Thank you very much Old Toad. As an addendum, after I posted my question, I imported some of the files into FCP, and the clips all played and burned normally, which is ultimately what I'm looking for. Obviously a problem with iPhoto. Anyway, here is the results from Etrecheck. Thanks again for your help.
EtreCheck version: 2.9.12 (265)
Report generated 2016-05-14 19:51:42
Download EtreCheck from https://etrecheck.com
Runtime 3:10
Performance: Good
Click the [Support] links for help with non-Apple products.
Click the [Details] links for more information about that line.
Click the [Remove] links to remove adware.
Problem: Other problem
Description:
Imported video clips from iPhone 6s judders in iPhoto.
Hardware Information:ⓘ
iMac (21.5-inch, Mid 2011)
[Technical Specifications] - [User Guide] - [Warranty & Service]
iMac - model: iMac12,1
1 2.5 GHz Intel Core i5 CPU: 4-core
4 GB RAM Upgradeable - [Instructions]
BANK 0/DIMM0
2 GB DDR3 1333 MHz ok
BANK 1/DIMM0
2 GB DDR3 1333 MHz ok
BANK 0/DIMM1
Empty
BANK 1/DIMM1
Empty
Bluetooth: Old - Handoff/Airdrop2 not supported
Wireless: en1: 802.11 a/b/g/n
Video Information:ⓘ
AMD Radeon HD 6750M - VRAM: 512 MB
iMac 1920 x 1080
System Software:ⓘ
OS X Mavericks 10.9.5 (13F1712) - Time since boot: about 5 days
Disk Information:ⓘ
ST3500418AS disk0 : (500.11 GB) (Rotational)
EFI (disk0s1) <not mounted> : 210 MB
Macintosh HD (disk0s2) / : 499.25 GB (78.36 GB free)
Recovery HD (disk0s3) <not mounted> [Recovery]: 650 MB
OPTIARC DVD RW AD-5690H ()
USB Information:ⓘ
Apple Inc. FaceTime HD Camera (Built-in)
Apple Inc. BRCM2046 Hub
Apple Inc. Bluetooth USB Host Controller
Apple Internal Memory Card Reader
Apple Computer, Inc. IR Receiver
Thunderbolt Information:ⓘ
Apple Inc. thunderbolt_bus
Gatekeeper:ⓘ
Mac App Store and identified developers
Adware:ⓘ
~/Library/Caches/com.apple.Safari/Extens...safariextension
~/Library/Caches/com.apple.Safari/Extens...safariextension
~/Library/Caches/com.apple.Safari/Extensions/Searchme.safariextension
~/Library/Caches/com.apple.Safari/Extensions/Slick Savings.safariextension
~/Library/Caches/com.apple.Safari/Extens...safariextension
~/Library/LaunchAgents/com.spigot.ApplicationManager.plist
~/Library/Safari/Extensions/Searchme.safariextz
~/Library/Safari/Extensions/Slick Savings.safariextz
~/Library/Safari/Extensions/eBay Shopping Assistant.safariextz
9 adware files found. [Remove]
Kernel Extensions:ⓘ
/Applications/Toast 11 Titanium/Spin Doctor.app
[not loaded] com.hzsystems.terminus.driver (4 - 2013-02-01) [Support]
/Library/Extensions
[loaded] com.Perfect.Driver.SystemAudioRecorder (1.1.0 - SDK 10.9 - 2016-03-30) [Support]
/System/Library/Extensions
[loaded] com.InnovationTechnology.driver.ComputerAudio (1.01 - SDK 10.7 - 2016-05-11) [Support]
[loaded] com.globaldelight.driver.BoomDevice (1.1 - SDK 10.1 - 2016-05-11) [Support]
[loaded] com.logmein.driver.LogMeInSoundDriver (4.1.6547 - 2016-05-11) [Support]
[not loaded] com.roxio.BluRaySupport (1.1.6 - 2016-05-11) [Support]
[not loaded] com.seagate.driver.PowSecDriverCore (5.2.4 (26840) - SDK 10.4 - 2016-05-11) [Support]
/System/Library/Extensions/Seagate Storage Driver.kext/Contents/PlugIns
[not loaded] com.seagate.driver.PowSecLeafDriver_10_4 (5.2.4 (26840) - SDK 10.4 - 2014-03-25) [Support]
[not loaded] com.seagate.driver.PowSecLeafDriver_10_5 (5.2.4 (26840) - SDK 10.5 - 2014-03-25) [Support]
[not loaded] com.seagate.driver.SeagateDriveIcons (5.2.4 (26840) - SDK 10.4 - 2014-03-25) [Support]
~/Library/Services/ToastIt.service/Contents/MacOS
[not loaded] com.roxio.TDIXController (2.0 - 2016-04-09) [Support]
System Launch Agents:ⓘ
[not loaded] 6 Apple tasks
[loaded] 133 Apple tasks
[running] 45 Apple tasks
System Launch Daemons:ⓘ
[not loaded] 50 Apple tasks
[loaded] 131 Apple tasks
[running] 68 Apple tasks
Launch Agents:ⓘ
[failed] com.adobe.ARMDCHelper.cc24aef4a1b90ed56a...plist (2016-05-11) [Support]
[failed] com.logmein.LMILaunchAgentFixer.plist (2016-05-11) [Support]
[running] com.logmein.logmeingui.plist (2016-05-11) [Support]
