Use ffmpeg to record 2 webcams on raspberry pi - ffmpeg

Question

I want to record 2 webcams using ffmpeg, i have a simple python script but it doesn't work when I run the 2 subprocesses at the same time.
ROOT_PATH = os.getenv("ROOT_PATH", "/home/pi")
ENCODING = os.getenv("ENCODING", "copy")
new_dir = datetime.datetime.now().strftime("%Y_%m_%d_%H_%M_%S")
RECORDINGS_PATH1 = os.getenv("RECORDINGS_PATH", "RecordingsCam1")
RECORDINGS_PATH2 = os.getenv("RECORDINGS_PATH", "RecordingsCam2")
recording_path1 = os.path.join(ROOT_PATH, RECORDINGS_PATH1, new_dir)
recording_path2 = os.path.join(ROOT_PATH, RECORDINGS_PATH2, new_dir)
os.mkdir(recording_path1)
os.mkdir(recording_path2)
segments_path1 = os.path.join(recording_path1, "%03d.avi")
segments_path2 = os.path.join(recording_path2, "%03d.avi")
record1 = "ffmpeg -nostdin -i /dev/video0 -c:v {} -an -sn -dn -segment_time 30 -f segment {}".format(ENCODING, segments_path1)
record2 = "ffmpeg -nostdin -i /dev/video2 -c:v {} -an -sn -dn -segment_time 30 -f segment {}".format(ENCODING, segments_path2)
subprocess.Popen(record1, shell=True)
subprocess.Popen(record2, shell=True)
Also, i tried capturing the 2 sources side by side but it gives the error:`Filtering and streamcopy cannot be used together.

Answer 1

This has nothing to do with running two processes at the same time. FFmpeg clearly states that it cannot find /dev/video0 and /dev/video2. It seems your video camera is not detected. You can check this with following command :
$ ls /dev/ | grep video
will list all devices which have video in their name. If video0 and video2 do not exist, its clear FFmpeg gives such error. If they do exist, i do not know how to resolve this. You may try to run the FFmpeg commands directly in terminal.