One of the biggest reasons filmmakers fall in love with the GH4 is its amazing internal high frame rate shooting capabilities. No other DSLR/DSLM can overdrive like the GH4, which offers variable frame rates up to 96 frames per second. This is pretty astounding, and certainly makes the GH4 an incredibly powerful owner – but unfortunately, not all frame rates work like others.
If you want to overdrive your GH4, there are two main ways to do it. The first is the old-fashioned way (as you do with the GH3 or any camera that shoots 60p), which is to shoot at true 60p settings and slow down the 60p video file to 40% (24p) in post. Another option is to use the variable frame rate setting in the menu to shoot anywhere from 2 fps all the way up to 96 fps. If you use this option, the GH4 will actually adjust the clip internally so that your archive plays back in 24p (slow motion) as soon as it finishes recording, just like a RED camera or other high-end cinema camera would. It’s tempting to use VFR mode all the time on the GH4 because there’s a lot of flexibility in the frame rates you can use, and it also saves time in post because you don’t need to slow down the footage. But be aware that the data rate is lower.
When shooting in VFR mode at any frame rate setting, the bitrate is limited to 100mbps. That might sound like a lot, especially since you’re probably used to shooting with a DSLR with a very low bitrate (like 17mbps), but it really isn’t enough when you get to higher frame rates. To put things into perspective, when you shoot 24p at 100 mbps you’re really just spreading 10 mbps of data over 24 frames, whereas when you shoot at 96 fps you’re getting exactly the same amount of data per second , but now you spread it out over 4 times the number of frames, which means you’re getting 4 times less information in each frame. Ultimately, this means the final image quality is much poorer than you might have hoped.
When can 96fps be used
In most cases, I strongly recommend against using 96fps on the GH4 as it won’t deliver great results. These images can appear blocky, thin, and when you color grade, they tend to fall apart quickly. Trying to do any kind of color work on it will make you feel like you’re using an iPhone lens or an old-school video camera, leaving little room to play with in post. Images can also be very grainy and suffer from compression artifacts due to the low bit rate. Still, it can be useful in certain situations—namely, when there’s enough light.
For example, if you shoot in broad daylight at 96 fps, you might be able to get away with it. Since you need to use a 180 degree shutter (meaning your shutter speed is twice the frame rate), when shooting at 96 fps your shutter speed is actually 1/192, considering you are used to shooting at around 1/ Shooting, this speed is very high. This means that if you’re trying to shoot any kind of nighttime exterior (or even most nighttime interiors), you’re going to have a hard time getting the exposure right unless you have a very large lighting kit and know exactly how to use it. However, at noon, this is not a problem because you have such a bright natural light source (the sun) working for you. Ultimately, this allows you to easily get exposures that are bright enough to compensate for your frame rate settings, and you’ll be able to get more usable results… Would I personally shoot at this frame rate? Even in bright sunlight, this rarely happens as the quality is still not as strong as it is at other frame rates. But if I absolutely needed the extra speed of a camera, I would definitely consider it a last-minute option.
60p and 48fps
So, 96fps is clearly not the best choice for VFR mode, but how about some of the other frame rate settings maintaining the 60p gold standard we’re all used to? In my experience, they hold up pretty well – especially when you’re shooting at 48 fps or lower. Shooting anywhere close to 96fps is going to be problematic, once you get down to the 60fps range you’re naturally better off shooting in 60p mode and slowing things down in post (since you can shoot at 200mbps in 60p, While shooting can only be done at 100mbps in the 60fps variant frame rate mode). But once you drop below 60fps, things start to become more useful, especially at 48fps. When you shoot at 48 frames per second, you’re actually slowing down the footage by 50%, which means you halve the 100mbps data rate, ending up with 50mbps – not bad at all. Not too long ago, many of us clamored for a GH2 hack that would let us shoot at 50mbps, as the quality was much better than the stock option on the camera, and in many shooting situations 50mbps would be enough.
So why shoot at 48fps at a lower bitrate when you can shoot at 60p at a higher bitrate? There are many reasons for this, from saving time adjusting footage in post (on a quick turnaround job) to matching frame rates with other cameras (maybe your GH4 is acting as the EPIC’s B camera, shooting at 24 fps). Or in my case, I used it to shoot a music video last week. As many of you know, when you shoot a music video you usually want to increase the speed of the song during playback so that you can super speed the footage in camera and get the slow motion effect in post while the band/singer is standing still Sync to track. This is exactly what I did when I was shooting last week… the speed of the music track was doubled and the frame rate was doubled, which allowed for some nice slow motion shots in camera without going overboard. If we tried to speed up the song further to match my 60p settings, it would be impossible for the orchestra to keep up. So, while I prefer shooting at 60p because I’m always striving for the absolute best image quality, 48fps ended up being a satisfying medium and gave us some great results. Here is one of the screenshots from the shoot, taken at 48 fps:
48fps works really well in this case, and I’m really pleased to see that the images not only look good in camera, but are graded well as well. That said, I still wouldn’t recommend using this setting above 60p unless you’re shooting in a situation where you absolutely need to. 60p will always give you better quality, and the extra few minutes spent slowing down the footage in post are well worth it in my opinion. Not to mention you can get some really nice slo-mo with 60p, since you can slow down the footage to 40%, which isn’t too far off from the 25% you get when shooting at 96fps.
Over the next little while, I’ll be updating this article (or adding a new one) with some screenshots comparing 48fps, 96fps, and 60p, so be sure to check back soon.
