TechCon 2014 Atlanta, GA

Transcription

1 Slide 1 Mastering The Video Signal Bruce D. Balmer, MBA, CIRM, CLVS, CCVS, CME Slide 2 The Video Signal Standard Class New to motion video Advanced Class Exposure to motion video Less technical No assumptions More technical More not in book material Stays closer to the book in level and depth of presentation More Random Thoughts Will require some self-study Slide 3 Overview Video Signal Elements YUV YP BP R Sync The Digital Image Fields Frames GOP Media Formats Analog Digital Optical Disc Solid State Acquisition Making sense of digital file naming strategies Best practices for digital legal video acquisition 1 P age

2 Slide 4 The Video Signal Video Signal Elements Slide 5 Video Signal Elements Color is defined by three different measurements: Chrominance: the amount of color information in the picture Luminance: the amount of white light mixed in with the color Hue the wavelength of the color Red has a long wavelength Green has a medium wavelength Blue has the shortest wavelength Saturation: the intensity of color, or how much light is mixed in with the color Lavender versus purple P. 60 Slide 6 Video Signal Elements The analog video signal is a combination, in some manner, of color, brightness, saturation, and synchronization pulses Luminance (Y) Measurement of the eye s perception of the intensity of the light Luma video signal component that carries the monochrome portion of the image that determines image brightness Chrominance (UV) U represents the blue component less the luma signal V represents the red component less the luma signal YUV; Y P BP R; Y, R-Y, B-Y all are representations of an analog video signal The highest quality analog signal for standard definition video is Y P B P R P P age

3 Slide 7 Video Signal Elements The analog video signal is a combination, in some manner, of color, brightness, saturation, and synchronization pulses Line Sync Pulse (H / V) Single short pulse, indicates start of every line Frame Sync Pulse Series of longer pulses, indicate start of every frame Color Sync Pulse P. 60 Slide 8 Video Signal Elements Composite Video Combines luminance and color signals, along with line and frame sync pulses on one stream Typically the lowest quality analog source Usually indicated as a yellow RCA jack or BNC connector Often positioned with red/white RCA jacks that carry unbalanced audio signals P. 60 Slide 9 Video Signal Elements S-Video Signal Splits luminance and chrominance signals onto two separate signals Y/C Typically a higher quality source than composite (more lines = more resolution) Typically indicated as a four-pin connector (with two grounds) Essentially obsolete; very few cameras include S-Video ports (Panasonic AG-HMC80) P P age

4 Slide 10 Video Signal Elements Component Signal Can be analog or digital, depending on type Splits video signals into three steams Typically a higher quality source Analog RGB signal converted into YP B P R Y -luma P B - Difference between blue and luma (B-Y) P R - Difference between red and luma (B-Y) Green/Blue/Red RCA cables or BNC P. 60 Slide 11 Video Signal Elements Component Signal - Digital Analog video converted via image sensor(s) into digital data according to a specific coding sequence based on binary mathematics Data is coded as pure red, green, and blue channels, along with luminance Usually labeled as YC B C R (3 wire) or RGBY (4 wire) p. 62 Slide 12 Image Sensors CCD : Charge-Coupled Device CMOS: Complementary Metal Oxide Semiconductor Less expensive to produce Suffer from Rolling Shutter Very much a model by model issue 3-chip camera systems provide superior optical performance to small single chip system Large single chip systems (DSLR) provide different capabilities (depth of field) Not quite as useful in Legal Video Audio and operating temperatures potential issues Reminder from previous class, p. 6 4 P age

5 Slide 13 Overview Video Signal Elements YUV YP BP R Sync The Digital Image Fields Frames GOP Media Formats Analog Digital Optical Disc Solid State Acquisition Making sense of digital file naming strategies Best practices for digital legal video acquisition Slide 14 The Digital Image Fields, Frames, and GOPs Slide 15 Frame, Frame Rate, and Field A frame contains all the information necessary to create an image The frame rate is the number of frames displayed per second, designated fps, and basically allow the system to present a smooth image A field is created when a frame is split into two parts, with one part containing odd horizontal scan lines and the other containing even horizontal scan lines p. 24 / 67 5 P age

