CVBS Composite Decode

CVBS Decode

This spin-off project uses RAW CVBS captures and uses the signal processing and time base correction code, from vhs-decode & ld-decode there is no de-modulation stage unlike FM based media.

Introduction

Full 4fsc CVBS PAL frame with SMPTE color bars. - 3D Transform Decoder.

Internet Archive / Google Drive Mirror

CVBS an abbreviation,

Composite Video Baseband Signal. (also lesser used: colour, video, blanking, and sync)

Baseband a non-modulated live signal directly off a camera or media generation device, for tape formats this means a de-modulated & processed signal off a recorded medium.

Baseband signals are ready for direct use for audio this means a speaker and for video used to be an analogue CRT TV set now it's all on analogue to digital converter ICs.

Composite analogue video signals have been used from the pre-digital era to early digital equipment, developed in the 1950s and in full use from the 1960s to even today analogue systems using the ''Yellow RCA jack'' on consumer equipment and a BNC jack on prosumer/broadcast equipment.

S-Video is just composite Luminance with the Chromance modulated this minimises colour interference during transport, thus is due to signals being inside a cable with a pair of 2 shield cables shielded S-Video cable or 2 separate BNC cables and then the chroma is demodulated at the input device level, there are 3 versions of this standard.

CVBS Resolution Standards

Signal Format	Resolution	Field System	TV System	Aspect Ratio	RF Capture Support	Video Decoding Support
CVBS	525 Lines	Interlaced	525 NTSC	4:3 / 16:9	Yes*	Yes*
CVBS	625 Lines	Interlaced	625 PAL	4:3 / 16:9	Yes*	Yes*
CVBS	655 Lines	Interlaced	PAL	4:3	Yes*	Not Tested/Implemented
CVBS	405 Lines	Interlaced	PAL	4:3	Yes*	Not Tested/Implemented
CVBS	819 Lines	Interlaced	PAL	4:3	Yes*	Not Tested/Implemented
CVBS 240p	240 Lines	Progressive	NTSC	4:3 / 16:9	Yes*	Work in Progress
CVBS 288p	288 Lines	Progressive	PAL	4:3 / 16:9	Yes*	Work in Progress
960h CCTV	960 x 576	Interlaced	N/A	16:9 Only	Yes*	Not Tested

Capturing RAW CVBS

Important

28msps+ is recommended for sampling CVBS signals directly.

MISRC Has support for native RAW Composite/CVBS and S-Video capture in 12-bit (16-bit 40msps singed or unsigned samples).

CX Cards can try to switch back into standard mode causing wavy, jiggling, and loss of vertical sync frames, however if the card is in a fixed low gain state (level 0 / sixdb off) it is possible to get clean stable captures.

There is also using a T adaptor to feed a secondary signal via waveform generator to keep CX Cards in raw output mode, then in post to low pass filter it and then decode it.

The DomesDay Duplicator (DdD) input filtering is not suited for said signal range, the input filtering stage needs to be modified currently, this does not work well as it captures the signal improperly.

There is many more options possible thanks to Hasdoa workflow enabling a wide range of new ADC platforms to be built such as the MISRC.

Installation

cvbs-decode is included inside the vhs-decode install, and is ready to go on self-contained builds.

However for Linux you might need to do:

python3 setup.py build_ext --inplace

That's it you are ready to use CVBS-Decode!

Usage

Currently, this decoder will work just fine with stable signals and live media.

Warning

Sample/frequency rate of input File & TV System is required for the decoder to work.

Note

-A is mandatory for CVBS-Decode to work currently.

Example Usage Command:

cvbs-decode --frequency 28 --pal -A composite-test_28msps_8-bit.u8 composite-test

To stop the decode press Ctrl+C

Command List

Click the here for the full list for all decoders, the below are just usage commands only for CVBS-Decode.

Set Input Frequency

Just like vhs-decode & ld-decode the default is 40msps 8-bit/10-bit/16-bit input.

Captures can be FLAC compressed (.cvbs) or Uncompressed .u8/u16 etc

-f Frequency Adjust in integers of hz, mhz, ghz or 4fsc/5fsc/8fsc/10fsc

--cxadc 28.6 MHz/8-bit (8fsc) Stock Crystal Native 8xFsc 8bit Unsigned Sampling Mode

--cxadc3 35.8 MHz/8-bit (10fsc) Stock Crystal Native 4xFsc 16bit Filtered Vertical Blanking Interval Data (Not Recommended for capture due to up-sampling)

--10cxadc 14.3 MHz/16-bit (4fsc) Stock Crystal 1.25x 8xFsc 8bit Unsigned Sampling Mode

--10cxadc3 17.9 MHz/16-bit (5fsc) Stock Crystal 1.25x 4xFsc 16bit Filtered Vertical Blanking Interval Data

Set TV System

-n NTSC

--NTSCJ NTSC-J

-p PAL

--pm PAL-M

Decode Control

--debug Enables debug detailed logging output.

-A Automatic Sync Detection (Currently Mandatory For CVBS-Decode to work)

-C Clamp signal (black level) and enable automatic gain control.

-S Seek Frame of Capture

--right_hand_hsync Use right-hand horizontal sync detection.

--ct Chroma Trap, cleans up chroma interference on the luma channel.

--sl Defines sharpness by default this is set to 0. (0-100 Range)

--notch Define the centre frequency for the optional built-in notch "bandpass" filter.

--notch_q defines the Q factor Intended primarily for reducing noise from interference however, the decoder logic already compensates based on tape type and TV System values.

File Output

cvbs-decode only outputs 3 files

filename.tbc - 4fsc Luminance & Chrominance Image Data

filename.tbc.json - Frame Descriptor Table (Resolution/Dropouts/SNR/Frames/VBI Data)

filename.log - Timecode Indexed Action/Output Log

Inspect TBC and adjust inside ld-analyse

ld-analyse composite.tbc

Export to Video File

The TBC-Video-Export tool will automatically detect NTSC/PAL input, it can also run ld-dropout correct & ld-process-vbi and will embed the updated .json file inside the mkv, and export a FFV1 10-bit 4:2:2 interlaced file, read the wiki doc for detailed use of its profiles.

Linux, MacOS & Windows:

tbc-video-export composite-test.tbc

Note

You can also manually export via the chroma-decoder directly for any single composite type .tbc media type such as LD/CVBS/SMPTE-C.

Time Base Corrected Output

The Composite signal is stored in a single .tbc

This is a lossless digital file of the entire baseband composite signal like a D2/D3 digital tape.

Full 4fsc 1135x625 PAL (17727262 hz) (25i) (4.2GB/min) (560mbps)

Full 4fsc 910x525 NTSC (14318181 hz) (29.97i) (3.4GB/min) (453mbps)

Issues

• Chroma issues with NTSC VHS use ntsc-phase-comp with chroma-decoder.

• CVBS-Decode is not like ld-decode or vhs-decode so highly unstable sources will most likely require tinkering.

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