[running] com.logmein.logmeinguiagent.plist (2016-05-11) [Support]
[not loaded] com.logmein.logmeinguiagentatlogin.plist (2016-05-11) [Support]
Launch Daemons:ⓘ
[running] com.adobe.ARMDC.Communicator.plist (2016-05-11) [Support]
[running] com.adobe.ARMDC.SMJobBlessHelper.plist (2016-05-11) [Support]
[failed] com.adobe.fpsaud.plist (2016-04-15) [Support]
[failed] com.edovia.screensconnect.daemon.plist (2012-03-12) [Support]
[running] com.logmein.logmeinserver.plist (2016-05-11) [Support]
[not loaded] com.logmein.raupdate.plist (2012-07-30) [Support]
[loaded] com.rogueamoeba.instanton-agent.plist (2014-03-25) [Support]
User Launch Agents:ⓘ
[loaded] com.adobe.ARM.[...].plist (2013-03-16) [Support]
[running] com.apple.FolderActions.enabled.plist
[loaded] com.apple.FolderActions.folders.plist
[loaded] com.google.keystone.agent.plist (2016-03-26) [Support]
[running] com.mlbam.nexdef.plist (2012-05-05) [Support]
[failed] com.rogueamoeba.loopbackd.plist (2016-03-08) [Support]
[loaded] com.shoebox.launched.plist (2015-10-10) [Support]
[loaded] com.shoebox.launched.pliste (2015-10-10) [Support]
[not loaded] com.spigot.ApplicationManager.plist (2016-03-03) Adware! [Remove]
~/Library/Application Support/Spigot/ApplicationManager
[loaded] uk.co.markallan.clamxav.freshclam.plist (2015-07-28) [Support]
User Login Items:ⓘ
iTunesHelper Application (/Applications/iTunes.app/Contents/MacOS/iTunesHelper.app)
Dropbox Application (/Applications/Dropbox.app)
Other Apps:ⓘ
[running] [0x0-0x2e42e4].com.azureus.vuze
[running] [0x0-0x3b33b3].com.etresoft.EtreCheck
[running] com.adobe.Reader.56352
[running] com.getdropbox.dropbox.28720
[loaded] 442 Apple tasks
[running] 446 Apple tasks
Internet Plug-ins:ⓘ
LogMeInSafari64: 1.0.660 (2012-03-20) [Support]
Unity Web Player: UnityPlayer version 4.0.0f7 (2013-11-29) [Support]
Default Browser: 537 - SDK 10.9 (2014-09-26)
AdobePDFViewerNPAPI: 15.016.20039 - SDK 10.11 (2016-05-11) [Support]
FlashPlayer-10.6: 21.0.0.226 - SDK 10.6 (2016-04-21) [Support]
LogMeIn: 1.0.660 (2012-04-06) [Support]
Silverlight: 5.1.10411.0 - SDK 10.6 (2012-06-22) [Support]
QuickTime Plugin: 7.7.3 (2016-03-30)
Flash Player: 21.0.0.226 - SDK 10.6 (2016-04-21) Outdated! Update
LogMeInSafari32: 1.0.660 (2012-03-20) [Support]
AdobePDFViewer: 15.016.20039 - SDK 10.11 (2016-05-11) [Support]
JavaAppletPlugin: 14.9.0 - SDK 10.7 (2014-06-20) Check version
User internet Plug-ins:ⓘ
BlueStacks Install Detector: Unknown
Dashlane: Dashlane 1.0.0 - SDK 10.10 (2014-12-09) [Support]
CitrixOnlineWebDeploymentPlugin: 1.0.105 (2013-04-25) [Support]
NPRoblox: 1.0.2.12 - SDK 10.8 (2013-08-01) [Support]
Safari Extensions:ⓘ
Amazon Shopping Assistant (cache only) (2014-05-21) Adware! [Remove]
Ghostery - GHOSTERY, Inc. - https://www.ghostery.com/ (2016-05-12)
eBay Shopping Assistant - Spigot, Inc. - http://www.mybrowserbar.com (2016-03-03) Adware! [Remove]
Ebay Shopping Assistant (cache only) (2014-05-21) Adware! [Remove]
Slick Savings (2016-03-03) Adware! [Remove]
AdBlock - BetaFish, Inc. - https://getadblock.com (2016-04-16)
Searchme - Spigot, Inc. - http://www.mybrowserbar.com (2016-03-03) Adware! [Remove]
3rd Party Preference Panes:ⓘ
AppTrap (2014-11-26) [Support]
Flash Player (2016-04-15) [Support]
Perian (2011-07-23) [Support]
Time Machine:ⓘ
Skip System Files: NO
Mobile backups: OFF
Auto backup: NO - Auto backup turned off
Volumes being backed up:
Macintosh HD: Disk size: 499.25 GB Disk used: 420.88 GB
Destinations:
Andy and Joy [Network]
Total size: 2.00 TB
Total number of backups: 1
Oldest backup: 3/29/16, 7:16 PM
Last backup: 3/29/16, 7:16 PM
Size of backup disk: Excellent
Backup size 2.00 TB > (Disk size 499.25 GB X 3)
Top Processes by CPU:ⓘ
20% com.apple.WebKit.Plugin.64
2% fontd
2% coreaudiod
1% WindowServer
1% kernel_task
Top Processes by Memory:ⓘ
508 MB com.apple.WebKit.WebContent(4)
463 MB kernel_task
221 MB Safari
172 MB com.apple.WebKit.Plugin.64
115 MB AdobeReader
Virtual Memory Information:ⓘ
245 MB Free RAM
3.00 GB Used RAM (822 MB Cached)
0 B Swap Used