6 Slide 16 Interlaced Scanning Interlaced scanning video combines two successive fields of video odd line field + 1/60 sec + even line field = frame (@ 30 fps) First developed in the 1930s as a way of improving image quality on CRT monitors Only CRT displays and certain plasma displays actually display interlaced video, making it basically obsolete today Most DVD recorders make interlaced video Interlaced favors rapid motion (to a point) At 12 fps (frames per second) we perceive a series of images as a moving picture. This is called persistence of vision. At 30 fps we exceed the threshold of retention and see only a smooth picture and not the transition between frames p. 24 / 67 Slide 17 Interlaced Fields Slide 18 Progressive Scanning Progressive scanning displays one frame of video captured at one unique time. All lines of a frame are drawn in sequence Progressive requires twice the bandwidth of interlaced video (720p 1080i) LCD computer monitors, HD TVs, and webenabled devices (ipad) are all progressive display devices Progressively scanned images have about 50% greater apparent clarity of detail than equivalent interlaced images. p P age

7 Slide 19 Progressively Segmented Frames Progressive images bandwidth requirements can be reduced by scanning every other line as well The fields are scanned at the same instance in time rather than at different points in time. Allows for less bandwidth while preserving quality Designated as PsF p. 67 Slide 20 Group of Pictures Groups of Pictures (or GOP) are a successive series of frames grouped together An encoding/ decoding program can be used to analyze what changes and doesn t change within frames of the GOP Using a codec (compressor-decompressor) repeated digital information about the picture can be eliminated and added back, ultimately reducing the size of the file Some codecs are lossy the information gets thrown out, while others are not The frames within a GOP get labels based on how much of the image detail is contained within p. 67 Slide 21 Group of Pictures Groups of Pictures (or GOP) are a successive series of frames grouped together An I frame (intra picture) contains all the image sample detail needed and is an anchor or reference frame for the other images around it A P frame (predicted picture) contains information on how the current frame has changed from the previous frame AB frame (bidirectional picture) looks both forwards and backwards and contains only the difference in data from both the previous and following frame p P age

8 Slide 22 Group of Pictures GOPs typically start with I-frames (but not always) The next frame can be another I-frame ProRes422 AVC-Intra 100 Avid DNxHD The next frame can be a B- frame or a P- frame DV MPEG-2 AVCHD Long GOP codecs are simply codecs that include I-, B- and P-frames An Open GOP shares information with either the previous or the next GOP A Closed GOP does not share information with any other GOP (potential for strobing) p. 67 Slide 23 Group of Pictures MPEG 1 / 2 is limited to 18 frames per GOP DVDs typically have frames per GOP MPEG-4 can have a 60-frame GOP or more The more I-frames, the bigger the file Adding P/B frames reduces file size but increases decoding complexity during random playback Slide 24 Overview Video Signal Elements Media Formats YUV Analog YP BP R Digital Sync Optical Disc The Digital Image Solid State Fields Acquisition Frames Making sense of digital file naming strategies GOP Best practices for digital legal video acquisition 8 P age

9 Slide 25 The Video Signal Media Formats Slide 26 STANDARD #4 The maximum recording time per recording media unit shall be 120 minutes (2 hours) unless otherwise specified by stipulation, rule, order or notice. p. 63 Slide 27 STANDARD #4 Random Thoughts This standard reflects the fact that DVD delivery is the current preferred playback media in court rooms. A Standard Play (SP) DVD provides a good balance of quality versus run time. Two hours of MPEG-2 video encoded at kbps fits on a DVD-5 (single layer 4.37 GB) disc. This standard could easily change if the standard deliverable changes 9 P age

