SL2-S video file - unusual error

[LocalHero1953]

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TL/DR: has anyone ever had a problem with a single frame within a clip causing an error message at the time of rendering? And is there a way of checking clips for such errors before a lengthy render?

I recorded an outdoor drama production last week. The SL2-S was set on a tripod with the 16-35SL lens on fixed focus. The camera was connected to mains power by USB, and I recorded to two pairs of Sandisk Extreme Pro 128Gb 300Mb/s V90 UHS-II cards. The format was C4K 25fps, .mov, ALL-I, L-Log. I used the setting that recorded 1 minute files (and had 100+ such clips). My Sigma fp recorded other footage with a long lens to be added to the final production. The final output was to be at HD, allowing some virtual zooming and panning within the C4K frame in editing.

I edited in Davinci Resolve 17, created optimised media, checked and made edits to the colour of the 1 minute clips, then created compound clips for each half of the performance. I then edited in the zooming and panning effects, added other clips as different tracks etc etc and tried to create a final render.

It produced an error at the same point every time, stating that a particular named 1 minute clip could not be rendered and I should check the original file still existed. After decomposing the compound clip and trying to render the erroneous one on its own, I spotted one frame that would not display ("media missing"). Cutting out this frame allowed the whole clip and the final video to render just fine.

Needless to say this took me (an inexperienced video editor) the best part of 6 hours to track down, including redoing all my colour grading, panning and zooming edits, and getting to bed at 1.30am.

Any advice on my original questions would be welcome!

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[Photoworks]

Sounds to me more like a software issue, maybe an issue in optimized media.

Di you go back to the card to check the file on the SD card?

[LocalHero1953]

52 minutes ago, Photoworks said:

Sounds to me more like a software issue, maybe an issue in optimized media.

Di you go back to the card to check the file on the SD card?

I went back to the original file on my hard disk and played it in VLCC - the problem showed also there, so it wasn't just in the optimised media. I had already formatted and overwritten the SD card by that time. I have nothing to suggest it is a SL2-S issue rather than SD card (or anything else), but I posted here in case anyone else had ever experienced something similar. I was relieved that in 100+ files from the same recording, there was only this single frame error.

Edited July 15, 2022 by LocalHero1953

[BernardC]

1 hour ago, LocalHero1953 said:

I went back to the original file on my hard disk and played it in VLCC - the problem showed also there, so it wasn't just in the optimised media.

Optimized media is used for faster editing, but Resolve goes back to the source files for rendering.

One additional thing to try is checking the file on your SD card, if it hasn't been re-formated. It could be a copy error.

[hansvons]

This happens. But it's not a regular incident. Often, the embedded sound is the culprit. Back in the day, such erroneous/corrupt files could corrupt complete editing projects. I saw this a dozen times in, say, ten years of video editing and compositing (approx 50 days per year, ten projects). 
 

As Bernard suggests, checking the original file on the SD card might be worthwhile.

If that happens repeatedly again (which is unlikely), I’d bin the SD card. 

Editing faulty files before ingesting them in the NLE by cutting off the problematic part is good practice. You can do that with Keyno by re-wrapping only the clip’s good parts in a new container. Or, you do that using an transcoding software that allows editing and transcoding to a codec with higher fidelity.

[LocalHero1953]

I found the original file on SD card - it was not a card I had already reused.

• I recopied it to hard disk (internal SSD) under a new name, and imported it to a new Davinci project: there was no faulty frame.
• I went back to the file as copied to hard disk a week ago, imported it to the same new project: it contained the faulty frame.
• Copied that same file from SSD to a new folder under a new name (to avoid Davinci linking it to a conformed version). Imported it to the new project - it still had the faulty frame. 

Conclusion: it acquired the faulty frame when I first copied it from SD card to hard disk.

If the same thing happens again, at least I should be able to track the error down more quickly.

And, to ask again one of my original questions: is there a quick way of finding frame errors in clips (i.e. 'validating' clips) before getting to the final render (as I did!)?
Edit: Sorry, I've just seen @hansvonssuggestions, which I will follow up.

Edited July 17, 2022 by LocalHero1953

[BernardC]

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2 hours ago, LocalHero1953 said:

And, to ask again one of my original questions: is there a quick way of finding frame errors in clips (i.e. 'validating' clips) before getting to the final render (as I did!)?

There are utilities that will verify the integrity of your media backups. These are used by digital imaging technicians (DITs) on-set.They wouldn't help if your files were corrupted in-camera, but they would help in a case like yours.

ShotPut Pro is one of the more common packages. There are others, including free ones like Pomfort SealVerify. The applications basically run checksums on your originals and copies, and keeps a database of these. They also allow you to set-up "one button" backup tasks, so you can copy files to multiple locations.

 

[beewee]

If you want to mirror folders and compare files at a binary level, I highly recommend Beyond Compare for Windows/Mac/Linux. I use it for non-photography related work and it’s extremely fast and very easy to use. For anyone that codes, you’ll know what I mean when I say it’s like the Notepad++ of file syncing tools.