No difference 50M vs 25M vs 16M bitrates

Started 11 months ago | Questions
Frank_GH New Member • Posts: 23
No difference 50M vs 25M vs 16M bitrates

Hi,

Do you see any difference in image quality when bitrate is as low as 16 Mbps? I have a sony a7iii and three bitrates are available in full HD : 50M, 25M and 16M.

I tested these 3 bitrates and found no difference in image quality, even after editing the videos in Final cut pro. I was told higher bitrate is better, especially when you plan on editing videos. I wonder why I can't tell the difference. Am I missing something?

Details on what I did :
The 3 videos were Full HD (1080p). They were imported in Final Cut Pro and exported as a "master file" (using H.264) without any "real" editing. I did several rounds of importing-exporting, in an attempt to lose file size and quality. Then I watched them on a 1080p screen. My eyes noticed no loss of quality. File size decreased a little when exporting the first time, but stayed the same on subsequent rounds of exporting.

Thanks in advance!

ANSWER:
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darg Contributing Member • Posts: 504
Re: No difference 50M vs 25M vs 16M bitrates
1

The HD bit rate is only 4.5Mbits for the video signal so over sampling to such extremes as 4x or more isnt really showing much improvement since there isn't a lot to begin with.

Only reason to go to higher rates would to get a little bit smoother panning action and fast cuts but that's it. Not much more to win.

You would get more quality out of these when you have a camera with different compression ratios. I'm no longer in video but I think most cams have 4:2:0 ratios nowadays. An increase to 4:4:2 or even 4:4:4 would help more and increase bit rate only marginal.

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pannumon Veteran Member • Posts: 3,118
Re: No difference 50M vs 25M vs 16M bitrates
2

If you are shooting a static subject with no fine detail, the smaller bit rate is probably enough to capture all the information, and there is no visible difference between the bit rates.

Bit rate setting typically specifies the upper limit for the actual bit rate. In case of static subject, the actual bit rate can be than the maximum bit rate. Try shooting for example foliage when there is some wind. You should start seeing differences in the image quality and probably also in the file size.

You can check the actual data rate in Windows by selecting properties from the file, and then details tab. Alternatively, you  calculate the actual average bit rate (in Mbit/s) of your video files by dividing the file size (in bytes) by the video length (in seconds) then multiplying it by 8 (convert bytes to bits) and dividing by a million (convert bit/s to Mbit/s). Note that the files also have audio, which very slightly adds to the bit rate (typically less than 0.2Mbit/s).

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OP Frank_GH New Member • Posts: 23
Re: No difference 50M vs 25M vs 16M bitrates

Thanks to both of you!

Frank

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