[I am a GCI student]

If I understand you right you think it is a dolphin bug. Please, report it as such. Could you try installing your xfce file viewer and video player and test with those on your kubuntu machine? And try installing dolphin on your xubuntu machine?

And do this: Sehen Sie für Details im Fehlerprotokoll nach.

Created attachment 90137 [details]
the log from vlc in case of the error (2 trials)

I tried some cases:

- its not a problem with rights (samba or filesystem) (copy is possible, other systems are OK)
- ist not a performanceproblem, because all tests are made on the same hardware (errors and OKs)
- renamed the file to play to aa.mp4 (to make shure, there‘s no name problem with spaces or other language-typical signs) - same result

testet with kubuntu and krusader: error (the same)
testet with xubuntu and thunar: all OK
testet with xubuntu and nemo: all OK
on the same Xubuntu-machine: 
startet vlc (empty) > open file > go to a mp4-file on the nas > play >>> works
(no idea, what file-dialog it is)

next: installed dolphin in my xubuntu 14.04    

start dolphin > browse to the networkfolder > right mouse on mp4-file > play with vlc
Error (the same like i have seen everytime)

start dolphin > browse to the networkfolder > right mouse on mp4-file > play with Parole Media player
!! it copies the file to /var/temp/... anr when ready > it plays the file without problems!!
(not I have initiatet the file copy, it makes it automatically)

(copy before play (with manually works also in dolphin) is not a solution, because the Fritzbox NAS copies with about 2 Mbit/s)

I dont think it's a dolphin problem because krusader didn't work allso.
Mp3-files or pictures work in dolphin over the same share with the same kind of file-access.
( right mouse > open with)
Other Players do allmost the same. (cannot see errormessages, but no file played, no reaction)

I am unsure which users you are setting up to log into the samba share. Comment #0 says it is "freitag@fritzbox", while comment #2 says "rudi@192.168.178.1", and fails with

access_smb error: open failed for 'rudi@192.168.178.1/fritzbox/Kingston-DataTraveler2-0-01/joe%20bonamassa%20-%20royal%20albert%20hall.mp4' (Permission denied)

Where does the "rudi" name come from?

The NAS knows -among others- both users: freitag and rudi, both have a uniqe password. 
both users are allowed full r/w on the share.  

KUBUNTU uses the kdewallet witch icludes two users for destination 192.168.178.1:
login > rudi with its password
login-2 > freitag with its password
rudi also is the name of my user in kubuntu (local) 
when i went (with dolphin) to the share, it asked me for the passwort of the wallet.
(its the local password from rudi, btw the same as the NAS-password) 
This password opens the wallet (i think) and then transfers the logindata to the NAS.
No idea what else happens...

When i use Xubuntu, theres no wallet - i believe. Whe the filemanager asks, i give the NAS-Password directly.

cleared - for test reasons - the wallet: 
now its no access to the share possible:

dolphin > network it shows:
-samba shares > it shows 2 "workgroups": workgroup and Yello (this is ok and intended)
-network: nothing happens
-network services: nothing happens
-MTP devices 

the NAS is in YELLO
when i try to access, it asks fo username and password only (xubuntu asks also for Group)
i give the login datas and.... the autheticationdialog apears again and again and again... loop
(testet with both logins)  
this is new. untill now i was able to browse tghe NAS without difficulties.
Tomorrow i will further search for the reasons...

Thanks for the investigation so far. Reassigning to kio-smb developers. They might better understand what you wrote.

would you please reassign this note to the developer? thanks.

Now:
I renamed the workgroup name of the fritzbox from yello to workgroup to minimize sideeffekts.
Then I renewed the share and the users of the fritzbox.
Testet the share fom xubuntu and kubuntu > both OK.

Startet thunar/nemo from _X_ubuntu > browse to share > right mouse to moviefile > play with vlc > both times OK.

Now the other way round: 

startet _K_ubuntu, tested share with copy: OK
installed nemo and thunar on Kubuntu

startet thunar from Kubuntu > browse to share > right mouse to moviefile > play with vlc > error

---------------------------------------------------------------------------------------------------
this is what thunar sayed on commandline:  

rudi@Musikubu1404:~$ thunar

Your Thunar settings have been migrated to Xfconf.
The config file "/home/rudi/.config/Thunar/thunarrc"
is not used anymore.

(thunar:4050): GLib-CRITICAL **: Source ID 553 was not found when attempting to remove it
(thunar:4050): GLib-CRITICAL **: Source ID 761 was not found when attempting to remove it
(thunar:4050): GLib-CRITICAL **: Source ID 853 was not found when attempting to remove it
(thunar:4050): GLib-CRITICAL **: Source ID 946 was not found when attempting to remove it
(thunar:4050): GLib-CRITICAL **: Source ID 1624 was not found when attempting to remove it
(thunar:4050): Gdk-CRITICAL **: IA__gdk_window_get_window_type: assertion 'GDK_IS_WINDOW (window)' failed
VLC media player 2.1.4 Rincewind (revision 2.1.4-0-g2a072be)
[0xeeb118] main libvlc: VLC wird mit dem Standard-Interface ausgeführt. Benutzen Sie 'cvlc', um VLC ohne Interface zu verwenden.
[0x7f004c001308] access_smb access error: open failed for 'fritzbox/fritzbox/Kingston-DataTraveler2-0-01/Einsfestival-Sound_City_-_Teil_1-393879_3939610.mp4' (Permission denied)
[0x7f005c000a68] main input error: open of `smb://fritzbox/fritzbox/Kingston-DataTraveler2-0-01/Einsfestival-Sound_City_-_Teil_1-393879_3939610.mp4' failed
Bus::open: Can not get ibus-daemon's address. 
IBusInputContext::createInputContext: no connection to ibus-daemon 

