Showing posts with label videos. Show all posts
Showing posts with label videos. Show all posts
Monday, May 12, 2014
Tuesday, September 10, 2013
Saturday, September 01, 2012
Saturday, July 23, 2011
Wednesday, July 06, 2011
SECAM Video
SECAM, stands for "Sequential Color with Memory". It is an analog color television system first used in France. It is, historically, the first European color television standard.
Just as with the other color standards adopted for broadcast usage over the world, SECAM is a standard which permits existing monochrome television receivers predating its introduction to continue to be operate as monochrome television. Because of this compatibility requirement, color standards added a second signal to the basic monochrome signal, which carries the color information. The color information is called chrominance or C for short, while the black and white information is called the luminance or Y for short. Monochrome television receivers only display the luminance, while color receivers process both signals. Additionally, for compatibility, it is required to use no more bandwidth than the monochrome signal alone; the color signal has to be somehow inserted into the monochrome signal, without disturbing it. This insertion is possible because the spectrum of the monochrome TV signal is not continuous, hence empty space exists which can be utilized. This lack of continuity results from the discrete nature of the signal, which is divided into frames and lines. Analog color systems differ by the way in which empty space is used. In all cases, the color signal is inserted at the end of the spectrum of the monochrome signal.
SECAM differs from the other color systems by the way the R-Y and B-Y signals are carried. First, SECAM uses frequency modulation to encode chrominance information on the sub carrier. Second, instead of transmitting the red and blue information together, it only sends one of them at a time, and uses the information about the other color from the preceding line. It uses a delay line, an analog memory device, for storing one line of color information. This justifies the "Sequential, With Memory" name. Because SECAM transmits only one color at a time, it is free of the color artifacts present in NTSC and PAL resulting from the combined transmission of both signals. This means that the vertical color resolution is halved relative to NTSC. It is however not halved compared to PAL. Although PAL does not eliminate half of vertical color information during encoding, it combines color information from adjacent lines at the decoding stage, in order to compensate for "color sub carrier phase errors" occurring during the transmission of the Amplitude-Modulated color sub carrier. This is normally done using a delay line like in SECAM (the result is called PAL DL or PAL Delay-Line, sometimes interpreted as DeLuxe), but can be accomplished "visually" in cheap TV sets (PAL standard). Because the FM modulation of SECAM's color sub carrier is insensitive to phase (or amplitude) errors, phase errors do not cause loss of color saturation in SECAM, although they do in PAL. In NTSC, such errors cause color shifts.
There are five varieties of SECAM:
· French SECAM (SECAM-L)
· SECAM-B/G
· SECAM D/K
· SECAM-H
· SECAM-K
Unlike PAL or NTSC, analog SECAM television cannot easily be edited in its native analog form. Because it uses frequency modulation, SECAM is not linear with respect to the input image (this is also what protects it against signal distortion), so electrically mixing two (synchronized) SECAM signals does not yield a valid SECAM signal, unlike with analog PAL or NTSC. For this reason, to mix two SECAM signals, they must be demodulated, the demodulated signals mixed, and are remodulated again. Hence, post-production is often done in PAL, or in component formats, with the result encoded or transcoded into SECAM at the point of transmission. Reducing the costs of running television stations is one reason for some countries' recent switchovers to PAL.
Tuesday, May 31, 2011
Thursday, May 19, 2011
NTSC VIDEO
NTSC is short for National Television System Committee. The NTSC is responsible for setting television and video standards in the United States. The NTSC standard for television defines a composite video signal with a refresh rate of 60 half-frames i.e. interlaced per second. Each frame contains 525 lines and can contain 16 million different colors. The NTSC standard is incompatible with most computer video standards, which generally use RGB video signals. However, you can insert special video adapters into your computer that convert NTSC signals into computer video signals and vice versa.
