Both constant bitrate and two press bitrate are the same,right?

[tendra]

To get the same bitrate as original file.

[guns1inger]

Details ? Context ? Software ?

Constant Bitrate means that every frame gets the same amount of data, regardless of need.

2 Pass Variable Bitrate means that the video is compressed around an average bitrate, with some frames getting more and some getting less data, as needed.

Both will give you a target file size.

If the source was encoded with a constant bitrate, then encoding it again with the same bitrate will give you the same file, but may result in reduced quality.

If the source used a variable bitrate then using a variable bitrate again will give you the same file size, but the indivual frames won't be encoded with the same bitrates.

[disturbed1]

Only if you are doing a two pass constant bitrate encode.

Constant bitrate is just that. A constant bitrate across all frames. A two pass encode is used to better distribute bitrate through the video. This allows the encoder to give higher bitrate to more complex scenes, while allocating a lower bitrate to less complex scenes. You end up with a video that has scenes with close to a constant quality.

CBR=Constant bitrate rate variable quality. All scenes receive the same amount of bits regaurdless if they need it or not.
VBR=Variable bitrate rate, almost constant quality. Best used with a min/max/average, especially if encoding for STB compliance, so you don't overshoot the upward bounds of max bitrate decoding.
Fixed Quant=variable bitrate with a constant quality across all scenes.

If quality is most important with little regaurd to size, fixed quant encoding will yield the best results. If size is important, 2 or more pass VBR encoding with an average bitrate targeting the final size is what you want. CBR is just a waste of bits, and really should not be used unless the targeted playback mechanism mandates it (VCD, some streaming protocols, a few hand helds)