Video Transcoding -- The Bitrate Factor

By Author: Ivan Cuxeva Jr
Total Articles: 782
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Video transcoding can be a tricky subject you analyze it from the point of view of bit rate however, you will want to know more about a particular subject if you want to encode good-looking videos which may be optimized and shared across different mediums. Simply put bit rate refers to the amount of detail that is stored in a time unit, is reversed to digital media course.

Variable vs. Constant:

If you want to transcode media from one format to another, let's say DVD to AVI, you will need to optimize the encoding settings in order to achieve good results, this is where you are faced with the option of choosing between variable or constant bit rate. Variable bit rate refers to different adjustments which are done to video frames according to the amount of movement that is detected by the codec in a particular scene, this means that if a scene of the media you're trying to encode it has a lot of movement the codec will try to adjust and compensate for these changes by increasing the bit rate in that particular scene or group of frames, if the codec they did not adjust or increase of the bit rate the entire sequence ...
... would look pixelated which would effectively lower the quality of the video file. The very same peak rate manipulation method is used in scenes where there is not much motion, this way the codec is able to lower the bit rate which will reduce the file size and still maintain the quality and low motion frames.

Constant bit rate on the other hand, requires some calculation in order to maintain the quality, this means that if you are encoding a video scene which has a lot of movement and action you should increase the bit rate to preserve the original quality, that is if you're ripping from a high-quality source, the bit rate will need to be adjusted according to the codec that you are using for instance, if you are using DivX you may want to take the bit rate all the way to 1500 kbps in to pass mode, this setting will allow you to get high quality regardless of video movement. If the scene you are trying to transcode doesn't have much movement you can lower the bit rate and still keep a good quality.

Passes:

The amount of passes that you perform while transcoding your video will improve the quality of it, a single pass will allow the codec to gather as much data about the variations of movement in each frame of the media you're trying to encode in order to adjust the bit rate however, a single pass may not achieve impressive results. If you decide to do a two pass transcoding the video quality will improve as the codec has been able to gather as much data as possible and can now adjust the bit rate in a more efficient way. Multiple passes are great for improving the quality of a file but the entire process will take twice as long because obviously the software is performing multiple passes.