RF Capture Decoding Guide

Welcome to the 21st, its the future.

Software decoding simply is just doing what was done on dedicated compoents, then on dedicated IC's and finally on FPGAs, its not magic and its not a blackbox hardware either its entirely software emulating the abbilitys of hardware with an order of magnitude more flexiblity.

Do you need to know about programming?

No.

Do you need to know how to use basic systems on a computer.

Yes.

Do you need to have a basic understanding of a VCR does and what a TBC does?

Yes.

It makes life easyer and decoding a thoughtless copy-paste clean, new tape, clean, hit enter and decode workflow after hardware hookup.

Resorce Usage

Chroma-Decoder can use around 20GB~33GB of ram with FFmpeg it will work with less.

decoders however are cpu bound and will use normally less then 500MB of ram

Running the decoders

There are 4 decoders are bundled inside vhs-decode respiatory and windows version

cd vhs-decode - Enter the directory

Inside a terminal use

vhs-decode / ld-decode / cvbs-decode / hifi-decode

For windows:

decode.exe vhs / decode.exe ld / decode.exe cvbs / decode.exe hifi

Followed by arguments you can read the Full Command List for there use and effects.

You need to always set a few mandatory things

TV System, Input Sample Rate (unless DdD captures), Input file & Outfile Name

Example: vhs-decode --debug --tape_format vhs --system pal --cxadc --threads 8 --recheck_phase my-tape.u8 my-tape-decoded

Example: vhs-decode --debug -p -t 8 --tf vhs --cxadc --recheck_phase

Ctrl+C Will kill the current process, use this to stop the capture manually.

Press Ctrl+C to copy then Ctrl+P to past the command use <+> to move edit position on the command line to edit the name or command and Enter to run the command.

Determnaing Quaility

Black SNR Signal To Noise Ratio

Sudden dips in the graph are ware there are dropouts, interfrrance or weak signal.

60~70 dB - Live Composite

40~50 dB - Great Signal

30~40 dB - Good Signal

20~30 dB - Weak Signal

10~20 dB - Poor Signal

CVBS-Decode

CVBS-Decode, decodes raw composite signals.

You capture the normal composite video signal out of a device, in raw RF values then save it to file, you have full control over the baseband processing, fine control over how colour is processed and you have a full 625/525 lines of image information.

HiFi-Decode

There is the full hifi-decode and the universal RTLSDR HiFi-Decode which is a GNU radio script.

FM Audio decoding has been normal for decades if you ever have used a car you know it has a radio and it picks up and decodes FM audio signals from local stations.

HiFi decode allows you to have full control over the de-modulation and noise filtering process this can remove and improve on sound quality drastically in some cases and or save you money if you dont have the best amplifyers or a decent audio interface capture solution, if you have good hearing you will notice the diffrance quickly with even 15USD Bheringer ''studio'' headpones.

You can use an cheep RTLSDR or the DdD & CX Cards for capture.

ld-decode (LaserDisc Decoding)

It all started with Laserdisc, the TBC format, software time base correction eveything is built of the inital drive to decode the BBC 1986 Domes Day Discs.

This decoder is bundled inside the vhs-decode repository

VHS-Decode

Finally the reason you most likely came here in the first palce, slavation from hardware limited processing, well thats what it is

Basic Decoding Command Examples

CVBS-Decode

./cvbs-decode --debug --threads 8 -p -A --cxadc CX_Blue_Level_0db_6db_off_CXADC.u8 CX_Blue_Level_0db_6db_off_CXADC

VHS-Decode

./vhs-decode --debug --threads 8 -p --ct --recheck_phase

HiFi-Decode

./HiFi-decode -p -t 8 Input Tape-name_HiFi_Decode_192khz.flac

HiFi-Decode is a single command system for RF to Playable files.

Processing Vertical Blanking Interval Data

ld-process-vbi input.tbc / ld-prcoess-vits input.tbc Will decode most Vertical Blanking Interval Data.

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