import os
import subprocess

import av
import av.datasets


# We want an H.264 stream in the Annex B byte-stream format.
# We haven't exposed bitstream filters yet, so we're gonna use the `ffmpeg` CLI.
h264_path = 'night-sky.h264'
if not os.path.exists(h264_path):
    subprocess.check_call([
        'ffmpeg',
        '-i', av.datasets.curated('pexels/time-lapse-video-of-night-sky-857195.mp4'),
        '-vcodec', 'copy',
        '-an',
        '-bsf:v', 'h264_mp4toannexb',
        h264_path,
    ])


fh = open(h264_path, 'rb')

codec = av.CodecContext.create('h264', 'r')

while True:

    chunk = fh.read(1 << 16)

    packets = codec.parse(chunk)
    print("Parsed {} packets from {} bytes:".format(len(packets), len(chunk)))

    for packet in packets:

        print('   ', packet)

        frames = codec.decode(packet)
        for frame in frames:
            print('       ', frame)

    # We wait until the end to bail so that the last empty `buf` flushes
    # the parser.
    if not chunk:
        break