Canon 70D suddenley stops video recording

Not much info to go one here.

Did it work on the same settings and card before?
Does it record for a period of time then stop?
Is recording on this camera something new to you? Because when you say its stops I kinda am curious as to what you mean by suddenly and if your comparing to another camera?

The camera will stop likely stop at predefined 29min along with most canon dslrs, some have a 4 gig limit, but in addition to that the recording can stop if it hits the buffer max and cant keep up, so if you have the res set high and the card is slow then you may randomly hit the buffer maxing out.

 

I'm not familiar with the SD card brand you have, I only use Sandisk and Lexmark, but using a new card to ensure your card is not going bad suddenly would definitely be worth a small investment, and a backup SD card is always good to have if it doesn't solve the issue.

Otherwise it sounds like your 12 year old camera may have hardware starting to fail after many years of regular use. You can call canon and get their advice, but sending to them for fixing it is likely the cost of replacement if the motherboard is going out.
Also you could try swapping to Firmware, a downgrade to https://hk.canon/en/support/0400270102 1.1.2 (assuming your on 1.1.13 already) and back to the latest could help correct a firmware bugging out, .... but that's more low probability to help suggestion but would be worth a shot.

 

Let us know how it fairs between a new sd or a firmware refresh.

I would note that while the shutter count is alright video runs the camera quite hot and years of heavy video use can take its toll on the sensor.