Title: Excuting ffmpeg commands using Python to locate *.png failed
Tags: python,bash,ffmpeg

Question: The following command works well if I run it in the Bash terminal.
ffmpeg -framerate 25 -pattern_type glob -i 'data/*.png' -i data/download_youtube/_-91nXXjrVo_cut.wav -c:v libx264 -pix_fmt yuv420p data/download_youtube/_-91nXXjrVo_out.mp4

However, If i run it using os.system() using Python.
os.system(r"ffmpeg -framerate 25 -pattern_type glob -i '/data/share/VFHQ/data/extracted_cropped_face_results/_-91nXXjrVo/Clip+_-91nXXjrVo+P0+C0+F1537-1825/*.png' -i /data/share/VFHQ/data/download_youtube/_-91nXXjrVo_cut.wav -c:v libx264 -pix_fmt yuv420p /data/share/VFHQ/data/download_youtube/out.mp4")

I get Unknown encoder 'libx264'
If I remove the quotation mark inside the commands
os.system(r"ffmpeg -framerate 25 -pattern_type glob -i /data/share/VFHQ/data/extracted_cropped_face_results/_-91nXXjrVo/Clip+_-91nXXjrVo+P0+C0+F1537-1825/*.png -i /data/share/VFHQ/data/download_youtube/_-91nXXjrVo_cut.wav -c:v libx264 -pix_fmt yuv420p /data/share/VFHQ/data/download_youtube/out.mp4")

I get Option pattern_type not found.
So I tried subprocess.run(command,shell=True) , I get same results as shown above.
Running 'subprocess.run()' without Shell will result in the following"
subprocess.run(['ffmpeg', '-framerate', '25','-pattern_type', 'glob', '-i','/data/share/VFHQ/data/extracted_cropped_face_results/_-91nXXjrVo/Clip+_-91nXXjrVo+P0+C0+F1537-1825/*.png',
                '-i','/data/share/VFHQ/data/download_youtube/_-91nXXjrVo_cut.wav','-c:v','libx264','-pix_fmt','yuv420p','/data/share/VFHQ/data/download_youtube/_-91nXXjrVo_out.mp4'])


[image2 @ 0x56001a8fee00] Could find no file with path '/data/share/VFHQ/data/extracted_cropped_face_results/_-91nXXjrVo/Clip+_-91nXXjrVo+P0+C0+F1537-1825/*.png' and index in the range 0-4
/data/share/VFHQ/data/extracted_cropped_face_results/_-91nXXjrVo/Clip+_-91nXXjrVo+P0+C0+F1537-1825/*.png: No such file or directory


With out the quotation marks on the picture directory:
CompletedProcess(args=['ffmpeg', '-framerate', '25', '-pattern_type', 'glob', '-i', '/data/share/VFHQ/data/extracted_cropped_face_results/_-91nXXjrVo/Clip+_-91nXXjrVo+P0+C0+F1537-1825/*.png', '-i', '/data/share/VFHQ/data/download_youtube/_-91nXXjrVo_cut.wav', '-c:v', 'libx264', '-pix_fmt', 'yuv420p', '/data/share/VFHQ/data/download_youtube/_-91nXXjrVo_out.mp4'], returncode=1)

Unknown encoder 'libx264'
with quotation marks around the picture directory (also the correct way to run in the terminal):
subprocess.run(['ffmpeg', '-framerate', '25','-pattern_type', 'glob', '-i',"'/data/share/VFHQ/data/extracted_cropped_face_results/_-91nXXjrVo/Clip+_-91nXXjrVo+P0+C0+F1537-1825/*.png'",
                '-i','/data/share/VFHQ/data/download_youtube/_-91nXXjrVo_cut.wav','-c:v','libx264','-pix_fmt','yuv420p','/data/share/VFHQ/data/download_youtube/_-91nXXjrVo_out.mp4'])

'/data/share/VFHQ/data/extracted_cropped_face_results/_-91nXXjrVo/Clip+_-91nXXjrVo+P0+C0+F1537-1825/*.png': No such file or directory 

It was later found out that I have 2versions of ffmpeg. One is 4.3 the other is 4.4.2
The thing is running a subprocess with quotation marks (I know it is incorrect as it has been explained) will call v4.4.2. Running it without quotation marks will call the v4.3 ffmpeg.
Also from V4.3 log, it suggests  Reading option '-c:v' ... matched as option 'c' (codec name) with argument 'libx264'. but in the end
[wav @ 0x55eaef48b240] After avformat_find_stream_info() pos: 204878 bytes read:294990 seeks:1 frames:50
Guessed Channel Layout for Input Stream #1.0 : stereo
Input #1, wav, from '/data/share/VFHQ/data/download_youtube/_-91nXXjrVo_cut.wav':
  Metadata:
    encoder         : Lavf58.45.100
  Duration: 00:00:11.44, bitrate: 1536 kb/s
    Stream #1:0, 50, 1/48000: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, stereo, s16, 1536 kb/s
Successfully opened the file.
Parsing a group of options: output url /data/share/VFHQ/data/download_youtube/_-91nXXjrVo_out.mp4.
Applying option c:v (codec name) with argument libx264.
Applying option pix_fmt (set pixel format) with argument yuv420p.
Successfully parsed a group of options.
Opening an output file: /data/share/VFHQ/data/download_youtube/_-91nXXjrVo_out.mp4.
Unknown encoder 'libx264'
[AVIOContext @ 0x55eaef487fc0] Statistics: 294990 bytes read, 1 seeks

Answer: Thanks for everyone's contribution.
To locate the problem, we place -report in the ffmpeg argument for a detailed log. Doing this allows me to find out that there are 2 versions of ffmpeg in my system.
To solve the problem, run whereis ffmpeg to locate the 2 versions of ffmpeg then add the absolute directory of the ffmpeg when running it. For instance  /usr/bin/ffmpeg -i xxxxxx
There is a phenomenon where the version of ffmpeg called in Python is not fixed. In other words, the v3.2 is called if I do not quote the directory in the command (which is also not needed for subprocess or os.system()) and 'v4.4.2` will be called if I place quotation marks. This problem is unknown.