Topic 4 - Video Data Basic Concepts Video is a collection of bit-mapped still images (called frames) that are taken one after the other. When the file is played these pictures are shown in quick succession to give the impression of a moving image. The number of frames is called the frame rate and this is measured in FPS (Frames per Second). The standard rate is 25 FPS. MM Topic 4 - Video Data

Basic Concepts The size of code used to represent the colour of each pixel in a frame will also affect the file size and picture quality. As with still images this is called the bit-depth or colour depth. Resolution is the number of pixels in the area that has been captured. This is usually measured in megapixels. A higher setting for resolution when a shot is being captured will mean better quality but of course, a higher file size. The bit-rate is the number of bits that are sent in one second when transmitting a video file. If the data cannot be sent quickly enough then the video will not be able to display in real-time. MM Topic 4 - Video Data

4.1 Hardware for video capture 1. Digital video camera 3. Video capture card 2. Web cam 4.1 Hardware for video capture Digital Video camera A digital video camera(camcorder) functions in the same way as a still digital camera. The user points the camcorder at the scene they wish to capture and a lens focuses the image onto an array of CCDs (Charge Coupled Devices) Each CCD corresponds to one pixel in the image being recorded. The CCD is a sensor which changes the light striking it into an electrical signal. More expensive cameras have 3 CCDs for each pixel, one each for red, green and blue. This improves quality. MM Topic 4 - Video Data

1. Digital video camera 3. Video capture card 2. Web cam Digital Video camera This analogue signal is then changed into digital using an analogue to digital converter (ADC). Unlike a digital camera a camcorder must capture a continuous stream of images. Therefore the ADC needs to work much faster in a camcorder than in a camera. Another consequence of capturing a constant image stream is that file sizes are very large - indeed video is the largest of any of the media types (text, images, sounds) you look at in Higher, even after it has been compressed. MM Topic 4 - Video Data

Digital Video camera Digital Signal processor 3. Video capture card 2. Web cam Digital Video camera Digital Signal processor The camcorder has a piece of hardware in it called a DSP(Digital Signal Processor) The DSP automatically alters the contrast and brightness of the video for maximum quality. It also compresses and encodes the data stream into MPEG format before saving it onto a storage medium—disk, memory card or tape. MM Topic 4 - Video Data

1. Digital video camera 3. Video capture card 2. Web cam Webcam Webcams are used for real-time chat, including instant messaging (IM), telephone calls over the internet, live broadcasts and video conferencing. Webcams are a lot less expensive than camcorders because: ● there are fewer CCDs. ● the lower resolution means that the ADC need not be as fast as that fitted on a camcorder. ● they have no backing storage facility MM Topic 4 - Video Data

1. Digital video camera 3. Video capture card 2. Web cam 3. Video Capture Card If a recording was made with an analogue video camcorder then the conversion from analogue and compression will not have taken place. An analogue camcorder can be connected to a device that can be fitted to computers called a video capture card. This receives the video data, converts it to digital and compresses it. A video capture card can also be used to receive data from an analogue video recorder or analogue TV. MM Topic 4 - Video Data

4.2 Storage of video data 1. Uncompressed AVI 2. MPEG 1. Uncompressed AVI AVI stands for Audio Video Interleave and is a standard developed by Microsoft. It is commonly used with Windows Media Player (also developed by Microsoft). AVI is so-called because it mixes in (interleaves) sound and video so that they are stored efficiently, rather than as separate entities where video and audio could be separated and played out of sync. MM Topic 4 - Video Data

1. Uncompressed AVI 2. MPEG 1. Uncompressed AVI AVI is uncompressed but it does have methods of keeping file size compact:   ● frame rate is set at a maximum of 30 fps ● final file size cannot exceed 2 Gb. ● resolution cannot exceed 320 * 240, This makes AVI useful for some files but restricts it to relatively small sections. Microsoft is currently developing a successor to AVI called Windows Media Video which will allow compression. MM Topic 4 - Video Data

1. Uncompressed AVI 2. MPEG 2. MPEG MPEG(Moving Picture Expert Group) is perhaps the most popular standard for video.   It comes in many different versions: MPEG 1, MPEG 2, MPEG 3, MPEG 4 and MPEG 7with most DVDs using MPEG 2. MPEG is a compressed format that uses intraframe and interframe techniques. Sound is stored as a separate ‘layer’ within the file. MM Topic 4 - Video Data

