coming up with high/avg/low

[jkavalon]

hey i never could figure out how to come up with the high/avg/low bitrate values for vbr in cce. i know what size why video has to be, just don't know how to calculate those numbers... can anyone help me out?

[bobwillis]

I'll attempt to help :)

The min value is the lowest bitrate that will be used in simple scenes (easy to encode scenes). If this figure is too high, then bits will be wasted. Most people use a value of 0 to 1000 (I use 0).

The max value can be limited by what media you are going to put the MPEG2 file on. If it is a DVD, then the maximum for video+audio is approximately 9800kbps. If you have just one AC3 audio track then a conservative maximum is 9350kbps. I subtract another 450k for each additional AC3 (6ch) audio track. All my encodes usually one have one AC3 (6channel) track, so I use 9350kbps.

The average bitrate is crucial in determining the final file size of your encode.

Here is an example of calculating average bitrate: If your video is 2 hours long and you don't want the video file size to exceed 4.37GB then the average bitrate can be calculated as follows.

4.37GB = 3.754 * 10 ^ 10 bits.
(note to convert GB to bytes, multiply by 1024*1024*1024)
(to convert bytes to bits, multiply by 8)

Avg bitrate = (size in bits) / (time in seconds)
= 3.754 * 10^10 / 7200
= 5.214 * 10^6 bits/sec
= 5091kbps

Remember that audio + video cannot exceed your target size, so if you are encoding each separately, then it is necessary to calculate each separately.

I appreciate this is complicated and mathematical, perhaps someone can put it in a simpler fashion.

Here are some useful rules of thumb:
1GB = 1024*1024*1024 bytes
1byte = 8 bits
1kbps = 1024 bits/sec
1Mbps = 1024 kbps

No doubt somebody will have a right laugh at me for posting this :)
I hope it helps.

Regards,
Bob

[jkavalon]

yea i feel stupid for not being able to figure it out, but thanks man you helped a lot.