Simple RTSP H264 NVR application for Linux using FFmpeg.

Configuration:
    INI and JSON configuration file formats are supported.
    Configuration file path may be passed as the first argument (e. g. nvr /etc/nvr.ini).
    If the configuration file name ends with .json, it's treated as JSON and parsed accordingly.
    By default, config.ini form the current directory is used.
    See the config.example.ini and config.example.json files for reference.
    Sections and directives:
        - nvr
            - storage_dir: directory for storing video segments.
            - segment_length: video file length in milliseconds - inaccurate because streams are split by keyframes;
              set to 0 for a single segment
            - retry_delay: delay between reconnection attempts for a failed stream in milliseconds;
              set to 0 for immediate retry
            - conn_timeout: connection timeout in milliseconds;
              set to 0 to disable connection timeout
            - recv_timeout: packet receive timeout in milliseconds;
              stream will be considered failed and restarted after this timeout;
              set to 0 to disable packet timeout
            - log_file, log_level, log_ffmpeg_level: see the Logging section
        - cameras: "key = value" pairs of camera name and RTSP URI; username:password should be specified inline

Logging:
    Log messages are written to stdout and log_file if specified.
    There are 5 log levels: fatal, error, warning and debug, the minimal level is set with the log_level directive.
    FFmpeg log has its own directive - ffmpeg_log_level and the levels are: panic, fatal, error, warning, info, verbose,
    debug and quiet.
    Log message consists of the following fields:
        - local date and time in ISO 8601 format, including milliseconds and time zone offset
        - [camera name or "main" for the master thread]
        - [log level or "ffmpeg" for FFmpeg messages]
        - the body of the message (in case of FFmpeg message it has two additional fields before the message):
            - [AVClass name or empty string]
            - [FFmpeg log level]

Signals:
    On SIGHUP, the configuration file is being reread and the log file is being reopened.
    On SIGINT (Ctrl + C) and SIGTERM, application is being shut down gracefully and MP4 trailers are being written.
    On the second SIGINT or SIGTERM, application is terminated immediately.