Psvbi

From M1Research

Revision as of 17:13, 7 January 2006

psvbi - Pseudo VBI

Overview

psvbi software complex was developed for trasmitting control commands in TV video signal. Data block coded into some lines of video signal and could be used as marks for remote stations or analytic system. It much easy to implement and control (and diag) instead of real VBI due to high cost of equipment.

How does it works

Base Theory

Data to transmit coded by 14 bytes block. Each block transmitted in one video frame. Data encoded as luminance part of video signal (most stable to MPEG encoding/decoding) in some video lines (in our case we prefer to use top 2..4 lines - not visible on home equipment, only professional monitors with turned on underscan area could be used to SEE if data real present). During coding data used Hamming Error Correction Code and permutations alorithms to make more stable transmitting data, but some times it was noticed false data detection :-(((, use control sum algorithms in analizator to check if it's your real data packed :-))).

Embedding data

Embedding data performed by VirtualDub software (real greate program). Embedding and encoding data performed by our plug-in.

Make sure you have VirtualDub and copied pseudovbi.vdf to VirtualDub's plugin folder.

Start VirtualDub, open desired video file (in our case we use Matrox Digisuite for capturing and playback). Open Video -> Filters and select pseudovbi plugin. As result you can see plugin dialog window:

Encoding/Embeding parametes:

• Start encoding from - define start frame number of video to insert data;
• Frames to encode - number of frames (duration on frames) of encoded data block;
• Data block - hexadiminal presentation of 14 bytes lenght data block;
• Setup/"Luma" level - defines value is used to encode data (0...255);
• Inserting Position - this blocks define where data will be inserted (position on screen). We prefer use top 2 rows (video lines) to insert;
  • BLOCK - enable/disable insert block;
  • COLUMN - start position (from left) where data begin to inserts
  • ROW - row/line number where data begin to inserts;

Result of plugin: (fragment of VirtualDub program interface)

As result you can see a dot sequence in first 2 lines of frame. Now data block embedded. You can print this video to tape or video server.

Demembedding of data

Dembedding of data performed by another part of software.

This software capture video using V4L2 base interface (we use bttv878 based capture card) perform alization and in a case of detection datablock it call plugins method that perform higher level data decoding (application level).

Application startup parameters:

[root@dev-2 decoder]# ./psvbid --help
Usage: psvbid <args>
args:
        --demonize=N    0-no daemon mode, 1-demonize (default 0)
        --white-level=N White level of signal (default 96)
        --pos-x-start=N left 'x' position of search block (default 10)
        --pos-x-stop=N  right 'x' position of search block (default 30)
        --pos-y-start=N top 'y' position of search block (default 0)
        --pos-y-stop=N  bottom 'y' position of search block (default 10)
        --video-dev=S   video device to grab video from (default '/dev/video0')
        --load-plugin=S load handler plugin (multiple allowed, max 10)
        --verbose-video-init    show more info during init v4l2 device (default 0)
        --help  Show program usage

Real application startup:

[root@dev-2 decoder]# ./psvbid --load-plugin=m1cmds --verbose-video-init --pos-y-stop=5

API interface for own analizator

Software

Real example