merge_slate_with_video.py

def merge_slate_with_video(slate_path, video_path):
    # Process w/ FFMPEG
    with open("output.log", "a") as output:

        # Generate intermediate transport streams to prevent re-encoding of h.264
        print("Generating intermediate1.ts")
        subprocess.call(
            """docker run -v $(pwd):$(pwd) -w $(pwd) jrottenberg/ffmpeg:3.2-scratch -y -i '{}' -c copy -bsf:v h264_mp4toannexb -f mpegts ./temp/intermediate1.ts""".format(slate_path),
            shell=True, stdout=output, stderr=output
        )
        print("Done Generating intermediate1.ts")
        print("Creating intermediate2.ts")
        subprocess.call(
            """docker run -v $(pwd):$(pwd) -w $(pwd) jrottenberg/ffmpeg:3.2-scratch -y -i ./temp/temp_black.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts ./temp/intermediate2.ts""",
            shell=True, stdout=output, stderr=output
        )
        print("Done Generating intermediate2.ts")
        print("Creating intermediate3.ts")
        subprocess.call(
            """docker run -v $(pwd):$(pwd) -w $(pwd) jrottenberg/ffmpeg:3.2-scratch -y -i '{}' -c copy -bsf:v h264_mp4toannexb -f mpegts ./temp/intermediate3.ts""".format(video_path),
            shell=True, stdout=output, stderr=output
        )
        print("Done Generating intermediate3.ts")
        print("Beginning merge...")

        # Merge together transport streams
        subprocess.call(
            """docker run -v $(pwd):$(pwd) -w $(pwd) jrottenberg/ffmpeg:3.2-scratch -y -i 'concat:./temp/intermediate1.ts|./temp/intermediate2.ts|./temp/intermediate3.ts'  -c copy -bsf:a aac_adtstoasc ./temp/slated_output.mp4""",
            shell=True, stdout=output, stderr=output
        )
        print("Merge completed... Ready to upload!")

    return "temp/slated_output.mp4"