I can't figure out how to add a custom line.
Edit the view scheme (I've assumed you know how, just ask if I've assumed too much, it won't be a problem) then click on the 'add rule' button, then type your rule into the field without selecting anything from the drop down on the left. Like so:
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If I've understood correctly, you're stacks are a mess, which is one problem, plus you have deleted files that were in stacks which has left debris behind.
Perhaps it might be an idea to start over...
If you specified a single directory for your cache conversion files, then the simplest option is to go there using windows explorer and delete that directory. MC's auto import will then take care of the housekeeping and tidy up your library.
If the files are 'beside the originals', there's a bit more work to do...
Make your custom rule: -[stack top]=-1 ~sort=[name],[stack top]-d
This will ensure that you're only dealing with files that are currently in stacks, and that when expanded, the stacks will stay together in the list.
When you're done with that, make sure you are in panes view up top, and details view down below.
Make sure the following columns are on view in the file list: "Stack Icon", "Stack Tag", "Name" and "Filename".
If any are missing, right click a column header in the file list and hover over columns. From the flyout list, click those that are missing to add them.
You can then drag and drop the column headers so as to place the four columns beside each other.
Now, with nothing selected, hover your mouse over the header where it says 'Pane' and a menu will show. Choose Options > Expand Stacks
All your stacks should now be expanded and you should be looking at a list full of something like this:
The "HH Conversion" files are mp3s in the ipod cache folder, the other two are the original flac files.
Try one or two first, but you should be able to select the HH Conversion files and delete them permanently.
Once you're happy, click on the "Stack Tag" column header to sort by it, select all the HH Conversion files and nuke 'em.
Don't freak out if you're left with an empty file list.Remember, you specified -[stack top]=-1 in the view scheme rules, and if MC has done its job correctly, there won't be any stacks left in your library, so the list should be empty.
Next time you connect your hand held player, go to options and set some rules for it.
I personally think it makes a lot more sense to have the cache files in their own directory out of the way somewhere. If you agree with me, tell MC where to put them, adding any library fields you need.
For example, mine go to: D:\iPod Cache\[media type]\[album artist (auto)]\[album]
Once set, you should have the same seamless functionality as the old style cache, with the big difference being, if you expand the stacks, all the cache mp3 files will become visible in your library just like any other files.
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If you need to track down any other 'orphan' mp3 cache files that have been left behind, you will need to think about your filing structure and library structure and work out some logical way to get MC to list the orphans.
Ideally, you're library is 100% flac files, therefore any mp3's can be deleted, so you would get MC to show you all mp3 files and then delete them.
If it's not as simple as that, what do you have to work with?
If needed, I can help you with any search rule you might need, but would need more information regarding your file system habits etc.
-marko.