비디오 압축 알고리즘은 Inter-frame과 Intra-frame의 두가지 주요 카데고리로 구분됩니다. Intra-frame압축의 경우, 각자의 전달된 비디오 이미지 또는 샘플들은 각기 독립적으로 압축이 됩니다. 이에 반해, Inter-frame압축의 경우, 근접 프레임들간의 차이점만을 압축합니다. 일반적으로, Inter-frame 알고리즘은 Intra-frame알고리즘 보다 더 높은 압축율을 제공합니다. Inter-frame 압축의 압축율을 높이게 되면 속도가 떨어지며, 반대로 그 압축율을 낮게 하면 속도는 개선됩니다. Inter-frame 압축은 통상 실시간으로 비디오를 압축할 수 없으나, Intra-frame 압축은 실시간 압축이 가능합니다.
I-FRAME(Intra-Frame)는 정지 영상을 압축하는 것과 동일한 방법을 사요하는 것으로 연속되는 화면의 기준을 이루는 화면.
P-FRAME(Predict-Frame)는 이전에 재생된 영상을 기준으로 삼아 기준영상(I-FRAME)과의 차이점만을 보충하여 재생하는 화면이며 그 다음에 재생될 P-영상의 기준이 되기도 한다.
B-FRAME(Bidirectional-Frame)는 I-영상과 P-영상 또는 P영상과 다음 P-영상 사이에 들어가는 재생된 영상인데 두 개의 기준 영상을 양방향에서 예측해서 붙여내는 영상이다.
위 사이트에서 자료를 찾아보면은 성능 용구 사양에 따른 올바른 코덱을 빠르게 선택하기 위한 자료를 제공해주는데, 비디오 크기가 320x240일 때, frames/sec이 10.5이라는 값을 제시하였다. 320x240이면 CIF사이즈 352x288과 흡사한 크기인데.. QCIF사이즈(176x144)이면 얼마정도 해야하는건가?? 흠흠..
The Agora Labs elemedia H.263 Codec was originally developed at Lucent’s Bell Labs. There are three versions of H.263 (or H.261 v1), H.263+ (or H.263 v2) and H.263++ (or H.263 v3), this codec implements the baseline version. H.263 baseline version (H.263 v1 with no options enabled) is compatible with MPEG-4 "short header".
The H.263 codec has many options that can be negotiated each time a video call is made, these options can be changed while the codec is running.
H.263 and H.263+ are not compatible codecs. While H.263+ can decode an H.263 encoded stream, there is no requirement for H.263 to decode a stream encoded in H.263+. H.263+ and H.263++ are compatible, provided that the extra capabilities H.263++ adds are negotiated to be not used.
H.263 specifies several video frame sizes - SQCIF (96x144), QCIF (176x144), CIF (352x288), 4CIF (704x576) and 16CIF (1408x1152). At least one of SQCIF and QCIF must be supported, the other sizes are optional. The Agora elemedia H.263 codec SDK supports all these frame sizes, and supports non-standard frame sizes by centering the picture within a larger frame.
The H.263 softcodec was designed to run on IP based networks, and is more resilient to packet loss than H.261. H.263 can run on IP networks, and the Agora elemedia H.263v1 codec can output packets that conform to RFC 2190, "RTP Payload Format for H.263 Video Streams." Agora's RTP stack also supports RFC-2190. If you use both Agora's H.263 codec library and Agora's RTP/RTCP stack, your integration task becomes easier.
Like H.261, the H.263 specifications define how to decode the video stream, the H.263 encoder is left up to the developer's discretion. Agora has made many improvements to the encoder in order to improve the viewer's experience of the picture. One example is that Agora will perceptually encode the video frames so that the most important pixels get the highest priority over the data stream. This is especially important when using the H.263 codec over an analog phone line with a v.32 modem, or when using the H.263 codec on a mobile phone which has a limited bandwidth.
H.263 and other videoconferencing encoders and decoders are designed to operate in real-time on available, inexpensive processors because a video telephone call or video conference can tolerate only a very slight delay. Other video encoders do not run in real-time and do not need inexpensive processors because they are used to encode data to a disk or tape and only the decoder needs to run in real time.
A mode of H.263 is compatible with a mode of MPEG-4, and the two codecs use some of the same patents. MPEG-4 has a group, the MPEG-LA that will license the use of the MPEG codec. Its not clear that they collect royalties on H.263, they have stated in a telephone conversation that an MPEG-4 license covers H.263, but wouldn't say if that license was needed. Thier website makes only a couple of mentions of H.263 at this time, once in a list of patents, and once in a news release that says "In addition, a video plane with short header MPEG-4 Visual Simple profile signal is compliant with the H.263 baseline standard." However, the MPEG-LA (does LA mean "licensing authority" or "lawyer's association?) does not license the rights to Lucent's patents. And Lucent has sued Microsoft and other companies because of patent violations.
Agora Labs provides indemnity from Lucent patents with its H.263 codec.
Agora Labs is a premier H.263 codec IP stack module supplier, providing a video codec that has a small footprint and is fast. Agora prides themselves on their support which is unparalleled. Please contact us for more details.
The elemedia H.263 SDK is available as a binary module for use by system developers. It has been used in many systems, including Windows servers and workstations, and Linux servers and workstations. An H.263 .DLL is available off-the-shelf.
