MOVIES

QuickTime
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             Apple’s QuickTime software allows a relatively slow Mac or Windows PC to handle 
               rapidly changing video or sound material in real time. QuickTime allows other 
               applications to play  movies and to perform other QuickTime operations.

What QuickTime Provides
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QuickTime is a system extension — to use it you must put the QuickTime™ file in the Extensions file and restart your computer. Having done this, any QuickTime-aware application, such as SimpleText or MoviePlayer, will be able to play movie files — and more! With QuickTime installed any suitable applications can:-

          •  Play QuickTime movies with any combination of pictures and synchronised 
               sound tracks or MIDI sequences

          •  Play MIDI data in movies to external MIDI devices via a MIDI box, using MIDI 
               Manager (Apple), Open Midi System (Opcode) or FreeMIDI (Mark of the Unicorn) 

          •  Play MIDI data in movies on the Mac itself using the standard MIDI instruments 
               in the QuickTime™ Musical Instruments file  — with CD-quality On a PowerMac

          •  Play Karaoke files

          •  Use compression codecs to reduce the amount or rate of data needed for images 
               — with various compromises in quality

          •  Create preview images in standard file open dialogs

          •  Sample sounds in mono or stereo at any sample rate using 8- or 16-bits per sample 
              with optional compression

          •  Import or export sound files in many formats

          •  Import sound files from a specified portion of an audio CD

          •  Provide hue, saturation, brightness, sharpness, black level and white level controls

          •  Provide sound controls to enable either speaker or to adjust overall volume

          •  Use QuickTime compression or expansion when saving or opening PICT files.

QuickTime accepts video signals to the American NTSC, European PAL or French SECAM television standards at frame rates of 8, 10, 12, 15, 24, 25 and 30 frames per second (frm/s).
It also includes filtering to accommodate material from television (TV) and LaserDisk or from a video cassette recorder (VCR).

ù See the Music chapter for more about MIDI and musical sequences

Playing a Movie in a QuickTime Application
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              When playing a movie file, QuickTime trys to play successive frames at the 
               intended speed (frame rate). If a Mac can’t cope, some data is skipped to maintain 
               timing — this can cause jerky images or sound break-up. QuickTime drops video 
               frames in preference to sound data to minimise the subjective disruption. 

How your Mac performs with such a file depends on its processor speed, drive speed, the nature of the movie (image size, colour depth and frame rate), the presence of a soundtrack and the chosen compression codec.

QuickTime Codecs
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             QuickTime incorporates several different coding/encoding algorithms (codecs), 
              each designed for compressing and expanding different kinds of material to best 
              advantage. At the time of writing the following codecs are used:-

              Animation: uses standard Run Length Encoding (RLE) compression
              Cinepak: for high frame rates where processing time is unimportant
              Component Video: for use with YUV signals
              Graphics: optimal for 8-bit dithered images
              Motion JPEG A
              Motion JPEG B
              None
              Photo-JPEG: baseline set by the International Standards Organisation (ISO)
              Planar RGB
              Video
              Photo CD: decompressor for Kodak Photo-CDs

Apart from Photo-JPEG these are all Apple products. Graphics, Photo-JPEG, Planar RGB and Photo CD are for stationary images — the remainder can be used for movies.

The following notes on codecs may be useful:-

JPEG and Motion JPEG                                                                                           

JPEG compression at the normal quality setting gives good results. Motion JPEGs (or M-JPEGs) use a series of JPEG images to create a full-motion video (FMV) movie — this may require a special card inside your Mac. 

Video and Cinepak                                                                                                 

With these codecs you should select the key frame rate checkbox. Each key frame contains a complete image that’s totally independent of any preceding frames.

The frames between these key frames are created from earlier frames using inter-frame compression — this can reduce size of a movie by half. For a small file simply choose a low key frame rate by entering a large number in the QuickTime Saving Options dialog. A low rate may cause the movie to jump more as you shuffle through it.

Both codecs give better results with a high key frame rate. Files produced with Cinepak are very small, give reasonable quality and colour reproduction and are particularly good for high frame rates — but the compression process takes a very long time! Files created with the Video codec can be very large but are quick to process.

MPEG Movies
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              The Motion Picture Experts Group (MPEG) have devised a universal standard for 
               compressing moving video images. It can provide full-motion video (FMV) from 
               CD-ROM, with a picture quality similar a high-performance video recorder.

FMV would normally need about 22 M of data per second of video. But with the MPEG-1 compression algorithm it’s possible to get good results from a single-speed CD-ROM, even though such as drive is limited to a data transfer rate of only 225 K per second.

Ñ   MPEGs employ complex processes that take up a lot of time and memory!

Ñ   To work with MPEGs you must have a MPEG card — or Apple’s promised new 
          version of  QuickTime and a 100 MHz PowerMac or better (see below).

Ñ   On some computers an MPEG image may be limited to only a quarter of a full screen
          — that’s 352 x 240 pixels.

Ñ   Don’t confuse MPEGs with Motion JPEG (M-JPEG) files. An M-JPEG file requires a 
          data rate of 3.7 Mbit/s compared to 1.5 Mbit/s for an equivalent MPEG.

