[Craig Seeman]

First, professionally speaking, no one should be handing you m2t files without the complete container but, unfortunately there are people who do that.
I believe the products you describe are mostly front ends to ffmpeg encoders. They might be OK for sharing files but I wouldn’t use them in a serious post workflow where, if sources needed transcoding, I’d transcode to a flavor of Apple ProRes (some might use DNxHD on Windows). Or, if you want to avoid the transcode, rewrap the file in a .mov container.

You’d be better off using something like Divergent Media’s Edit Ready.

[Craig Seeman]

Recent versions of Compressor 4 can take advantage of Intel QuickSync (in i7 processors, not Xeon) for faster H.264 encoding. Also Apple’s H.264 encoding quality has greatly (and to me very significantly) improved over Compressor 3 series. Both these improvements are major.

[Craig Seeman]

Then your option would be aeroquartet or wait until you find someone in the UK. At some point this becomes a business decision on how badly you need the video and wait you’re willing to risk losing it.

[Craig Seeman]

Have you tested with VLC player?
If you can play the video there, you might be able re-encode (yes that would be lossy) with an ffmpeg encoder.
You may also went to test with the free Telestream Switch. If that plays the file then it might be worth it to pay for the higher end version to export/encode.

[Craig Seeman]

One of the most important aspects of XAVC-L is that it can be 10 bit 4:2:2 which allows for much more aggressive color grading, FX work, chroma keying as needed. It also allows for higher data rates (better potential quality) as the codec is less likely to have artifacts when compressing complex subjects.

One of Sony’s sites explains

What are the differences between XAVC and AVCHD?

XAVC format provides 4K/HD, 4:4:4/4:2:2/4:2:0 and 12/10/8 bit sampling which can cover a wide range of applications from professional to consumer products, from high-end 4K production through to online streaming and consumer imaging applications. AVCHD, by contrast, is capped at 24Mbps for 1080 50i/50i or 28Mbps for 1080 50P/60P at 4:2:0 8bit sampling and is fully compatible with the Blu-ray disc format. Both XAVC and AVCHD formats adopt the same MPEG-4 AVC/H.264 compression technology, but there is no compatibility between them.

[Craig Seeman]

AVCHD
It’s a file format based on AVC (H.264).
At the file system level, the structure of AVCHD is derived from the Blu-ray Disc specification, but is not identical to it.
The BDMV (Blu-Ray Disc Movie Video) directory contains media files.
The MTS file is the Media file (the container of the media itself) MPEG Transport Stream.

Open the AVCHD in Quicktime X and you’ll see your Clips if you recording in that mode.

If you’re using the camera in XAVC mode the MXF files are in PRIVATE > XDROOT > CLIP

[Craig Seeman]

[andy patterson] “Thunderbolt 2 is the same as PCIE 2.0 at four lanes. Many Graphics cards can exceed that. Thunderbolt 3 is better but the Mac Pro still does not have Thunderbolt 3.”

I think his point is that he can extend the life of his Mac Pro, not that it will match current technology.

[andy patterson] “Thunderbolt 3 is good but it does not have the same amount of bandwidth as PCIE 3.0 at 16 lanes. “

But perhaps there’s “good enough” for vast middle of niche market.

[andy patterson] “PC users can use Thunderbolt 3 as well so I don’t see your point or how you can do something I cannot.”

And PCs got there first this time. But depending on the number of devices you need to use and the need to move them from machine to machine, one may have a bit more flexibility given the number of ports.

[andy patterson] “Some things can be daisy chained others cannot because of bandwidth limitation of Thunderbolt 2. “

Which is why the number of ports is of value. A PC with one TB2 port will hit that limit sooner.
What happens with the next Mac Pro (if there is one) is speculative but my guess it’ll have multiple TB3 ports (and admittedly no idea how they’ll handle controllers/busses).

[andy patterson] “Even with Thunderbolt 3 you wouldn’t want to daisy chain two GTX 1080s. “

If there is a new Mac Pro I’m sure they’ll be multipole TB3 ports and value in daisy chaining.

[andy patterson] “All the PCs at the time of the Mac Pro 2013 had PCIE 3.0. Why not have PCIE and Thunderbolt 3? “

That would have been nice. I’m not sure the demand was there. It seems like a niche within a niche in the “professional” video market. The demand for high powered workstations is, at best stagnant. Apple is not pursuing that.

[andy patterson] “Having said that why would I want my graphics card outside of my computer? Why not just get an ITX case?”

Because you’d be able to move it from desktop to laptop as needed.

What does the median professional need? TB3 may be enough. Multiple TB3 ports may have more use especially when the same professional may need to move from desktop to laptop and may want to bring along eGPU, RAID, maybe Video in devices and maybe the ability to hook up whatever the client tosses in the mix without starting to unhook things to free up ports.

[Craig Seeman]

[andy patterson] “without true PCIE slots “
Perhaps you aren’t aware of what Thunderbolt is.

With Thunderbolt one can move all one’s expansion from desktop to laptop or any other Thunderbolt computer in the facility. Much more cost effecting.

It only get’s better with Thunderbolt 3 which will have the bandwidth to support external GPUs.

I even have the freedom to daisy chain with Thunderbolt. Can’t do that with built in PCIe slots.

Mac run Windows too. Once external GPUs are fully supported, They’ll be that much more freedom especially for those who may want to use FCPX but prefer working in Windows for other software.

[Craig Seeman]

[Lucy Vernall] “I have tried the files that wouldn’t play back on a newer computer and they were fine. Whew!”

Good to hear. Your encodes are fine. I guess it’s time to consider replacing the computer. Keep in mind you can buy a newer used Mac if you don’t have the price for the newest models. You’ll find a BIG advantage with any i7 model made 2011 or later. Intel introduced “QuickSync” which speeds up H.264 encoding tremendously. Current versions of FCPX/Compressor take advantage of this.

One thing to consider is if you’re going to be handing off your encodes for computer playback on old computers like your. If so, you’ll have to modify the settings for playback older computers. You don’t need to do that if you’re posting to typical web services like YouTube or Vimeo but if your file is going to be played directly on the computer, you may have to consider an easier to play back version.

[Craig Seeman]

[Lucy Vernall] “2009 machine, 2.66Ghz Intel Core 2 Duo, 4GB memory”

Those specs could certainly struggle with some clips depending on the settings.

[Lucy Vernall] “Time Machine couldn’t back up, saying ‘an error occurred while copying files’. Could this be related”

Check your hard drive space. Perhaps there’s something else going on with some files on your computer, permissions or corruption related. First thing I’d try is do a Safe Boot and then reboot back to normal. The OS does some maintenance when doing that.

[Lucy Vernall] “export to format ‘computer’ video codec H.264 better quality, resolution 1280 x 720, audio format QuickTime movie (AAC). “

The Profile and Entropy setting could well be a factor on a Core2Duo. if it’s High, CABAC, an older computer could struggle. Main and CAVLC would be easier. Older versions of FCPX/Compressor defaulted to the latter though. You’d have to look at the details of the Preset.

Of course you could test the file on a newer computer and that would let you know whether you computer is the issue vs the actual file.