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Is it possible to set a specific bitrate?

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Alessandro Strickner
Is it possible to set a specific bitrate?
on Oct 15, 2015 at 1:20:50 pm

Hi everybody,
I am helping some friends doing a small reel for a contest, using After Effects.
I am not a motion/video designer professional, I am more a 2D Graphic Designer, so I'm having some problems matching the contest's requirements.

They ask for:
MPEG4 – File
H264/MPEG–4 AVC,
Bit Rate 1024 Kbit/sec,
25 Frame/Sec
640x360 pixel PAL
file .MP4

I managed to set everything right, except for that "Bit Rate 1024 Kbit/sec,".
I exported a quicktime .mov from AE, and imported it into Adobe Media Encoder.
On the bitrate settings, it seems like I can't just write "1024kbps" (that I suppose it's 1Mb) but I only can set a "maximum limit" of 1Mb.
The result, as a matter of fact, has a bitrate of 988.

Since, as I said, I'm not a professional video designer, I actually don't know if that 1024 requirement is meant as "a MAX bitrate of 1024", meaning my 988 is fine.

Am I wrong?
If positive, how do I set a specific bitrate if it's even possible?

Many thanks in advance.

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Ryan Holmes
Re: Is it possible to set a specific bitrate?
on Oct 15, 2015 at 5:10:11 pm

Their 1024kbps is likely a combined audio+video data rate. So whatever you set your audio to (128K, 160K, 192K, etc) you'll need to subtract that amount from your video data rate. Given these specs make sure that you're doing a CBR (constant bit rate) encode. Otherwise, you'll be on a VBR (variable bit rate) encode and the data rate will fluctuate depending on the motion contained in the video.

Now with a VBR you can set a ceiling and the encoder won't go over that ceiling. If overall file size is a concern then VBR is a good option (2-pass VBR specifically), but your encode will likely take longer. If overall file size isn't a concern then CBR is probably the best option.

Ryan Holmes

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