Comment by betamaxthetape | Hacker News Reader

Comment by betamaxthetape | Hacker News Reader

Once the tapes have been digitized, the excellent and open source DV Analyzer tool [1] can be used to inspect the digitized file and produce a report indicating sections where there may be issues with the video and / or audio of the tape.

I digitized a large number of family MiniDV tapes a few years ago, since the quality of the footage on the original tapes is better than the DVD recordings made at the time (due to both the DVD MPEG2 recording scheme and the fact that the camera was connected to the DVD recorder over composite video). But some sections of a few of the tapes had suffered serious deterioration, rendering the resulting footage unwatchable.

Using DV Analyser was a great and quick way to identify the clips with a higher than expected number of errors, so I could try to re-grab those tapes, and (if that failed) go back to the DVD recordings. Much quicker than watching every video through in real-time!

There's also the DV Rescue tool [2] (also open source), which seems to actively assist in fixing detected errors, but I haven't got any experience with that.

[1] https://mediaarea.net/DVAnalyzer

[2] https://mediaarea.net/DVRescue

Something I learned from floppies is that different drives (or decks, in this case) have different read characteristics, so the "bad" segments of tape are different depending on what you're playing it back with. I once was able to use that random fact to restore some data off an old floppy - it took three drives/PCs, but I was able to get a clean read of each block, and piece them together.

Extending that to DV tapes: the DV format is interesting in that every frame is a keyframe, and encodes an entire image. That's in contrast to H.264 and friends, where frames can be predicted, and/or just the difference between a prior and future frame can be encoded. DV also encodes a timecode into each frame. So if you had multiple DV decks and were able to get a bunch of unclean imports, it seems like it'd be trivial to write a small tool that grabs all of the clean frames from each and stitches them together over the gaps in others, according to that timecode.

(Disclaimer: I've never done that, this is a pure spitball.)

This is really interesting and not something I was aware of. (Although now the fact that an hour of MiniDV footage is 12GB makes more sense!).

I wonder if this is what DV Rescue (linked in my above post) is doing? If it's not doing this, it's certainly something that it should be doing.

You're also 100% spot on with the idea of using different drives to recover "tricky" tapes - I have two MiniDV camcorders exactly for that purpose. But I was doing it the "long" way of trying a tape in one, and if it didn't work well, trying it in the other. It didn't occur to me that I could try combining the results of both.

DVRescue sounds promising — thank you. From https://github.com/mipops/dvrescue

> dvmerge A script that takes multiple transfers of the same tape containing errors and combines them to create one file with the best information available for each problematic frame. dvmerge is part of dvrescue. See dvrescue -h on a recent build.

> dvplay A script that plays back and visualizes the DV errors as a stack of images. Running with the -x flag will produce JPEGs instead of just playing them.

> Snapshot daily builds are at https://mediaarea.net/download/snapshots/binary/dvrescue/.

Thank you, this is very helpful.

I have a hundred or so MiniDV tapes awaiting ingestion...first need to figure out where to store the data.

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