4k video - decent bitrate?

[Patrick Cooper]

I've just exported a time lapse video with Shotcut that was shot with a Panasonic G6. Pixel dimensions are 4096 x 2304. The frame rate is 25fps. I'm fairly new to 4k video and I plan on submitting this clip to some stock agencies. For the bitrate, I selected 100mbps. After exporting, I checked the technical details and the bitrate of the finished file is 75mbps. Just wondering if that's too low for 4k video?

 

If that is considered too low, what would be considered an acceptable range (in terms of bitrate) for 4k video shot around 24 / 25 / 30fps? Bear in mind that I want a balance between good quality 4k video and manageable file size for uploading. Although quality would be good, I don't want to end up with a gigantic file size that's going to take 2 - 3 days to upload (I do have slow upload speeds for my internet by the way.)

 

I did some googling and noted that the Panasonic GH5 can shoot 4k video at 100mbps. So I guess that might be a good target to aim for. With Shotcut, I notice no matter what bitrate I enter, I usually end up with a lower figure. So if I want 100mbps, I might have to input something like 130mbps perhaps.

[Patrick Cooper]

Did another export on got 116 mbps. Hopefully, that should be okay for a 4096 x 2304 video at 25fps.

[Tyler Purcell]

So for reference, 4k Pro Res XQ @ 12 bit 4:4:4 is 1600Mbps. That's a very common camera original for Arri Alexa's. Red Dragon @ 4k 8:1 (highest compression) is 380Mbps per second with Raw capture. The $998 Blackmagic Pocket cameras capture 1080p Pro Res HQ @ 10 bit 4:2:2 at 220Mbps.

 

So when you talk about compression, there are a few things to note. Bit rate is one for sure, but with the GH5, there are a lot of formats to choose from. Normally it captures in 8 bit 4:2:0 Long GOP compression, which is a VERY compressed file format, developed specifically for web deliveries, not for camera originals. Nearly all of the sub $2500 cameras use this low-end codec because it's cheap to buy the licensing and it's "acceptable" quality for youtube and home movies.

 

The GH5 however, with a firmware/software update, should be able to do 10 bit 4:2:2 200Mbps iFrame capture at 4k resolution. The menu's are absolutely the worst on the HG5, none of it makes any sense, so good luck finding that setting, but it exists for sure. Gotta do the update and then flip through the compression settings until you see it. So you SHOULD be ok, as long as your editing software can read the files, which I struggled with as only the newer versions of Adobe Premiere work.

[Robin R Probyn]

4K pro res XQ 1,600 Mbps... really .. . on Alexa.. ?

[Tyler Purcell]

4K pro res XQ 1,600 Mbps... really .. . on Alexa.. ?

Well... that's just the spec @ 4k. I have yet to physically do the math on it. I don't get very many Pro Res XQ shows from the Alexa, most of the people I work with do commercials and music videos and they shoot 422 or 4444.

[Robin R Probyn]

Well... that's just the spec @ 4k. I have yet to physically do the math on it. I don't get very many Pro Res XQ shows from the Alexa, most of the people I work with do commercials and music videos and they shoot 422 or 4444.

 

 

Wow its such a massive file size.. I guess for effects .. but wow massive files.. hate to be doing the down loading !!

Edited August 23, 2018 by Robin R Probyn

[Phil Rhodes]

The other thing to be aware of is that when you ask an encoder for 100Mbps, it's a target. With some formats, such as H.264, the encoder will try to achieve that target by using a particular arrangement of compression settings, compress a frame (or group thereof) and see how close it got to the target. Sometimes it might try again with different settings if it was wildly off. Other codecs (such as ProRes) use fixed settings per frame, so if the frame is simple and it compresses really well, the bitrate will drop.

 

In neither case will the file usually hit the specific bitrate with any degree of precision. Some rate control algorithms are better than others.