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

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.

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.