10 Slide 28 STANDARD #5 Depositions shall be recorded at the standard play speed unless otherwise specified by stipulation, rule, order or notice. Random thought: No discussion has been decided as to the appropriate minimum standard for digital capture. You should be able to create a usable video that shows as much detail as a VHS tape (a.k.a. 352x240 MPEG-1) p. 66 Slide 29 STANDARD #6 Any format is acceptable for the purpose of recording depositions provided that a simultaneous back-up recording is made. Random thought: The videographer should be able to create an client-acceptable deliverable with the back-up recording. p. 63 Slide 30 VHS Developed by JVC standard format for consumer video recording Video Home System, launched in 1976 as a home entertainment system Format war: VHS (JVC) vs Betamax (Sony) Beta was technically better but VHS won the format battle 250 horizontal lines of resolution Still in use in some court systems p P age

11 Slide 31 Super VHS Improved resolution to 420 lines Separated luminance Y from chrominance C Poor market acceptance Major contribution was the popularization of the s- video connector p. 64 Slide 32 DV (Digital Video) 1996 Developed by consortium of the world s most powerful electronic companies. A product of cooperation, brought about a truly revolutionary era in video DV is a specific video standard IEC Dramatically better picture quality DV 520 lines vs. VHS 250 lines p. 65 Slide 33 Standard Definition Digital Tape MiniDV (Small or S-size cassette) Designed for consumer recording 520 horizontal line resolution 0.25 (6.35mm) wide magnetic tape Standard play of 60 or 83 minutes preferred Potential issues with long play / 83 minute tapes possible Panasonic DVCPro (Medium or M-size cassette) Designed for professional recording Similar to DV tape; records at 1.5x speed Sony DVCAM (Large or L-size cassette) No loss of quality in successive copying Superior signal to noise ratio p P age

12 Slide 34 High Definition Digital Tape Supported by Canon, Sony, Panasonic 0.25 wide magnetic tape Specialty HDV tape manufactured with higher tolerances to reduce dropout HDV records SP mode only Cannot support high bit rates and long record times Higher data requirements needs faster tape speed to store info HD tape playback equipment is more expensive than SD Just good to know Slide 35 STANDARD #50 Upon the conclusion of any original recording media of the deposition, the videographer shall immediately activate the record inhibit of the media. This applies to tape or solid state media Compact flash cards have no record inhibit p. 69 Slide 36 Digital Video Disc Also known as digital versatile disc DVD-R DVD-RW DVD-RAM DVD+R DVD+RW Recorder writes by pulsing a laser to heat the dye layer (photosensitive material) and burns oval pits into disc All use UDF--Universal Disk Format ISO 9660 file system DVD Recording Modes XP, SP, LP, SLP Use Standard Play (SP) 120 minutes for deposition work Duplication vs. Replication Duplication changes dye color while replication has physically stamped pits Important Note: all must be finalized p P age

13 Slide 37 Digital Video Disc 540 lines of resolution -- MPEG-2 is basis of DVD video MPEG-2 Video is stored on DVDs and formatted for two mutually incompatible television systems: NTSC or PAL/SECAM Regional Codes: Controls the geographic distribution (eight regions) of DVDs Prevents playback of certain discs in certain geographic regions DVD Players - 1st gen had playback compatibility problems but by 2003 most drives that could read both DVD dash & plus p.66 Slide 38 Disc Technology 1 st: CD, 2 nd: DVD, 3 rd: Blu-ray Disc (BD) HD DVD dead on-arrival CD, DVD: Red laser technology (longer wavelength) DVD: 4.7 Gb single layer, 8.5 Gb dual layer, 10.8 Mb/s bit rate Blu-ray: Blue laser technology (shorter wavelength) Single layer 25 Gb single layer, 50 Gb dual layer, 36 Mbps Shorter the wavelength the more precise the beam spot that contacts the disc, allows for more data to be stored on disc Just good to know Slide 39 SD / SDHC / SDXC cards Compact Flash (Type I & II) Cards SXS cards Sony P2 cards Panasonic Solid state drive Various encoding codecs DVCPRO P2 XDCAM AVCHD / AVC H.264 MPEG-2 Accelerated Work Flow Solid State Media p P age

