How come my canon t3i flickers while shooting video?

[coolhandluke67]

I noticed that there is a random flicker that occasionally occurs while I film. It did not happen at first. But after around 1-2 hours of shooting I began to notice some flickering. Sometimes it happens a lot, and other times maybe only once or twice, and it seemed to get worse the longer we shot. I posted a link below showing you one of the more extreme examples.
One other thing I would like to mention is that it only happened when we both were in the shot. If only one of us were in the shot it was fine.

Here is a bunch of info. In case you need to know this:
I have incandescent lights. I live in the US so I have AC at 60 Hz if I am not mistaken. I use a 64gb at 70mb per second. I will mention that I do not know the shutter speed at which it was shot. I now have changed it to 1/60. I tried it briefly the next day and it no longer does it. But I am convinced it will after an hour or so.

Has anyone experienced this? Do you guys know what is causing this? Hope you can help. Also fyi I am a beginner so please explain in depth so I understand what you mean lol.

Dropbox - cut version.mp4

 

[KmH]

For shooting video your T3i, and most other DSLRs that can shoot video, uses a rolling shutter.
Your T3i is first a still camera, and a video camera second.

Most video only cameras use a global shutter.

The shutter speed is dependent on the video frame rate, not the shutter speed you can set in the camera.
The shutter speed has to be faster to shoot video at a frame rate of 60 compared to shooting video at a frame rate of 25.

 

[chuasam]

The light flicker. You'd need one of those lovely KinoFlo to avoid flicker.

 

[KmH]

I meant to add that when shooting video using a DSLR camera the shutter curtains do not open and close - because they can't move that fast.
Pro grade DSLRs can shoot only 10 or so frames per second by opening and closing the shutter curtains.
Consumer grade DSLRs, like the T3i, have a much slower shutter burst rate. The T3i's burst rate is a max of 3.7 frames per second, well short of the minimum 25 fps needed for video.

A DSLR turns power to the image sensor on and off to simulate the opening and closing of the shutter curtains.

 

[sniper x]

I have been in the film and video industry for over 35 years. When we made the jump to digital video cameras, that brought an onslaught of drawbacks. One was the storage was too small or slow too take full resolution digital video in the uncompressed realm. Result was looking for a compression algorithm that still retained the quality to a high enough degree, but fit enough footage on the storage medium. What needed to happen was the engineers figured out a way to freeze, and duplicate the non moving areas in the image whilst letting the moving parts of it refresh. As motion went up in the image, the bitrate I creased. As a result, artifacts can and do appear in the image and they can manifest themselves in many ways. What you might be seeing is a combination of the buffer getting hot and compression artifacts in the image due to it and the compression not being able to keep up with the motion. Although there isn't much motion in that image, it still does have twice as much as it did with one person in it. How hot was it I. The room and what frame rate and resolution were you using?