[mythtv-users] Some Videos Not Seen by Scan

[Mark Goldberg]

On Aug 10, 2017,  "Michael T. Dean" wrote:
>
> On Wed, Aug 9, 2017 at 5:55 AM, Dan Wilga wrote:
> On 08/09/2017 05:05 PM, Mark Perkins wrote:
> > On 10 August 2017 12:01:01 am "Michael T. Dean" wrote:
> >
> >> On 08/09/2017 10:04 AM, John Pilkington wrote:
> >>> Or search 'mythtv video hash'
> >>>
> >>> Perhaps your ffmpeg processes gave identical results.
> >> Yes, this is most likely the issue. The hash that's created to identify
> >> unique videos is done with only a small part of the file at the
> >> beginning and the end (because reading multiple gigabytes per file from
> >> disk and running the entire video through a hash algorithm would take
> >> ages to complete). It's likely your test files are just too close to
> >> the same, so are being considered the same and only showed once (one or
> >> the other is shown and the one not shown is ignored).
> >>
> >> There's no way to "fix" this as it's working as designed (and typical
> >> use cases don't involve multiple almost identical files).
> > I wonder if the hash algorithm could be updated to include the file
> > creation date or something else similar to help mitigate this type of
overlap?
>
> We're using the same hash algorithm used by other projects, the
> OpenSubtitles hashing algorithm, which is based on Media Player Classic.
> http://trac.opensubtitles.org/projects/opensubtitles/wiki/HashSourceCodes
>
> Any changes make ours a custom hash, with custom bugs and custom testing
> and custom maintenance required. It's also quite possible that some
> people are using the hash with other programs.
>
>
>

I checked the files and they are, in fact, identical, despite using
different command options to ffmpeg. So, I suppose there is not really a
big issue. Thanks for pointing out the hash algorithm, at least it is not a
mystery to me any longer.

Mark
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