14 Slide 40 Solid State Media Random Thoughts Compact flash, SDHC and SDXC cards often use either FAT32 or exfat (extended File Allocation Table) file systems, which result in split files during long capture. Some cameras (re: Sony HXR-NX5u) will split the audio and video files at different points when laying down the file, resulting in gaps in the audio record if the files are not joined together in a post production process. You must use special software to join the clips together prior to encoding for delivery. Windows XP does not ship with SDXC dll files and must be updated with a free dll download to properly handle the cards. You re, of course, aware of the fact that all Windows XP machines should be scrapped as of April 2014 Slide 41 Solid State Media Random Thoughts Read speeds can dramatically impact how long it takes to copy or move the files from the media to a secondary drive (like an external backup). Always buy the fastest read/write speeds you can afford within a given price point for a piece of media. Typically, the more you pay, the better the specs of the card. Time is not free, and saving $20 on a slow card is not worth it. Slide 42 Solid State Media Random Thoughts Solid State Drives (SSDs) are very fast input and output buckets. SSDs are optional on computers and are recommended for many HDMI / HD-SDI / 3G-HDI external recorders. The cost per GB of an SSD is more expensive than a spinning hard drive, but the prices are constantly going down. Keep track of the price per GB; they ultimately will be very cheap. Buy during sales, being mindful that specs count. Always bring in enough room to retain at least 12 hours of your preferred format of media. If you re busy, bring a lot more. Read the specs for the recording devices. Do not skimp on their recommendations. There are cheap SSDs. They may not be appropriate for video. 14 P age

15 Slide 43 Solid State Media Random Thoughts There are two approaches to managing video with solid state media at the deposition: Bring enough media in to maintain a copy on the media and transfer back at the shop Bring in a storage system and transfer the media at the deposition, then reuse the media at the deposition The most streamlined workflow occurs when a day s media is in one container, which eliminates having to switch out containers at the office and allows for batch processing of a day s work in one setup. Slide 44 Solid State Media Random Thoughts If you bring a computer to the deposition and you shoot cards, look into a clip management program like Imagine Software s Shot Put Pro. It can make simultaneous backups to multiple drives and creates a write log for verification. Buy computers with USB 3.0 or Thunderbolt ports for fast card dumps. Buy HDD (spinners) with a minimum rating of 7200 RPM and one or two different port options; hopefully with USB3.0 or Thunderbolt. I currently like buying 1 TB drives for depo use. They seem to last and are useable for multiple days. I carry 3 to every depo. Keep your source files and your encoded files on two different drives during processing. This reduces the number of reads a given hard drive head has to do, speeding up the overall process. Slide 45 Solid State Media Random Thoughts I record 480p to two 64GB SDXC cards, which hold 4:43 hours of video with a DV25 codec. I record 480i to a compact flash recorder. I backup the SDXC card during the depo to two different drives (A&B). I back up the CF card to a card storage unit. This copy gets tossed out after I do all my encoding and QC. I read from drive A, transcode, and then deliver the files to drive B. I end up with a complete set of source and encoded files on drive B, which are then easily transferred to their final resting place(s). Once drive B is backed up successfully to all locations, the copy on drive A is deleted, as are the backup copies. 15 P age