NTSC color encoding is used with the system M television signal, which consists of 29.97 interlaced frames of video per second, or the nearly identical system J in Japan. Each frame consists of a total of 525 scan lines, of which 486 make up the visible raster. The remainder are used for synchronization and vertical retrace. This blanking interval was originally designed to simply blank the receiver's CRT to allow for the simple analog circuits and slow vertical retrace of early TV receivers. However, some of these lines now can contain other data such as closed captioning and vertical interval time code (VITC). In the complete raster, the even-numbered or 'lower" scan lines (Every other line that would be even if counted in the video signal, e.g. {2,4,6,...,524}) are drawn in the first field, and the odd-numbered or "upper" (Every other line that would be odd if counted in the video signal, e.g. {1,3,5,...,525}) are drawn in the second field, to yield a flicker-free image at the field refresh frequency of approximately 59.94 Hertz (actually 60 Hz/1.001). For comparison, 576i systems such as PAL-B/G and SECAM uses 625 lines (576 visible), and so have a higher vertical resolution, but a lower temporal resolution of 25 frames or 50 fields per second.
The actual figure of 525 lines was chosen as a consequence of the limitations of the vacuum-tube-based technologies of the day. In early TV systems, a master voltage-controlled oscillator was run at twice the horizontal line frequency, and this frequency was divided down by the number of lines used (in this case 525) to give the field frequency (60 Hz in this case). This frequency was then compared with the 60 Hz power-line frequency and any discrepancy corrected by adjusting the frequency of the master oscillator. For interlaced scanning, an odd number of lines per frame were required in order to make the vertical retrace distance identical for the odd and even fields, which meant the master oscillator frequency had to be divided down by an odd number. At the time, the only practical method of frequency division was the use of a chain of vacuum tube multi-vibrators, the overall division ratio being the mathematical product of the division ratios of the chain. Since all the factors of an odd number also have to be odd numbers, it follows that all the dividers in the chain also had to divide by odd numbers, and these had to be relatively small due the problems of thermal drift with vacuum tube devices. The closest practical sequence to 500 that meets these criteria was 3 × 5 × 5 × 7 = 525.
Sunday, May 01, 2011
Sunday, April 24, 2011
Interlaced Video
Interlaced video is a technique of doubling the perceived frame rate of a video signal without consuming extra bandwidth. Since the interlaced signal contains the two fields of a video frame shot at two different times, it enhances motion perception to the viewer and reduces flicker by taking advantage of the persistence of vision effect. This results in an effective doubling of time resolution as compared with non-interlaced footage. However, interlaced signals requires a display that is natively capable of showing the individual fields in a sequential order, and only traditional CRT-based TV sets are capable of displaying interlaced signals, due to the electronic scanning and lack of apparent fixed-resolution. Interlaced scan refers to one of two common methods for "painting" a video image on an electronic display screen by scanning or displaying each line or row of pixels. This technique uses two fields to create a frame. One field contains all the odd lines in the image, the other contains all the even lines of the image. A PAL-based television display, for example, scans 50 fields every second i.e. 25 odd and 25 even. The two sets of 25 fields work together to create a full frame every 1/25th of a second, resulting in a display of 25 frames per second, but with a new half frame every 1/50th of a second.
To display interlaced video on progressive scan displays, de-interlacing is applied to the video signal.
One of the most important factors in analog television is signal bandwidth which is measured in megahertz. The greater the bandwidth, the more expensive and complex is the entire production and broadcasting chain which consist of cameras, storage systems such as tape recorders or hard disks, broadcast and reception systems such as terrestrial, cable, and satellite transmitters and receivers, or the Internet, and end-user displays such as televisions or computer monitors. Given a fixed bandwidth instead, interlace can provide a video signal with twice the display refresh rate for a given line count versus progressive scan video at similar frame rate, for instance 1080i at 60 half-frames per second, vs. 1080p at 30 full frames per second. The higher refresh rate improves the portrayal of motion, because objects in motion are captured and their position is updated on the display more often, and when objects are more stationary the human vision combines information from multiple similar half-frames resulting in the same perceived resolution as progressive full frames. This technique is only useful though, if the source material is available in higher refresh rates. Cinema movies are typically recorded at 24fps, and gets no real benefit from common interlacing techniques.
Saturday, April 09, 2011
Electronic Terms ........ 9
PAL - System of video transmission used in Europe and many other countries internationally
Pan and Scan - A procedure where a 4:3 image is taken from a widescreen source by clipping the edges.
