運(yùn)動(dòng)圖像國(guó)際壓縮標(biāo)準(zhǔn)mpeg-文庫(kù)吧資料
2024-08-14 14:16本頁(yè)面
【正文】 oving pictures and associated audio at up to about Mbit/s ? Part 1 : Systems ? Part 2 : Video ? Part 3 : Audio ? Part 4 : Conformance testing ? Part 5 : Software simulation ? MPEG－ 1視頻壓縮算法必須有與存儲(chǔ)相適應(yīng)的性質(zhì)，即能夠隨機(jī)訪(fǎng)問(wèn)、快進(jìn)／快退、檢索、倒放，同時(shí)需要音像同步、一定的容錯(cuò)能力、延時(shí)控制、可編輯性及靈活的視頻窗口格式，這與多媒體技術(shù)所要求的交互性相適應(yīng)，構(gòu)成了 MPEG－ 1視頻壓縮算法的特點(diǎn)。其任務(wù)是在一種可接受的質(zhì)量下，把視頻和伴音信號(hào)壓縮到速率大約為 流。 Quantization ? ACcoefficients of B and P frames are usually very large values, whereas those of I frames are very small. ? MPEG quantization adjusts itself accordingly. If the data rate increases too much, quantization bees more coarse. If the data rate falls, then quantization is performed with finer granularity. 3 語(yǔ)音編碼 ? MPEG audio coding is patible with the coding of audio data used for Compact Disc Digital Audio (CDDA) and Digital Audio Tape (DAT). ? The most important criterion is the choice of sample rate of or 48kHz (additionally 32kHz) at 16bits per sample value. Each audio signal is pressed to either 64, 96, 128, or 192Kbit/s. ? Three quality levels (layers) are defined with different encoding and decoding plexity. ? An implementation of a higher layer must be able to decode the MPEG audio signals of lower layers ? FFT is applied for audio, and the spectrum is divided into 32 nonoverlapping subbands ? noise level in each subband is determined using a psychoacoustic model. ? In the first and second layers, the appropriately quantized spectral ponents are simply PCMencoded. ? The third layer additionally performs Huffman coding. ? MPEG provides for two types of stereo sound. Two channels are processed pletely independently. In the joint stereo mode, MPEG achieves a higher pression ratio by exploiting redundancies between the two channels ? The minimal value is always 32Kbit/s. ? The layers support different maximal bit rates: layer 1 allows for a maximum of 448Kbit/s layer 2 for 384Kbit/s layer 3 for 320Kbit/s. ? For layers 1 and 2, not all binations of bit rate and mode are allowed, and a decoder is not required to support a variable bit rate. ? In layer 3, a variable bit rate is specified by allowing the bit rate index to be switched. 4 數(shù)據(jù)流 ? An audio stream is prised of frames, which are made up of audio access units, which in turn are divided into slots. ? An audio access unit is the smallest pressed audio sequence that can be pletely decoded independently of all other data. Video Stream ? A video stream is prised of 6 layers: sequence layer the beginning of the sequence layer includes two entries: the constant bit rate of the sequence and the minimum storage capacity required during decoding. A video buffer verifier influences the quantizer and forms a type of control loop. group of pictures layer This layer contains at least an I frame, which must be one of the first images. the difference between decoding order and display order picture layer contains a whole still image. image number. slice layer Each slice consists of macro blocks A slice also includes the scaling used for DCT quantization of all its macro blocks. macro block layer block layer System Definition ? specifies the bination of audio and video data streams ? the coordination of input data streams with output data streams, clock adjustment, and buffer management. ? One could define a protocol to supply the header upon request. ? MPEG does not prescribe pression in realtime. ? MPEG defines the decoding process but not the decoder itself. 5 MPEG1 ? MPEG1的標(biāo)準(zhǔn)號(hào)為 ISO/IEC 11172， 標(biāo)準(zhǔn)名稱(chēng)為 “ 信息技術(shù) —— 用于數(shù)據(jù)速率高達(dá)大約 Mbit/s的數(shù)字存儲(chǔ)媒體的電視圖像和伴音編碼 ” （ Information technology — Coding of moving pictures and associated audio for digital storage media at up to about Mbit/s）。 P幀在最初的兩個(gè) B幀前面?zhèn)魉停诙€(gè) I幀在最后的兩個(gè) B幀前面?zhèn)魉?。?I幀周期性地出現(xiàn)確保差異是相對(duì)于最近的情景進(jìn)行計(jì)算的，能消除錯(cuò)誤的傳播。這種情況涉及那些藏在某些移動(dòng)體后面的物體。 ? 不同的幀類(lèi)型在一個(gè)幀序列中應(yīng)按什么形式排列？ 要保證 I幀必須在任何幀序列中周期性地出現(xiàn)。比如說(shuō)，一個(gè)全新的情景就不能這樣壓縮。 ? 計(jì)算當(dāng)前幀與前一個(gè)幀的差別來(lái)處理那些在視野中移動(dòng)的圖形是非常有效的，因?yàn)槟切﹫D形
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