That type of USB flash is one of the cheapest kinds of storage and least reliable.

They’re good for a quick copy between computers, but not for reliable storage or backup.

There won’t be any damage. Worst case, the video files might get deleted.

SD cards are considered one of the least reliable forms of data storage. They wear out quickly compared to things like SSDs or hard drives.

There can be differences between different SD card brands and manufacturers. Sometimes things labeled “high endurance” can be just a firmware difference in the same physical device. Although, that may offer some improvement.

Overall, most quality SD cards from reputable brands (not the cheapest) work okay. If you’re worried about losing footage, connecting the camera to a local NVR (computer that saves video recordings) is the next step up in reliability.

Samsung easily has the best and most reliable consumer SSDs. Their manufacturing, firmware, and history for SSDs is very good.

No such thing as long term SSD storage.

All SSDs leak elections. Putting more bits in a cell can potentially make it easier to lose data, but that’s why we use RAID to check, and backups if things go wrong. Realistically, by the time your SSD starts failing, you can buy a new replacement that’s cheaper. High density is where all the manufacturing savings are. It doesn’t make a lot of sense to spend more for SLC when you can get faster, larger, cheaper SSDs and replace as needed.

Actually U.S. courts make a distinction between “streaming” which is temporary and require a connection for every repeat viewing and “downloading” which stores more permanent version that can be watched without an internet connection.

The YouTube ToS allow you to stream videos. They restrict downloads. If you break that, your “cached stream” isn’t legal to begin with. It’s like going into a store giving free samples and taking a box full. You have to follow their rules, or the legal system may rule against you.

Not that it realistically matters for personal local copies. Who knows, there can be a possible fair use exemptions in certain cases.

The TrueNAS gods say to leave HDDs plugged in and spinning.

The current way to store digital data is as “living data” with backups. Data only exists if it’s constantly verified to exist. You can’t verify an unplugged HDD. Of course, you need a 3-2-1 backup system, and have to continually verify those backups as part of the living system.

The magnetic platters in a HDD are actually decently reliable. Sure a cosmic ray or error may flip a bit, but that’s why we have backups and redundancy elsewhere in the system. That flipped bit won’t actually damage the hardware.

The real concern with HDDs is that they mechanically wear out and break. They stop spinning. The motors malfunction, the lubricants dry up, the metal bearings wear down, etc.

TrueNAS says the most dangerous time in a HDDs life is when it is spinning up or slowing down from a stop. This gives the most mechanical stress on the HDD. They says it’s better to leave them powered and spinning 24/7 than to unplug them or despin them.

H.264 and x264 are the same thing. H.264 is the name of the math standard. x264 is the name of an open source software that implemented that math.