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best bit rate / frame size relationship for h.264 export
Hi there,
I’m fairly new to all this, so please help me out.
I’m exporting time lapse videos from premiere using h.264. The original photos are 2592 by 1728, taken with a Canon 600D. I’m exporting them to sell as stock footage, so I want the export quality to be as high as possible.
My question is, what bit rate should I use?
I also have time lapses made with larger pictures, mostly 5284 by 3486. I’m exporting everything at 30fps.
What bit rate should I use for them?
Is there an easy way I can calculate what bit rate I should use for a given frame size, given that I want the quality to be as good as possible, and I’m not worried about streaming, download times etc? (but of course I don’t want the files to be unnecessarily large.)
I’ve done some searches on the net about this but I haven’t been able to get my answer. Much thanks. -
4 Replies
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L x H x FPS x C / 1024 = Bitrate (kbps)
where:
L = Frame length
H = Frame height
FPS = Frame rate
C = Compression factor (bits/pixel)Blu-rays and DVDs typically have C set to 0.60-0.80. I tend to use 0.40 for very good quality encoding.
For maximum H.264 quality please refer to the following post:
Re: Media Encoder CC – H.264 pixelated result
If you set the bitrate to max, send the job to the AME Queue instead of exporting directly from Premiere Pro.
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Hi Ivan,
Thanks. This is very helpful. So just to be clear, the compression factor is not something that I can set anywhere in the export settings; it’s something I should decide on myself, keeping in mind that .8 is very high and .4 is still really good.
In the equation, is the total LxHxFPSxC divided by 1024? In other words, is it (LxHxFPSxC)/1024 or LxHxFPSx(C/1025)?
One more question: what is the significance of 1.0 compression?
Thanks a lot
Bevis -
[Bevis Lowry] “So just to be clear, the compression factor is not something that I can set anywhere in the export settings; it’s something I should decide on myself, keeping in mind that .8 is very high and .4 is still really good.”
Yes. Note that these values apply to H.264. Higher targets would be more appropriate for other codecs. For example, some stock footage is encoded with ProRes, which is not as compressed as H.264; the compression factor would be closer to 3.0-4.0 bpp.
[Bevis Lowry] “In the equation, is the total LxHxFPSxC divided by 1024? In other words, is it (LxHxFPSxC)/1024 or LxHxFPSx(C/1025)?”
The math works the same either way. It’s just a unit conversion from bits per second to kilobits per second (kbps). You should actually divide by 1024 again (i.e. LxHxFPSxC/1024/1024) to get Mbps, which is the unit of measure Adobe uses. Since these targets are all approximate, you could use 1000 instead of 1024, if desired.
[Bevis Lowry] “what is the significance of 1.0 compression?”
A data rate of 1.0 bpp does not have any absolute relevance. For reference, uncompressed video with full chroma subsampling requires 24 bpp at 8-bits per channel depth. Therefore, a data rate of 1.0 bpp just means the video is compressed by 1/24.
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Great. This is just what I needed.
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