Read Only .JSON option in ld-analyse & fix graphing issues

[harrypm]

It would be useful to only read the .json from decodes that have had the initial TBC files purged to save space allowing the decoded data to be preserved in a human-viewable format alongside exported video/RF files.

Ideally, this would be exported to a set of SVG & PNG (300% Scale) files today, individually or via an export/export all button in the GUI and via headerless commands and later an autogenerated PDF report would be ideal.

Signal Metadata Handling

• PDF Report Export
• SVG Export of Ossiliscope/Vectorscope/Waveform (at the current frame)
• SVG Export of SNR
• SVG Export of Dropout analysis

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• PNG Export of Ossiliscope/Vectorscope/Waveform (at the current frame)
• PNG Export of SNR
• PNG Export of Dropout analysis

CLI Command Additions

• --graphic_export_all - Exports all information in SVG or PNG
• --summary_report - Exports all data in autogenerated PDF
• --graphic_export snr Black & White signal to noise ratio
• --graphic_export dropout Dropout & Visible Dropout

Limit SNR Readout

• Limit SNR Based on tape format

On formats like VHS etc sometimes SNR values can spike high making a graph that's laughably unreadable on less than 4k displays due to the GUI scaling requiring to screenshot it and zoom into the bottom.

I don't think any tape/recorded format will go past 65-70db of SNR in the real world but this should really be limited on a format flag basis as I do not know the exact potential numbers for full spec live composite that's been decoded or encoded.

[happycube]

Yeah that's a bit nuts. Should add a hard-cap to ld/vhs-decode. Anything >60dB is probably wrong, I think a perfect LD disk with overly-active deemphasis (i.e. trading sharpness for SNR) gets about 50-52dB.