MPEG Frames                                                                                                        

The MPEG process treats each frame in a similar way to a JPEG, and then compresses the difference between successive frames — this avoids recording too many complete frames. It does this by separating moving foreground objects from the stationary background. Only the motion of foreground objects is then recorded — this is rather more advanced than the simple frame difference compression used by QuickTime.

MPEG movies use three types of frames:-

              I   :  Intra frame, compressed only in relation to the current frame itself 
              P:  compressed relative to the previous frame
              B:  compressed relative to both the previous frame and future frame

in which an Intra frame or I-frame is similar to the key frame used in QuickTime’s Video and Cinepak codecs. An MPEG movie made entirely of I-frames is easily encoded but the compression isn’t ideal. This form of MPEG is used on a PC where it’s known as an XING type MPEG. Such a file is usually slightly smaller than an equivalent M-JPEG file.

The Full MPEG process uses inter-frame compression to produce the smallest possible file. In order to know the contents of future frames the data is stored in a different order to that in which it’s displayed. This process requires the use of a buffer at the viewing end.

Officially, MPEGs should use one of eight frame rates, the lowest at 24 frm/s. In practice, low rates such as 16 or even 12 frm/s are used, although the results can look awful. Files that use these rates have the frame rate inside the file set to an irrelevant value!

Ñ   Some MPEGs movies finish with two identical frames — this is normal!

Ñ   Duplicate frames can appear in material that’s converted from 24 frm/s to 30 frm/s.

Ñ   An MPEG file containing green nonsense or earlier scenes throughout, has probably 
         been downloaded from a remote site in ASCII format rather than binary format. 

Other Features                                                                                                       

MPEG files can also contain sound tracks compressed using psycho-acoustic coding. This can use data rates of 192 kbit/s (comparable to CD quality), 128, 96 or 64 kbit/s. MPEGs can also contain sound samples in the .WAV  format used by Windows. Microsoft’s Video for Windows uses its own .AVI  files.

Working with Video 
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Television Standards
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               Before working with video equipment it’s useful to understand some of the 
                variations in technical standards that exist throughout the world. Although 
                some video recorders accommodate both American NTSC and European PAL or 
                SECAM cassette recordings, these machines aren’t universally used!

Each system uses its own colour-encoding method, horizontal line resolution and frame rate — the latter measured in frames per second (frm/s). The common standards are:-

       z  Cinema Film 24 frm/s
              Standard films are often run at 25 frm/s for transmission in Europe.

       z  PAL 25 frm/s
              The Phase Alternate Line standard is used in the European Broadcasting Union 
              (EBU) and defined by the International Radio Consultative Committee (CCIR). The 
              image has a standard aspect ratio with 625 horizontal lines. Not all of these lines
              form part of the visible image — the remaining lines are switched to black for the 
              interframe blanking period. The French Sequential Colour with Memory (SECAM) 
              system uses the same image size but employs a different colour encoding method. 
              A digitised PAL or SECAM image occupies 768 x 576 pixels. 

       z  NTSC 30 frm/s
              The American National Television System Committee (NTSC) standard for 
              monochrome TV, or colour TV where precise time lock isn’t required. The image 
              has a standard aspect ratio with 525 horizontal lines. Of these, 484 lines (or less) 
              form part of the visible image, whilst the remaining 41 lines switched to black for 
              the interframe blanking period. A digitised NTSC image occupies 640 x 480 pixels.

       z  NTSC 29.97 frm/s Drop Frame
              A variant NTSC for colour TV, sometimes referred to as 30 frm/s even though it 
              isn’t! The first two frames in every minute (but not on the tenth minute) are 
              ‘dropped’ — a total of 108 frames are dropped in every hour.

       z  NTSC 29.97 frm/s Non-Drop
              An alternative version of NTSC in which one hour of ‘video time’ corresponds to 
              one hour plus 3.6 hours of real time. This provides colour pictures without the 
              complication of ‘dropping’ frames.

All broadcasting and domestic video systems use interlaced scanning. In this process each alternate horizontal line is created by alternate frame scans called odd and even frames. For example lines 20 and 22 are produced in one frame and lines 21 and 23 are created in the next. This improves the subjective flicker rate from 25 (or 30) to 50 (or 60) frames per second — much easier on the eyes!

Video Hardware
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             To create and edit movies, or to digitise images from a video input, requires 
              special hardware. PowerMacs often have an inbuilt video tuner, but you may need 
              a video input kit to connect a camera, video cassette recorder (VCR) or other device.

Besides this you’ll certainly need a large (and fast!) disk drive and loads of RAM. To see your work at its best you’ll also need a PAL or NTSC video monitor.

°  Don’t infringe television copyright!

PowerMacs with Built-in Video                                                                                 

Top-flight PowerMacs come with composite and component video inputs and outputs — plus mono and stereo audio inputs and outputs. These machines can handle images of 320 x 240 pixels at 30 frm/s — equivalent to one quarter of a full NTSC screen with the same resolution as a low-resolution VGA monitor. However, this image can be magnified with the hardware zoom feature in the Monitors and Sound control panel — for best matching to the screen try a setting of 256 x 192 pixels.

