多媒体知识点答案——部分.doc

1. Explain the meaning of FOURCC tags in AVI container “00db”, “01dc”, “01wb”, “vids”, “auds”, etc. 2. What is audio CD data rate? 44.1 kHz * 16 *2 = 1.4112 Mb/s3. What are audio coding goals? Fidelity: Maximize the perceived audio quality at the audio decoder (minimize the distortion). Data rate: Minimize the amount of digital data to represent the original audio signal. Complexity: Minimize the computational complexity. Delay: Minimize the coding delay.4. Explain the structure of Waveformat Chunk Typedef struct ID chunkID; long chunkSize; short wFormatTag; unsigned short wChannels; unsigned long dwSamplesPerSec; unsigned long dwAvgBytesPerSec; unsigned short wBlockAlign; unsigned short wBitsPerSample; unsigned short cbSize*; FormatChunk;5. Describe potential coding errors in audio coding. Sampling errorsAliasing effect; Quantization errors: Overload errors Round-off errors Storage and transmission errors;6. Explain the difference between lossy compression and lossless compression. 所谓有损压缩是利用了人类对图像或声波中的某些频率成分不敏感的特性，允许压缩过程中损失一定的信息；无损压缩是利用统计冗余进行编码压缩，可完全恢复原始数据而不引起任何失真。7. Describe the difference between uniform quantization and non-uniform quantization. 把输入信号的取值域等间隔分割的量化称为均匀量化。非均匀量化是一种在输入信号的动态范围内量化间隔不相等的量化。8. Describe the Bitmap Structure public class BitmapInfoHeader public int biSize; public int biWidth; public int biHeight; public short biPlanes; public short biBitCount; public int biCompression; public int biSizeImage; public int biXPelsPerMeter; public int biYPelsPerMeter; public int biClrUsed; public int biClrImportant; 9.What is the definition of entropy?信源的平均不确定度。10. Describe the procedure of Huffman coding.Huffman树的构建；11. Describe ADPCM coding process and the full name of ADPCM in EnglishADPCM ：Adaptive Differential Pulse Code Modulation12. What is 010 editor? How to define struct and array?13. Describe the difference among Fourier transform, Fourier series, Discrete time Fourier transform and Discrete Fourier transform.傅里叶变换在时域和频域上都是连续的；傅里叶级数时域有限，频域上是离散；离散时间傅里叶变换时域上离散的，频域上是周期或离散的；离散傅里叶变换在时域和频域上都是离散的。14. What is the computation complexity of decimation in time FFT?N*LogN。15. What is the purpose of windowing before time to frequency mapping?使得无限时长的信号截取为有限长的信号，便于计算机处理。16. What are four types of redundancy in image and video coding?17. In image and video compression why do we prefer using YUV color space rather than RGB space?应用了视觉冗余，这样便可以对色度分量使用更少的采样点。18. What is sampling resolution for CIF?抽样分辨率。19. What are three basic types of coded frame in video coding?I，P，B20. Explain motion estimation and compensation将活动图像分成若干块或宏块,并搜索出每个宏块在邻近帧图像中的位置,计算出两者之间的空间位置的相对偏移量,那么得到的相对偏移量就是通常所指的运动矢量,而得到运动矢量的过程称为运动估计. 当运动矢量为分数像素精度的时候，预测块并不真实存在，需要通过内插的方式得到。因此得到了运动矢量并不等于就得到了预测块。所以运动补偿就是利用运动矢量得到预测块的过程。21. What is PSNR?峰值信噪比。22. What is the purpose of DCT?减少数据相关性，便于后续熵编码和其他处理。23. Why is zigzag scan applied before entropy coding in JPEG?使得更多的零系数放在一起，便于熵编码。24. How to address the issue of bit error transmission for JPEG compressed bit streams?插入同步字节。25. Why do we apply differential coding to DC coefficients in the process of JPEG compression?DC系数变化比较小，因此使用差分编码。26. What is the difference between an MCU and a data unit? Describe their relationship.Minimum Coded Unit,27. Describe four modes of operation employed in JPEG compression.based, progressive DCT-based, lossless, and hierarchical. 28. In JPEG AC entropy coding, what does run length mean? What is the maximum value of run? What does size mean? What does a (0, 0) run size pair mean? 0系数的长度；非零系数的最大值；非零系数的最大值需要用多少位来表示；（EOB）（0，0）代表结束29. What is the difference between VLC and VLI in JPEG coding? VLCs and VLIs are codes with variable lengths, but VLIs are not Huffman codes.VLC 和VLI均是变长码，但是VLI不是Huffman码，它的编码分为两部分，前半部分为该符号所占位数，后半部分才是实际值。30. What are markers used for in JIF? SOI, EOI , SOF, SOS31. Describe the full name of SOI, EOI , SOF, SOS.32. What is JPEG file interchange format used for? 用于JPEG标准的数据存储。33. Describe JPEG encoding and decoding procedure respectively. 34. Describe the applications of H.261, H.263, MPEG-2H.261 视频会议，H.263 视频电话， MPEG-2 DVD35. Describe video encoding and decoding procedure.H.261使用了混合编码框架，包括了基于运动补偿的帧间预测，基于离散余弦变换的空域变换编码，量化，zig-zag扫描和熵编码。36. What is GOP? What is a video sequence? What is a slice?Group Of Picture，序列包含多个GOP，多个slice组成一个GOP。37. What is H.264 MV resolution? Motion Vector 分辨率1/4 Pixel38. Does H.261 allow B frame?No39. Which video coding method uses 4x4 DCT transform? H.264 wmv940. Is the video data stored in coding order or display order? Coding order41. Does video coding standard specify encoding process or specific decoder implementation? No42. Which of the following is true? Aa) Every slice shall contain at least one macroblock. b) Slices can overlap. c) The position of slices mustnt change from picture to picture. 43. What is the difference between H.264 main profile and baseline profile? Baseline profile 需要的计算能力低，占用系统内存少，适合于实时视频编码 main profile 提供高质量低码率视频44. Describe three possible NAL unit types. VCL NAL-unit及non-VCL NAL-unit Parameter Sets与Supplemental Enhancement Information (SEI)45. In H.264 coding what types of macroblock can be an I or P slice contain? I slice contain intra-coding block; P slice contain intra-coding and inter-coding.46. Which of the following is true? Ba) A Baseline Profile coded picture may contain a mixture of I, P and B slices; b) A Main or Extended Profile picture may contain a mixture of I, P and B slices. 47. What types of data does a slice contain? How about MB data? MB_type etc.48. How is the motion vector transmitted in H.264?通过预测进行传输，传输差值49. In H.264 encoding, Intra 4x4 frame prediction is suited for 1)1) Coding of parts of a picture with significant detail. 2) Coding very smooth area of a picture. 50. How is DCT implemented in H.264? What about quantization? 整数型的矩阵变换 H.264 uses a scalar quantizer 标量量化51. In Baseline Profile, what entropy coding methods are employed? VLC-based entropy coding52. How many audio samples does an MP3 frame contain? 115253. Why are scale factors used in MP3 quantization? 调整编码速率54. In MP3 coding, the ordered frequency lines are divided into three distinct regions. What are these regions? 全0， count1，非055. In TNLS of MP3 coding, what are the outer and inner loops used for? What is global_gain used for?Outer loops amplified sfb innner loop nonuniform quantization huffman coding The global_gain, defines the quantization step size used for onechannel within a granule56. What is the purpose of using bit reservoir in MP3 coding? 标识mp3规格57. How do you know whether an MP3 stream is MPEG 1 lay