16 Slide 46 Overview Video Signal Elements Media Formats YUV Analog YP BP R Digital Sync Optical Disc The Digital Image Solid State Fields Acquisition Frames Making sense of digital file naming strategies GOP Best practices for digital legal video acquisition Slide 47 Panasonic AG-AC130a/160a File Structure Characters 1-3 Unique On/Off Cycle, sequentially numbered Characters 4-5 Unique two digit identifier Characters 6-7 Sequential clip counter, ~4 GB GB Max Characters 8-11 File Type This example shows three On/Off cycles, with seven additional files created automatically because the file exceeded the max size. Slide 48 Panasonic AG-HMC80 File Structure Characters 1-3 Unique On/Off Cycle, sequentially numbered Characters 4-5 Unique two digit identifier Characters 6-7 Sequential clip counter, ~4 GB Max Characters 8-11 File Type This example shows three On/Off cycles, with five additional files created automatically because the file exceeded the max size. The last clip is out of sequence (a common problem) Mimics AG-AC130 style, has larger maximum file size 16 P age

17 Slide 49 Panasonic HPX170/250 File Structure COMMENTS P2 has unique file structure Audio and video are recorded in different files Naming schema for video and audio related File splits for video are different than file splits for audio Professional Level NLE systems easily ingest P2 schema Consumer Level NLE systems may not easily ingest schema Slide 50 Panasonic HPX170/250 File Structure VIDEO Slide 51 Panasonic HPX170/250 P2 File Structure AUDIO 17 P age

18 Slide 52 Sony HXR-FMU128 File Structure Duplicate of Sony NX5U file structure External recorder typically used with Sony HXR- NX5U camcorder Slide 53 Sony HXR-NX5U/NEX-FS100 File Structure Characters 1-3 Camera identifier Characters 5-8 Sequential clip counter, 2.1 GB Max Characters 9-12 File Type (We think) this example shows five On/Off cycles, with two additional files created automatically because the original file exceeded the max size. Slide 54 Compression and Storage Requirements Standard definition camcorders compress 5:1 High definition camcorders can compress :1 High definition can be very lightly compressed as well, resulting in really big files. Dominant storage medium for legal video has been the DV tape but now changing to file-based recording At 25 Mbps, about 13.1 GB per hour are captured with standard definition DV codec captured in an AVI-T2 wrapper p P age

19 Slide 55 Compression and Storage Requirements HD storage requirements vary widely depending on bitrate and codec. Some MPEG-4 codecs will capture a larger picture in a smaller file, mainly because of the better compression efficiencies of some codecs. On the other hand, Apple ProRes 422 HQ consumes over 120 GB per hour of video. Compression can severely limit the amount of color information available to make fixes. If you re capturing AVCHD white balance often, because it takes a lot of horsepower to fix the color in post, and there s not a lot of information left to fix the image exactly right. p. 67 Slide 56 Media Formats Random Thoughts An analog NTSC SD source is always interlaced, fps, and varies in resolution, with composite being the lowest quality DVD MPEG-2 is stored as Video Object (VOB) at about 2 GB per hour on the Standard Play setting. Capturing to a DVD recorder will almost always create an interlaced, variable bitrate product FireWire capture is almost always 480i when done in standard definition. HDV is the only HD format that can be captured via FireWire in 720p or 1080i Slide 57 Best Practices Legal Video Capture Progressive is the better choice for capture (and delivery) of legal videos, particularly when delivering MPEG-4 for tablets. 60p is slightly preferred over 30p 60p is easy to make 30i if it s needed Interlacing from progressive source is easier than deinterlacing (going from interlaced to progressive) 30p is not a bad choice it s just not as good a choice as 60p 19 P age

20 Slide 58 Best Practices Legal Video Capture Preferences: Progressive > Interlaced Digital over (most) analog A reasonable balance of quality versus file size ProRes 444 is really nice, but do you really want to use up that many GB for a talking head that may ultimately end up as an MPEG-1? Component > S-Video > Composite 480p > 480i 720p60 > 720p30 > 1080i p <> 720p file size versus quality Slide 59 Mastering The Video Signal Questions? Bruce D. Balmer, MBA, CIRM, CLVS, CCVS, CME legalvideo@compuscripts.com 20 P age