Video capture requires a hard disk with a speed of at least 10 M per second. The internal fast SCSI drive in a PowerMac is fine, but the external standard SCSI ports aren’t!

Video Capture Cards                                                                                               

               If you haven’t got a PowerMac, or if you need more advanced facilities, you’ll 
                need a video capture card. Older cards may only work at an awfully slow frame 
                rate such as 15 frm/s. For good results you’ll need a rate of 24 to 30 frm/s.

Modern cards can sample full-format video, with an image of 640 x 480 or 768 x 576 pixels at a frame rate of 30 or 25 frm/s for NTSC and PAL respectively. A typical PCI video card has two sets of video and stereo sound inputs and outputs.  Separate cards containing a video tuner are also available. 

For MPEG movies you’ll need to fit a MPEG card into the Digital Audio Video (DAV) slot on an AV Mac’s motherboard. Some AV models come with an Apple Video System card already installed in this slot. Future versions of QuickTime will support MPEGs without a card — but you’ll need a 100 MHz PowerMac or better.

Connections                                                                                                          

AV Macs and some PowerMacs can be connected directly to other video devices, such as cameras and video cassette recorders (VCRs) — and can be used for video conferencing.

In a composite video circuit a single wire (plus screen) carries the picture information — but since the colours are mixed together there’s more chance of picture degradation. Both composite video and audio circuits are usually connected by means of phono (PIN) plugs.

In a component video circuit each element of the signal is sent down a separate wire. The universal S-video system used on Super   -VHS VCRs employs YUV 4:2:2 colour coding and uses 4 way mini-DIN plugs that mate with the 7 way sockets necessary for camera circuits. 

For best results always use the component video connections between the source, usually a camera or VCR, and the Mac’s video input — and between the Mac’s output and the final destination, usually a VCR or video monitor.

The Digitising Process                                                                                             

                For working with movies you’ll need a QuickTime editing application such as  
                 Premiere (Adobe). The Apple Video Player as supplied with some AVs and 
                 PowerMacs is best avoided!

Whilst digitising images you should avoid unnecessary system software — turn off AppleTalk, disable extra extensions and control panels and then restart your Mac. Always defragment the drive prior to a sampling session!

If you’re using component video inputs you should select the Component Video compressor in the Video Settings window of the QuickTime editor. On a PowerMac you should set the monitors to millions of colours and use 16-bit audio sampling at 44.1 kHz — this avoids time-consuming computations for colour and bit rate conversions.

Interlace Problems                                                                                                  

The interlaced form of scanning used in video equipment can cause problems when you connect the non-interlaced video outputs of a computer to another video device — for example, a TV monitor image will jitter up and down at frame rate! This can be overcome by using a computer (such as an AV or PowerMac) or video card that provides a convolved video output. This smoothes adjacent lines to reduce flicker, but with a loss in horizontal resolution. The same problem can occur when feeding video material into a computer device — fortunately most Macintosh software accommodates it!

Video Editing
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               Any Mac with suitable hardware can also control other video equipment for 
                work with video editing. This may involve one or more video recorders, video 
                cassette recorders (VCRs) or a Laser Videodisc. Ideally, the mechanisms of all these 
                devices should be controlled from the Mac via suitable software and hardware.

For editing, the Mac must know the exact point in a recording to make the edit! Some Sony 8 mm camcorders have a Control-L socket that allows the tape to be marked to an accuracy of one second, which is then interpolated to ± 5 video frames. More advanced equipment uses ViSCA (Video System Control Architecture) for ±1 frame accuracy. Such devices may come with a serial port — in other instances you’ll need a V-box to connect to a Mac to a Control-L socket or ViSCA connector.

Broadcast standard equipment usually uses timecode in SMPTE form (recorded on a spare sound track on the video recorder) or as VITC (combined into the video signal) for accurate editing. On most VCR formats the audio Frequency Modulation (FM or AFM) tracks for hi-fi sound can’t be used separately for recording after an initial video recording — preventing you from using them to add extra sounds or SMPTE timecode.

The linear tracks for standard quality sound can be used on their own at any time — although the quality is rather poor and may be unreliable for timecode. Fortunately most Pulse Code Modulation (PCM) tracks for digital sound can also be recorded separately.

ù See the Music chapter for about timecode

Generic Movie Documents
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QuickTime™ Movie (MooV)                                                                                    

             A movie file can be played by any application that supports QuickTime — but
              you must put the QuickTime™ file in the Extensions folder!

Ñ   Some applications add a preview image or a custom icon based on the first image.

Ñ   SimpleText is a perfectly good QuickTime viewer!

Ñ   General-purpose applications such as ClarisWorks let you view QuickTime movies 
          within a document. You can stop the movie and Copy the stationary image.

˝    PCs use a filename extension of .MOV.

Motion Picture Experts Group file (MPEG)                                                                  

            You’ll need to play these files for play full-motion video on CD-ROM. 
             They need a MPEG application and a special card inside your Mac (or the 
             promised new version of QuickTime). 

©Ray White. All Rights Reserved 1997