Super Audio CD is the next generation of audio disc, offering full-range, uncompressed digital multi-channel surround sound. SACD can also be backward compatible using so called hybrid discs with an extra layer that allows them to be played on conventional CD players but then only with ordinary CD quality. SACD can be played on SACD Players, DVD Players with SACD support and if using hybrid discs also CD Players. SACD is currently competing with DVD-Audio as the new audio defacto standard.
The number of times a digital sample is taken, measured in samples per second, or Hertz. The more often samples are taken, the better a digital signal can represent the original analog signal. Sampling theory states that the sampling frequency must be more than twice the signal frequency in order to reproduce the signal without aliasing. DVD PCM audio allows sampling rates of 48 and 96 kHz.
Converting analog information into a digital representation by measuring the value of the analog signal at regular intervals, called samples, and encoding these numerical values in digital form. Sampling is often based on specified quantization levels. Sampling may also be used to adjust for differences between different digital systems.
Scalability offers a set of tools by which video can be coded at different Resolutions (different scales) in one total bitstream.
On the decoder side, video can be decoded at the suitable resolution (scale) extracting a portion of the total bitstream.
It adds compatibility and error concealment.
Types of Scalability
The SNR scalability allows the enhancement of the video quality by means of an enhancement layer bitstream. The DCT coefficients encoded by an another layer are refined between the inverse quantisation and the inverse DCT processes. See also the block layer.
So two different goals are obtained: compatibility, as the base layer bitstream can be decoded by a simpler decoder, and graceful degradation, as the base layer can be better protected in transmission with errors.
The spatial scalability allows the increasing of the picture size. The enhancement layer bitstream refers to the lower layer bitstream in order to get a possible spatial prediction for the macroblock. The spatial prediction is made from the lower layer decoded picture referenced by the lower layer temporal reference, that picture needs to be upsampled to the enhancement layer picture size. In the enhancement layer, prediction can be: only temporal, only spatial or a weighted combination of both. Spatial prediction may be used also in Intra pictures.
The base layer bitstream can be decoded by simpler decoders, while the more complex ones may have larger displays. Error concealment is possible protecting better the lower bitstream during transmission and displaying the upconverted images.
The temporal scalability allows an ehancement of the picture rate. It hasn't been included yet as a tool of a defined Profile.
Frequency (Data Partitioning)
Frequency scalabilty provides an ehancement in terms of "bands" of DCT coefficients. The upper layer would contain those DCT coefficients that have been set to zero in the lower layer stream. It hasn't been included yet as a tool of a defined Profile
Standard Definition Television or SDTV refers to DIGITAL transmissions with 480-line resolution, either interlaced or progressive scanned formats. SDTV offers significant improvement over today's conventional NTSC picture resolution, similar to comparing DVD quality to VHS, primarily because the digital transmission eliminates snow and ghosts, common with the current NTSC analog format. However, SDTV does not come close to HDTV in both visual and audio quality.
Séquential Couleur Avec Mémoire/Sequential Color with Memory. A composite color standard similar to PAL (image format 4:3, 625 lines, 50 Hz and 6 Mhz video bandwidth), but currently used only as a transmission standard in France and a few other countries. Video is produced using the 625/50 PAL standard and is then transcoded to SECAM by the player or transmitter.
A sequence consists of all the pictures that follow a sequence header till a sequence_end_code.
Encoding and displaying parameters are transmitted with the sequence header.
The sequence header can be repeated in order to allow random access, but all the data elements of the repeated sequence header, except those concerning quantisation matrices, must have the same values as in the first sequence header.
The repeated sequence header must precede in the bitstream either an I-picture or a P-picture. In the case that random access is performed to a P-picture, it's possible that the decoded pictures may not be correct.
As the GOP layer is optional the management of the pictures is performed at the sequence layer.
An important item is the fact that the frames are not coded in the order in which they are displayed.
In particular the B_frames, that use references "from the future", are always coded after the P_frame (or the I_frame) used for backward predictions.
The frame reordering causes a delay in the coding and decoding processes. On the coder side the delay is given by the number of B_frames, that must wait for the following P_frame (or I_frame), while the decoder should wait for having full the two frame-memories before starting the display.
For special application is possible to code the sequence without any B_frame with the mode low_delay, set at the sequence layer. In this case the decoder needs only one frame-memory.
In an MPEG file, a sequence header is placed before one or more groups of pictures (GOPs) and contains encoding and displaying parameters. The sequence header can be repeated in order to allow random access, but all the data elements of the repeated sequence header, except those concerning quantisation matrices, must have the same values as in the first sequence header. The repeated sequence header must precede in the bitstream either an I Frame or a P Frame.
To allow for better access and editing, many people place a sequence header after every GOP. In final output, some place fewer sequence headers in (every 5 GOPs, etc.) to save bitrate or make the file smaller.
A slice is a portion of image of 16 lines x ( n x16) pels.
Each slice is coded indipendently from the other slices of the picture.
Therefore the slice layer allows error confinement because, when errors in the bitstream are detected, the decoder can try to continue the decoding process looking for the next slice header.
Video decoding process at the slice layer
Decode all the macroblocks that compose the slice.
Many video editors decode and re-encode your program during the editing
process. Instead of decoding and recoding your entire file when edits
are saved, VideoReDo Plus only recodes a few frames at each cut point.This advanced technique has two major benefits:
Speed: The decoding and re-encoding process adds a great deal of time to your editing session, often hours to create output video. VideoReDo only decodes and re-encodes when it has to, usually just one or two frames at each cut point. This greatly speeds overall performance. VideoReDo output speeds are usually limited by the performance of your disk drives, not your CPU. Although performance will vary from system to system, a good rule-of-thumb is that it takes about 6 minutes for VideoReDo to output an hour's worth of video.
Quality: Each time you decode and re-encode an MPEG2 video stream, you lose some image quality as a by-product of the decoding/encoding process. Successive edits of the same material with other editors can significantly degrade the overall image quality. Since VideoReDo does not re-encode material, there is no loss of quality after repeated edits.
SVCD stands for 'Super VideoCD'. A SVCD is very similiar to a VCD, it has the capacity to hold about 35-60 minutes on 74/80 min CDs of very good quality full-motion MPEG-2 video along with up to 2 stereo audio tracks and also 4 selectable subtitles. A SVCD can be played on many standalone DVD Players and of course on all computers with a DVD-ROM or CD-ROM drive with the help of a software based decoder / player.
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