OK so here is the log.
However whats I did notice is that if I started playing the video then switched the quality that after between 20 to 45 seconds the video would start playing normally, if I then moved the slider back to the start then the video would play without issue. The same result was seen for both 720p60 and 1080p60 videos.
03/06/2015 11:12:42.322 storeaccountd[1122]: AccountServiceDelegate: Accepting new connection <NSXPCConnection: 0x7fef98e6c500> connection from pid 4151 with interface <AccountServiceInterface: 0x7fef98d3c920> (PID 4151)
03/06/2015 11:12:42.405 com.apple.xpc.launchd[1]: (com.apple.imfoundation.IMRemoteURLConnectionAgent) The _DirtyJetsamMemoryLimit key is not available on this platform.
03/06/2015 11:12:47.229 com.evernote.EvernoteHelper[1145]: AppleEvents: Send port for process has no send right, port=( port:3935/0xf5f rcv:1,send:0,d:0 limit:5) (findOrCreate()/AEMachUtils.cp #526) com.apple.main-thread
03/06/2015 11:12:47.318 com.evernote.EvernoteHelper[1145]: AppleEvents: Send port for process has no send right, port=( port:3935/0xf5f rcv:1,send:0,d:0 limit:5) (findOrCreate()/AEMachUtils.cp #526) com.apple.main-thread
03/06/2015 11:12:47.328 com.evernote.EvernoteHelper[1145]: AppleEvents: Send port for process has no send right, port=( port:3935/0xf5f rcv:1,send:0,d:0 limit:5) (findOrCreate()/AEMachUtils.cp #526) com.apple.main-thread
03/06/2015 11:12:47.364 com.evernote.EvernoteHelper[1145]: AppleEvents: Send port for process has no send right, port=( port:3935/0xf5f rcv:1,send:0,d:0 limit:5) (findOrCreate()/AEMachUtils.cp #526) com.apple.main-thread
03/06/2015 11:12:47.371 com.evernote.EvernoteHelper[1145]: AppleEvents: Send port for process has no send right, port=( port:3935/0xf5f rcv:1,send:0,d:0 limit:5) (findOrCreate()/AEMachUtils.cp #526) com.apple.main-thread
03/06/2015 11:12:47.516 locationd[289]: Couldn't find a requirement string for masquerading client /System/Library/PrivateFrameworks/Parsec.framework
03/06/2015 11:12:47.516 locationd[289]: could not get apple languages array, assuming english
03/06/2015 11:12:47.529 com.evernote.EvernoteHelper[1145]: AppleEvents: Send port for process has no send right, port=( port:3935/0xf5f rcv:1,send:0,d:0 limit:5) (findOrCreate()/AEMachUtils.cp #526) com.apple.main-thread
03/06/2015 11:12:47.530 com.apple.xpc.launchd[1]: (com.apple.imfoundation.IMRemoteURLConnectionAgent) The _DirtyJetsamMemoryLimit key is not available on this platform.
03/06/2015 11:12:47.577 2BUA8C4S2C.com.agilebits.onepassword4-helper[1139]: 532001 [EXT:0x7fa6fb51f800:<OP4ExtensionHTTPConnection: 0x7fa6f9e7cd10>] M webSocketForURI: | [ES4] Extension connected Safari-Extension 'safari-extension://com.agilebits.onepassword4-safari-2bua8c4s2c / (null)'
03/06/2015 11:12:54.378 com.apple.xpc.launchd[1]: (com.apple.imfoundation.IMRemoteURLConnectionAgent) The _DirtyJetsamMemoryLimit key is not available on this platform.
03/06/2015 11:12:56.775 com.apple.xpc.launchd[1]: (com.apple.imfoundation.IMRemoteURLConnectionAgent) The _DirtyJetsamMemoryLimit key is not available on this platform.
03/06/2015 11:12:58.999 com.apple.Safari.SearchHelper[4163]: Failed to obtain sandbox extension for path=/Users/USERNAME/Library/Caches/com.apple.Safari.SearchHelper. Errno:1
03/06/2015 11:12:59.005 com.apple.Safari.SearchHelper[4163]: Failed to obtain sandbox extension for path=/Users/USERNAME/Library/Caches/com.apple.Safari.SearchHelper. Errno:1
03/06/2015 11:12:59.165 com.apple.SecurityServer[81]: Session 100097 created
03/06/2015 11:13:00.641 sandboxd[474]: ([4163]) com.apple.Safari(4163) deny file-issue-extension /Users/USERNAME/Library/Caches/com.apple.Safari.SearchHelper
03/06/2015 11:13:00.795 sandboxd[474]: ([4163]) com.apple.Safari(4163) deny file-issue-extension /Users/USERNAME/Library/Caches/com.apple.Safari.SearchHelper