting 'x' to value '0'
[Parsed_crop_0 @ 00000000005fdc40] Setting 'y' to value '0'
[Parsed_crop_1 @ 0000000000607500] Setting 'out_w' to value 'in_w'
[Parsed_crop_1 @ 0000000000607500] Setting 'out_h' to value 'in_h/7'
[Parsed_crop_1 @ 0000000000607500] Setting 'x' to value '0'
[Parsed_crop_1 @ 0000000000607500] Setting 'y' to value 'in_h*1/7'
[Parsed_crop_2 @ 0000000000607880] Setting 'out_w' to value 'in_w'
[Parsed_crop_2 @ 0000000000607880] Setting 'out_h' to value 'in_h/7'
[Parsed_crop_2 @ 0000000000607880] Setting 'x' to value '0'
[Parsed_crop_2 @ 0000000000607880] Setting 'y' to value 'in_h*2/7'
[Parsed_crop_3 @ 0000000000607c00] Setting 'out_w' to value 'in_w'
[Parsed_crop_3 @ 0000000000607c00] Setting 'out_h' to value 'in_h/7'
[Parsed_crop_3 @ 0000000000607c00] Setting 'x' to value '0'
[Parsed_crop_3 @ 0000000000607c00] Setting 'y' to value 'in_h*3/7'
[Parsed_crop_4 @ 00000000005fda00] Setting 'out_w' to value 'in_w'
[Parsed_crop_4 @ 00000000005fda00] Setting 'out_h' to value 'in_h/7'
[Parsed_crop_4 @ 00000000005fda00] Setting 'x' to value '0'
[Parsed_crop_4 @ 00000000005fda00] Setting 'y' to value 'in_h*4/7'
[Parsed_crop_5 @ 0000000002b8f800] Setting 'out_w' to value 'in_w'
[Parsed_crop_5 @ 0000000002b8f800] Setting 'out_h' to value 'in_h/7'
[Parsed_crop_5 @ 0000000002b8f800] Setting 'x' to value '0'
[Parsed_crop_5 @ 0000000002b8f800] Setting 'y' to value 'in_h*5/7'
[Parsed_crop_6 @ 0000000000607d00] Setting 'out_w' to value 'in_w'
[Parsed_crop_6 @ 0000000000607d00] Setting 'out_h' to value 'in_h/7'
[Parsed_crop_6 @ 0000000000607d00] Setting 'x' to value '0'
[Parsed_crop_6 @ 0000000000607d00] Setting 'y' to value 'in_h*6/7'
[Parsed_hstack_7 @ 0000000002b8fb80] Setting 'inputs' to value '7'
Cannot find a matching stream for unlabeled input pad 0 on filter Parsed_crop_1

What is the problem here? Also, how does one interpret this cryptic error message at the end of the log output:

Cannot find a matching stream for unlabeled input pad 0 on filter Parsed_crop_1

Eg what is input pad 0 , why is it unlabeled , and why can't it find a matching stream?

(PS.: Yes, I do have a habit of excessively documenting my code. ^^)

Answer 1

The error is a result of incorrect usage of filter_complex .

• The separator between the output name (eg [tile_1] ) and the next filter should be ; instead of , .
  (The comma syntax is used for chaining filters that comes directly one after the other).
• The input for each filter like crop=in_w:in_h/7:0:0[tile_1] should be defined.
  Add [0] at the beginning of each part, for defining the "first input stream" as the input to the filter.
  Replace crop=in_w:in_h/7:0:0[tile_1] with [0]crop=in_w:in_h/7:0:0[tile_1] and crop=in_w:in_h/7:0:in_h*1/7[tile_2] with [0]crop=in_w:in_h/7:0:in_h*1/7[tile_2] ...

---

Corrected code (with my paths):

from subprocess import check_call
import os

ffmpeg_path = 'C:\\FFmpeg\\bin' # Make sure ffmpeg.exe is in the directory!

frames_path = 'C:\\Users\\Rotem\\Desktop'
frames_renamed_path = os.path.join(frames_path, 'renamed')
os.chdir(frames_renamed_path)    # Temporarily change current working directory


check_call(
    [
        os.path.join(ffmpeg_path, 'ffmpeg'),
        '-y',    # Overwrite output files without asking
        '-report',    # Write logfile to current working directory
        '-hwaccel', 'cuda',    # Use GPU acceleration
        '-framerate', '60',    # Input frame rate
        '-i', os.path.join(frames_renamed_path, 'frame%05d.png'),    # Path to input frames
        '-pix_fmt', 'rgb32',    # Use RGB32 pixel format matching MatPlotLib image output
        '-filter_complex',    # Cut frames into tiles and rearrange (here: 7 horizontal tiles)
            '[0]crop=in_w:in_h/7:0:0[tile_1];'    # 1st tile from top
            + '[0]crop=in_w:in_h/7:0:in_h*1/7[tile_2];'    # 2nd tile from top
            + '[0]crop=in_w:in_h/7:0:in_h*2/7[tile_3];'    # 3rd tile from top
            + '[0]crop=in_w:in_h/7:0:in_h*3/7[tile_4];'    # 4th tile from top
            + '[0]crop=in_w:in_h/7:0:in_h*4/7[tile_5];'    # 5th tile from top
            + '[0]crop=in_w:in_h/7:0:in_h*5/7[tile_6];'    # 6th tile from top
            + '[0]crop=in_w:in_h/7:0:in_h*6/7[tile_7];'    # 7th tile from top
            + '[tile_1][tile_2][tile_3][tile_4][tile_5][tile_6][tile_7]hstack=7',    # Stack tiles horizontally
        os.path.join(frames_renamed_path, 'video.mp4')    # Path to store output video
    ]
)

---

Notes:

• -hwaccel cuda has no affect here, because the input format is PNG (and CUDA acceleration is not supported).
• -pix_fmt rgb32 has no affect, since the default video codec is libx264 , and it changes the format to yuv444p ( rgb32 is not supported).
• As flaxon commented, "first get the ffmpeg command to work in console" (next time).