I'm copying music from a Kubuntu 24.04 laptop to an Android phone using Dolphin and MTP. Some files copy normally, but others freeze and eventually fail. It seems more frequent with files over 5 MB.
I've tried different cables, USB ports and phones with the same result. I have KDE Connect available, but I'd like to figure out the USB problem rather than just work around it.
A pause in the progress display doesn't always mean the copy has failed. Some data may be buffered before it's written to the phone, so it's worth giving a stalled transfer a little time.
But if Dolphin eventually reports a transfer failure, that's more than a slow progress display. Note the exact error and whether the same files fail repeatedly. That would give you a better starting point for investigating than file size alone.
If you need to get the music across while troubleshooting MTP, try adb push. It uses a different transfer method over USB, so it can also help you check whether the trouble is specific to the MTP route.
You'll need Android platform tools on the laptop and USB debugging enabled on the phone. Authorize the computer when prompted, then use adb push with the source file and destination path.
KDE Connect is a reasonable workaround for now, and LocalSend is another option for local transfers. Neither will explain the Dolphin failure, though, so keep the error details if you want to investigate MTP separately.
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unfiled-before-coffee:
It does eventually say the transfer failed after sitting still for a few minutes. Some files copy fine, then another one fails.