Forum Archive Home -> Video Conversion -> Both constant bitrate and two press bitrate are the same,right?
Both constant bitrate and two press bitrate are the same,right? |
| tendra posted 2009 Nov 01 04:11 |
| To get the same bitrate as original file. |
| guns1inger posted 2009 Nov 01 04:31 |
| 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 posted 2009 Nov 01 04:35 |
| 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) |
Login/Register to our forum to be able to post here.