Pelco IXE manual Rate Control, Profile, GOP Structure

Rate Control

The rate control setting determines the bit rate and quality of each frame in the video stream. There might be a trade-off between image quality and the resources required for video storage when selecting a rate control setting.

CBR: The constant bit rate (CBR) streams video at a fixed number of bits per second. CBR uses the full capacity of the bit rate setting for scenes with or without motion. Video is always streamed at the user bit rate setting.

CVBR: The constrained variable bit rate (CVBR) sets a target bit rate like CBR, but allows the bit rate to drop below the specified value on simple scenes. This rate control still provides predictable maximum storage needs with complex scenes, while using less storage with simple scenes. CVBR is the default rate control setting.

Profile

The profile defines the subset of bit stream features in an H.264 stream, including color reproduction and additional video compression. It is important that the selected profile is compatible with the recording device so that stream can be decoded and viewed.

Baseline: A simple profile with a low compression ratio. A baseline profile is compatible with more recorders but uses more bits to compress quality video than the other profiles. This profile supports I-frames and P-frames. Use the baseline profile in applications with limited scene changes; for example, an indoor scene with a single unchanging primary light source and minimal motion.

Main: An intermediate profile with a medium compression ratio. Main is the default profile setting. This profile is compatible with most recorders and uses fewer bits to compress video than the baseline profile; however, it uses more bits than the high profile.The main profile supports I-frames, P-frames, and B-frames.

High: A complex profile with a high compression ratio. This is the primary profile for high-definition television applications; for example this is the profile adopted for Blu-ray and HD-DVD. The high profile supports I-frames, P-frames, and B-frames.

GOP Structure

The group of pictures (GOP) structure is the sequence in which frames are placed within a video stream. The GOP structure always includes I-frames (intra coded frame) and P-frames (predictive coded frame), but it can also include B-frames (bi-directionally predictive coded frame).

Each GOP structure starts with an I-frame, an image of the complete scene that is used as the reference frame in the structure. P-frames record data changes that are different than the previous frame. This allows the video encoder to save space since the data of the I-frame is not duplicated. B-frames not only capture data changes from the previous frame, but they also capture the data changes from the frame after the B-frame. B-frames are more compressed than P-frames and require more processing power to be decoded.

The camera can be configured to use one of the following GOP structures:

IP: A compression that uses only I-frames and P-frames to provide low latency and a high level of decoder support. This GOP structure is compatible with more recorders and decoders than IBBrBP.

IBBrBP: The most sophisticated H.264 compression available. IBBrBP provides the highest quality image at a given bit rate, but it also increases the latency of the video and requires more processing power for decoders.

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