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To: Carnac who wrote (44610)	9/9/1999 4:07:00 PM
From: Stoctrash	Read Replies (2) \| Respond to of 50808

...so you're saying that maybe...just maybe,,,, all that R&D spending actually is going somewhere??? Ain't that neat :-) thanks...

To: Carnac who wrote (44610)	9/9/1999 6:05:00 PM
From: John Rieman	Read Replies (1) \| Respond to of 50808

Carnac, you called those hard drive boxes long ago. The only hint before that time was dreams of all in one boxes for consumers(DVD, decoder for DTV/cable/sat/others, WebTV, PC, and audio player). You are all knowing. How long till H.263??????????????????? rs6000.ibm.com Motion estimation estimates the translational motion of objects in the current frame relative to the previous frame. This allows the encoder to reduce the energy in the frame difference by moving pixels around to simulate object motion. The cost is that the encoder must insert a small amount of motion information in the compressed data so that the decoder can reproduce the pixel shuffling exactly. The encoder keeps the quantity of motion parameters low by only estimating the motion for 8x8 or 16x16 blocks of pixels in the input frames. Both MPEG and H.263 enhance prediction and motion estimation by using bidirectionally-predicted (B) frames. One can think of a B-frame as the average of two P-frames that use previous and future input frames as predictors for the current input frame. Generally speaking, a B-frame can be about one third the size of a P-frame. Obviously, the use of B frames implies out-of-order encoding, as the encoder can only encode a B-frame after encoding the requisite previous and future frames. Note that a B-frame never predicts another B-frame; only I- and P-frames are used to predict B-frames. One feature that H.261 and H.263 share that MPEG does not have is support for variable frame rate within a video sequence. This is important in teleconferencing for two reasons. First, the bit rate in a teleconference can be very low, so an encoder must be able to lower the frame rate to maintain reasonable visual quality. Second, the encoder must be able to adjust to sudden changes in video content in real time without warning. For example, at a scene change, the first compressed frame tends to be large; with variable-frame-rate encoding , the encoder can encode the frame and then skip a few input frames before encoding the next frame. In fact, the human eye will not see motion in the video for a while after the scene change. Historically, MPEG-1 was derived from H.261 and JPEG. H.263 is based on H.261 and MPEG-1, and adds some enhancements of its own. On the other hand, MPEG has some enhancements present in neither H.261 nor H.263. All other things being equal, at bit rates of 1 Mbps or above, MPEG-1 video will look better than the same content encoded with either H.261 or H.263. At the common rate of about 1.2 Mbps, with a frame resolution of 352x240 and a frame rate of 30 fps, the visual quality is comparable to or better than that from an analog VCR. In low bit rate teleconferencing (128 kbps and below), H.261 and H.263 video might look better than MPEG video because the first two codecs can vary the frame rate within a video sequence. H.263 can run at lower bit rates than H.261. It can also run at higher bit rates and support larger frames (up to 4 times larger in each dimension). However, if an H.263 encoder does not use the optional modes of H.263, its output should be comparable to that from a similar H.261 encoder.