Pixels - A Picture Element - the smallest element you can see on a monitor or television display. The more pixels an image contains, the higher its resolution.
Premiere - Video editing software packed created by Adobe Systems.
Progressive - Non-interlace full-frame footage or display device, so-called because a progressive image is displayed in one fast sweep, unlike interlaced images which are displayed in two passes, each pass displaying every other line.
Psychoacoustics - The theory of how the brain interprets audio.
Pulldown - This is the process of making multiple fields from frames in order to change the framerate of a source. Film footage is converted from 24fps to 30fps by creating 3 Fields out of the 2 fields usually contained in a single frame (i.e. 3:2 pulldown). PAL footage uses 2:2 pulldown where 2 fields are kept as 2 fields.
Quicktime - Software developed by Apple for the compression/decompression of video. Contains various codecs including Sorenson and recently Apple's own mpeg4 implementation.
Rainbow Artifacts/Moire - The yellow, purple (and other) coloured artifacts sometimes found on sharp black edges in video footage.
Resolution - The width and height of an image or display in pixels.
RGB - Red Green Blue, a method of storing video data by its red, green and blue components which combined make any colour of light you can see.
Ripping - the process of extracting (usually video) data from a file/format that is dificult to access/alter by normal methods. In particular in reference to the decryption process involved in extracting video data from DVDs. Also used to describe the same extraction process for CD audio and video or audio from games.
Sample Rate - The amount of audio samples every second in an audio stream. CDs are sampled 44100 times a seond.
Saturation - Related to chroma, you can think of saturation as how a colour looks under certain lighting conditions. For instance, a room painted a solid colour will appear different at night than in daylight.
SBC - Smart Bitrate Control, a method of accessing the Fast-motion and Slow-motion aspects of the DivX3.11a codec in order to allow variable bitrate encodes. Pioneered by Nando in his program Nandub.
Scanlines - the horizontal lines that comprise one video frame.
SECAM - System of video transmission used in France, similar to PAL - also plays at 25fps but has a different chroma carriers.
Sorenson - A compression codec available in Quicktime.
Spatial - To do with the 2d space element (i.e. the contents of a single frame) of video. For example, a spatial smoother smooths out blemishes that occur within an area of pixels.
Stereo - Audio that contains two audio channels, a left and a right.
Temporal - To do with the time dimension of video, i.e. the changes of the contents of a video in time. For example, a temporal smoother smooths out blemishes that occur on an individual pixel within a range (period) of frames.
Timecode - The method of interpreting frames in time for use in video editing within given standards (such as NTSC, PAL, Film etc) see also Drop-Frame Timecode.
Video for Windows - The main backbone for video compression codec within windows.
Virtualdub - an open source Windows program for capturing and doing simple editing/compressing of avi files.
VirtualdubAVS - an adpatation of Virtualdub by Belgador to allow easy access to AVIsynth scripts.
Wave - Another term for a (usually) uncompressed audio stream as it can be graphically represented by a waveform.
YUV - A method of storing video information that gives priority (more bits of data) to the luminance of a sample.
Thursday, March 03, 2011
Monday, February 07, 2011
Downloading YouTube Videos
DOWNLOADING VIDEO FROM YOUTUBE
How to download from Video buffering websites like YouTube? We all watch videos on youtube or other such video buffering or video streaming websites. And sometimes you really like some videos and want to have it on your player or on your hard disk so that you can view it later and don’t need to be online for that. So you want to download this video to watch it offline; but I am sure you will already come to know that Youtube does not allow you to download any videos. So how should you do it?
There are some softwares available to do it for you but they are either shareware or have their limitations .But you can do it on your own by copying from the cache folder of the web browser.
Go to: Users->Administrator->AppData(you need to set hidden files to visible to see this)->Local->Google->Chrome->UserData->Default->Cache and there you have it.
Now you need to search it. Leave the files with data as names apart, there would be files like f_randomnos which is what you're looking for, check the 'Date Modified' of the folder and the latest one would probably be your video and then open with VLC player and enjoy the video , you can copy it on your personal folder view it later offline. But don’t use these videos commercially, that is an offense. Enjoy.
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