Save an RTSP stream as a ISO BMFF-compliant MPEG-4 file

save_rtsp.py

#!/usr/bin/env python
import argparse
import os
import subprocess
import struct

parser = argparse.ArgumentParser()
parser.add_argument('--output', '-o', type=argparse.FileType('wb'))
parser.add_argument('rtsp_stream')
args = parser.parse_args()


proc = subprocess.Popen(
    args=[
        'ffmpeg',
        '-hide_banner', '-loglevel', 'warning', '-nostats',

        '-rtsp_transport', 'tcp',  # https://stackoverflow.com/a/61042765
        '-i', args.rtsp_stream,

        '-c:v', 'copy',  # copy video stream
        '-an',  # discard audio stream

        # https://developer.mozilla.org/en-US/docs/Web/API/Media_Source_Extensions_API/Transcoding_assets_for_MSE
        '-f', 'mp4',
        '-movflags', 'frag_keyframe+empty_moov',

        '-',  # output to stdout
    ],
    stdout=subprocess.PIPE
)


while True:
    try:
        box_header = proc.stdout.read(8)
        if len(box_header) == 0:
            break
        
        size, type = struct.unpack('>L4s', box_header)
        if size == 1:
            size, = struct.unpack('>Q', proc.stdout.read(8))
        
        if size == 0:
            box = box_header + proc.stdout.read()
        else:
            box = box_header + proc.stdout.read(size - 8)

        print(f'Read box of type {type!r} and length {size}')
        if args.output:
            args.output.write(box)
    except KeyboardInterrupt:
        proc.terminate()
        break