2. MPEG Intraframe compression 1. Uncompressed AVI 2. MPEG Intraframe compression This involves removing data from each frame. MPEG looks for and removes data that either cannot be detected by the human eye or will not affect the overall quality too much. MM Topic 4 - Video Data

2. MPEG Interframe compression This look for savings between frames. 1. Uncompressed AVI 2. MPEG Interframe compression This look for savings between frames. MPEG does not store all the frames but instead it stores certain key frames (i-frames) as jpegs. It then looks for the changes between frames and stores these changes as delta frames. Thus the whole of every frame is not stored—only those areas that might change. If an area of a video clip such as a background does not change over a long period then this does not have to be stored for each frame.  MM Topic 4 - Video Data

4.3 Calculating Video fle size To calculate the size of a video file in bytes you need to know the following: ● The resolution of a single frame ● The colour depth ● The frame rate (no of frames per second) ● The length of the video (time it runs for) MM Topic 4 - Video Data

4.3 Calculating Video fle size Carry out the following steps a. Calculate the number of pixels in a single frame by multiplying height by width b. Calculate the storage needed for a single frame by multiplying the number of pixels by the bit depth. c. Calculate the storage needed for 1 second by multiplying the size of a frame by the frame rate. d. Calculate total file size by multiplying size of 1 second by the length of the clip in seconds. e. Convert the answer into a suitable unit. MM Topic 4 - Video Data

6. Convert into Kilobytes = 921,600,00 / 1024 = 900,000 Kilobytes. Calculate the file size of a one minute uncompressed video clip recorded at 25 fps (frames per second. The resolution was set at 640x480 and each frame is stored in 16 bit colour. 1. Number of pixels = 640 x 480 = 307,200 pixels. 2. Frame size = 307,200 x 16 = 4,915,200 bits. 3. 1 second of clip = 4,915,200 x 25 = 122,800,000 bits. 4. Total file size = 122,800,000 * 60 = 7,372,800,000 bits. 5. Convert into bytes = 7,372,800,00 /8 = 921,600,000 bytes. 6. Convert into Kilobytes = 921,600,00 / 1024 = 900,000 Kilobytes. 7. Convert into Megabytes = 900,000 / 1024 = 878.91 Megabytes. MM Topic 4 - Video Data

Calculate the file size for the following: (Note that the No of colours is given. You have to work out the colour depth. (bit depth) Resolution No of colours fps Time(secs) File Size 640 x 420 16 25 20 64.09 MB 800 x 600 65,536 24 13 285.64 MB 1024 x 768 256 30 12 270 MB MM Topic 4 - Video Data

4.4 Video editing Software Once a video clip has been captured and transferred to a computer it can be viewed and, if desired, edited. To edit video clips you will need to have video editing software such as Adobe Premiere Elements, Pinnacle Studio, ULead Video Studio or Windows Movie Maker. A user would typically be working with several video clips to create a movie. Typical activities would include copying clips, cutting frames from clips, adding or removing audio tracks, adjusting audio volumes, adding titles and credits and inserting transitions and effects. MM Topic 4 - Video Data

Three features which are common to all video editing applications are: 1. Timeline 2. Transition 3. Sequencing MM Topic 4 - Video Data

1. Timeline 3. Sequencing 2. Transition 1. Timeline The timeline area of the screen displays the sequence of video clips in order of viewing. This where you view the various media elements, video, audio, still images, titles in an order and sequence which can then be edited. MM Topic 4 - Video Data

1. Timeline 3. Sequencing 2. Transition 2. Transition Transitions are added between clips and to create an effect when the change is made from one clip to another. Common transitions are wipe (a line wipes across the old image, taking it away as it goes and replacing it with the new picture), fade out (the old image gradually fades to black), dissolve (the old image fades out while the new one fades in without the screen going black), hard cut (the clip suddenly jumps to a completely new image) and peel or page turn (the old image peels away to reveal the next clip). MM Topic 4 - Video Data

1. Timeline 3. Sequencing 2. Transition 3. Sequencing Sequencing simply refers to the order in which video and audio clips are placed. Clips can be easily put into any order and then duplicated, inserted or deleted MM Topic 4 - Video Data

4.5 Graphics card for Video output The final stage of the process is to display the video on screen and a video card is used for this. The DSP (Digital Signal Processor), also called a GPU (Graphics Processing Unit) carries out all of the work needed to display full quality video clips. The DAC (digital to analogue converter) changes the binary information into electrical signals that can be sent to monitors.   MM Topic 4 - Video Data