(thunar:4050): GLib-CRITICAL **: Source ID 1747 was not found when attempting to remove it
rudi@Musikubu1404:~$ 
--------------------------------------------------------------------------------------------------
next trial with nemo:

Startet nemo from kubuntu > browse to share > right mouse to moviefile > play with vlc > error

and the commandline-output from nemo:
rudi@Musikubu1404:~$ nemo
(nemo:4205): GLib-CRITICAL **: g_strrstr: assertion 'haystack != NULL' failed
(nemo:4205): GLib-CRITICAL **: g_strrstr: assertion 'haystack != NULL' failed
(nemo:4205): GLib-CRITICAL **: g_strrstr: assertion 'haystack != NULL' failed
(nemo:4205): GLib-CRITICAL **: g_strrstr: assertion 'haystack != NULL' failed
(nemo:4205): GLib-CRITICAL **: g_strrstr: assertion 'haystack != NULL' failed
(nemo:4205): GLib-CRITICAL **: g_strrstr: assertion 'haystack != NULL' failed
(nemo:4205): GLib-CRITICAL **: g_strrstr: assertion 'haystack != NULL' failed
VLC media player 2.1.4 Rincewind (revision 2.1.4-0-g2a072be)
[0xfc4118] main libvlc: VLC wird mit dem Standard-Interface ausgeführt. Benutzen Sie 'cvlc', um VLC ohne Interface zu verwenden.
[0x7f8150000ff8] access_smb access error: open failed for 'fritzbox/fritzbox/Kingston-DataTraveler2-0-01/ForeverYoung.mp4' (Permission denied)
[0x7f81540009b8] main input error: open of `smb://fritzbox/fritzbox/Kingston-DataTraveler2-0-01/ForeverYoung.mp4' failed
Bus::open: Can not get ibus-daemon's address. 
IBusInputContext::createInputContext: no connection to ibus-daemon 

-----------------------------------------------------------------------------------------------------

short summary:

from XFCE 
- it works with nemo and thunar and from inside vlc (open file....)
- errors when i use dolphin

from KDE
- errors with dolphin, thunar, nemo and krusader.

copy and write operations are possible with all systems: windows xp/7, android, Xubuntu, Kubuntu. 
The problem only exists with video-files: avi, mp4, webm, divX, flv ... 
mp3, jpg etc are all working. (dolphin.. browse share > right mouse > open with.. OK) 

unclear:
in some cases, after a trial whitch leads to an error, i'm not able to go to the share within dolphin.
I cannot even see the share, share-bookmarks are not working, dolphin shows a red errormessage on top.
Sorry for not remebering - something like: there's no share with the name ....
Just now i am not able to reproduce this. 
Made a restart and the share works again.

supplement & error correction

I installed 2 more Systems: kubuntu and ubuntu studio (xubuntu) 14.04.1 to test.
Used Kubuntu Backorts an another Systems: all systems showed the same behavior like described above. 

But:
I probed with another NAS. Used an AMS150 from Fujitsu Siemens and a SMB share.
And it worked! with vlcplayer also in Kubuntu. 
another thing:the (default) Dragonplayer sayes "SMB protocol source" plugin is needed. (Download yes/no solved/found nothing)

Suppost the problem only seams to exist with a share on the Fritz.box at first 
Its a 7390, probed Firmware 6.20 & 6.23 
http://avm.de/produkte/fritzbox/fritzbox-7390/technische-daten/  )

Then I testet once again from Android 4.4 and found a mistake in my description

Result against Fritz box share: 
works with MX player and ES video player, did not play with vlc player and LIVE player (no idea what it is)

result against AMS150 share with video files:
mx player - works
es player - works after caching
Google video player, vlc player - no reaction
(both tested with h264 kompressed mp4 files)

renewed windows-test: worked with vlc and both networkdestinations (ams150 & fritztbox) 

Conclusion:now i have no idea what is the cause of the problem:
kde / player / smb(client?) / fritzbox / me? ...confused

Duplicate of Bug 355328. In essence, the problem is that KIO doesn't actually mount Samba shares anywhere like GNOME's GVFS does (maybe XFCE has some equivalent or uses the same thing?). As a result, all applications that wish to access files on password-protected Samba shares must use KIO. With non-KIO-aware software, KIO falls back to passing them a URL that doesn't include a password in it, and thus the program itself must implement a samba client for access and look up the missing credentials in KWallet.

I am in the process of helping the VLC folks implement this. See:
- https://trac.videolan.org/vlc/ticket/18993
- https://trac.videolan.org/vlc/ticket/18991

*** This bug has been marked as a duplicate of bug 355328 ***

*** This bug has been marked as a duplicate of bug 330192 ***

*** This bug has been marked as a duplicate of bug 75324 ***