user30031: I back up my data to pairs of external hard drives, and recently (in the process of transferring the contents to larger external hard drives) found that some of the data between them has diverged. Several of them are video files.
I used this answer to use ffmpeg's ssim and psnr filters to find the differences between the two videos. Once I had a location, I loaded the tracks into kdenlive, applied the "difference" transition, and seeked to the area where the difference was.
However, no difference was to be seen! I even extracted the audio, and used audacity to compare differences, and still nothing.
The files are clearly different; ffmpeg shows that. But if I can't see any differences, I don't know which file to copy over the other file.
Any idea what I could be doing wrong? This seems too simple to fail.

user3592: Use a vector scope and waveform monitor to judge the difference, not your eyes.  Even if you're doing an XOR comparison, there are cases where your eye isn't enough.
Here, for example, I've taken this sample footage from BMD's SDK (available here):
 The original is 12bit RAW.  I then transcoded it to H.265, using these settings:

If I then superimpose the transcoded version over the original, like this:

... and set the blending mode to "difference," a.k.a., "XOR"

and then use the scopes to analyze the result, you can clearly see that the files are different.

The top half of the above image shows the timeline viewer, and the result of the "difference" comparison.  To the naked eye, it looks black, as if there is no difference.  The bottom half of the above image shows Resolve's waveform monitor.  Here's a detail of that same image:

There's clearly noise at the bottom end of the signal.  Other types of scopes will tell you different information about the comparison.  For instance, you can use a parade to examine Y'CbCr, and see that the transcode operation has affected the image's chroma more than its luma.   
I know that you're trying to examine the difference between files that you've copied and not necessarily transcoded, but this example is meant to demonstrate that scopes can give you insight into the type of difference between the files, when that difference is invisible to the naked eye.

30031: <p>I back up my data to pairs of external hard drives, and recently (in the process of transferring the contents to larger external hard drives) found that some of the data between them has diverged. Several of them are video files.</p>
<p>I used <a href="https://stackoverflow.com/a/33567032/603828">this answer</a> to use ffmpeg's ssim and psnr filters to find the differences between the two videos. Once I had a location, I loaded the tracks into <a href="https://kdenlive.org/" rel="nofollow noreferrer">kdenlive</a>, applied the &quot;difference&quot; transition, and seeked to the area where the difference was.</p>
<p>However, no difference was to be seen! I even extracted the audio, and used audacity to <a href="https://forum.audacityteam.org/viewtopic.php?t=525" rel="nofollow noreferrer">compare differences</a>, and still nothing.</p>
<p>The files are clearly different; ffmpeg shows that. But if I can't see any differences, I don't know which file to copy over the other file.</p>
<p>Any idea what I could be doing wrong? This seems too simple to fail.</p>
 3592: <p>Use a vector scope and waveform monitor to judge the difference, not your eyes.  Even if you're doing an XOR comparison, there are cases where your eye isn't enough.</p>
<p>Here, for example, I've taken this sample footage from BMD's SDK (available <a href="https://www.blackmagicdesign.com/support/" rel="nofollow noreferrer">here</a>):
<a href="https://i.stack.imgur.com/8u8aV.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8u8aV.jpg" alt="enter image description here" /></a> The original is 12bit RAW.  I then transcoded it to H.265, using these settings:
<a href="https://i.stack.imgur.com/0CoY2.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0CoY2.jpg" alt="enter image description here" /></a>
If I then superimpose the transcoded version over the original, like this:
<a href="https://i.stack.imgur.com/LH0FW.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LH0FW.jpg" alt="enter image description here" /></a>
... and set the blending mode to &quot;difference,&quot; a.k.a., &quot;XOR&quot;
<a href="https://i.stack.imgur.com/gSA2V.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gSA2V.jpg" alt="enter image description here" /></a>
and then use the scopes to analyze the result, you can clearly see that the files are different.
<a href="https://i.stack.imgur.com/6sQBT.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6sQBT.jpg" alt="enter image description here" /></a>
The top half of the above image shows the timeline viewer, and the result of the &quot;difference&quot; comparison.  To the naked eye, it looks black, as if there is no difference.  The bottom half of the above image shows Resolve's waveform monitor.  Here's a detail of that same image:
<a href="https://i.stack.imgur.com/MRCz3.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MRCz3.jpg" alt="enter image description here" /></a>
There's clearly noise at the bottom end of the signal.  Other types of scopes will tell you different information about the comparison.  For instance, you can use a parade to examine Y'CbCr, and see that the transcode operation has affected the image's chroma more than its luma.   <a href="https://i.stack.imgur.com/RKqQT.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RKqQT.jpg" alt="enter image description here" /></a></p>
<p>I know that you're trying to examine the difference between files that you've <em>copied</em> and not necessarily <em>transcoded</em>, but this example is meant to demonstrate that scopes can give you insight into the type of difference between the files, when that difference is invisible to the naked eye.</p>
