ffmpeg concat filter

fcf.py

import subprocess
import os


chunk_frames = 25
chunk_amount = 3
framerate = 25
duration = chunk_frames / framerate


def validation():
    output = subprocess.check_output(
        [
            "ffprobe", "-v", "error", "-count_frames",
            "-select_streams", "v:0",
            "-show_entries", "stream=nb_read_frames",
            "-of", "default=nokey=1:noprint_wrappers=1",
            "temp.mov"
        ],
        cwd=directory
    )
    frames = int(output)
    expected_frames = chunk_frames * chunk_amount
    msg = f"Frames: {frames}\nExpected frames: {expected_frames}"
    assert frames == expected_frames, msg


# Generate videos.
ffmpeg_args = [
    "ffmpeg", "-y", "-v", "9", "-loglevel", "99",
    "-f", "lavfi",
    "-i", f"testsrc=duration={duration}:size=960x540:rate={framerate}",
    "-f", "lavfi",
    "-i", f"sine=frequency=1000:duration={duration}",
    "-pix_fmt", "yuv420p"
]
directory = os.path.join(os.path.dirname(__file__))

video_files = []
for count in range(0, chunk_amount):
    path = os.path.join(directory, f"temp{count}.mov").replace("\\", "/")
    args = ffmpeg_args + [os.path.basename(path)]
    print(subprocess.list2cmdline(args))
    subprocess.call(args, cwd=directory)
    video_files.append(path)

# Concatenation of video only.
ffmpeg_args = ["ffmpeg", "-y", "-v", "9", "-loglevel", "99"]
for f in video_files:
    ffmpeg_args.extend(["-i", f])

ffmpeg_args.append("-filter_complex")
files_count = len(video_files)
filter = ""
for count in range(0, files_count):
    filter += f"[{count}:0] "

filter += f"concat=n={files_count}:v=1:a=0 [v]"
ffmpeg_args.append(filter)
ffmpeg_args.extend(["-map", "[v]", "temp.mov"])
print(subprocess.list2cmdline(ffmpeg_args))
subprocess.call(ffmpeg_args, cwd=directory)

# Validation.
validation()

# Concatenation of video and audio.
ffmpeg_args = ["ffmpeg", "-y", "-v", "9", "-loglevel", "99"]
for f in video_files:
    ffmpeg_args.extend(["-i", f])

ffmpeg_args.append("-filter_complex")
files_count = len(video_files)
filter = ""
for count in range(0, files_count):
    filter += f"[{count}:0] [{count}:1]"

filter += f"concat=n={files_count}:v=1:a=1 [v] [a]"
ffmpeg_args.append(filter)
ffmpeg_args.extend(["-map", "[v]", "-map", "[a]", "temp.mov"])
print(subprocess.list2cmdline(ffmpeg_args))
subprocess.call(ffmpeg_args, cwd=directory)

# Validation.
validation()