Some video cannot play in macbook pro

What do you mean by 'before'? Have you upgraded the OS, just installed 10.10 from an earlier OS or installed a VLC update etc? It helps to know what changed besides this issue.

Quicktime X (the version that ships with 10.10) has limited or no support for a lot of video formats such as AVI & FLV - it may be normal that Quicktime X can't play those files (some may be converted if they can be opened). Quicktime 7 may still be able to play them, but support for that has been dropped…

QuickTime Player 7 for Mac OS X v10.6.3 or later

VLC should play more formats, what happens when you open the files in VLC? Open the 'Errors & warnings' window in VLC via the Window menu. Report what is listed when opening a bad file.

Do the files appear OK, does the size look correct if you get info on them in Finder via 'File > Get info'. Do you have read access to the files?

Re-read what I posted about the errors & warning window. That will give us a clue about why the file fails to play.

You need to open a file & then look at the errors.

VLC should list the errors in that window as the file fails to open.

VLC is a good player that handles a wide range of formats, there are others but frankly VLC is most likely to support the most common formats.

Mediainfo will list various info about the file format but that won't really explain why it suddenly stopped working.

https://mediaarea.net/en/MediaInfo

It may be simplest to reinstall VLC if you suspect that could be the issue.

There are older versions available for download too, see the link at the bottom of the downloads page…

http://www.videolan.org/vlc/download-macosx.html

Older versions can be found by browsing our our FTP archive

The one on the left also has a preview which indicates the file can be read. That may explain why that file has the 'more info' section.

Do you have a bootable backup of the OS before it was updated? That could be used to see if these files are still readable. It is possible that the files are damaged or it could simply be an issue with the OS.

Is VLC's error window given any info at all when you try to play any files?

You can still try using Quicktime, but that may be less likely to play certain formats (unless you know these files did work in Quicktime).

I'd suggest you try a new user account to see if there is some issue with your own account. Copyt some sample files into /Users/Shared so that both users can access them. Create a new user account in 'System Preferences > Users & groups', logout of your own account & then try playing the files when logged in as the new test user.

It's good that you tried the other computer, that rules out this Mac, it's updates & the user account. I'm afraid it sounds like these files are damaged or the disk could be failing.

Restart into recovery mode & use Disk Utility to check the disk, open the first aid tab and run verify & repair to see if there are errors reported. If there are any try to make a note, especially if they fail to repair (photograph the screen if you have to do so).

Do the backup copies work on the other computer?