maintaining quality in file based video
TRANSCRIPT
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Tom Perry – Tektronix Bristol
Maintaining Quality in File Based Video
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Outline
What is file-based video?
Video compression
Challenges of file-based video quality control
Automatic quality control for file-based video
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What is File-Based Video ?
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Brave new digital world
New broadcasters– not just TV, satellite, cable, but also– wireless– VOD– internet– podcasters
New, very different technical requirements– new codecs– new formats, resolutions, frame rates, quality levels– re-purposing and re-encoding
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Broadcaster Technology Challenges
Content file integrity– Correctly encoded on ingest– Ensure files are not corrupted during
movement, copying and transcoding processes
Support multiple delivery platforms and formats
– Terrestrial DTV, Satellite, Cable– Mobile video – Streaming– MPEG-2– HD– Podcasts, internet (H.264, MPEG-4,
VC-1), VoD (H.264) – More…
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Changes in Workflow
Increase in compression and decrease in hard disk prices
Exponential growth of the Video Server market globally
Broadcasters are turning to ingest, manage, store and playout their video assets from Video Servers
Complex distribution via terrestrial, satellite, cable, internet and mobile
Content is being re-purposed at different resolutions and frame rates, using new codecs and at different bit-rates, with different technical requirements
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Broadcast technical challenges
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Broadcasting Key Challenges
Reliably store, aggregate and distribute more content in more formats for new distribution pathsMastering New Technologies:• File based Workflow• HD, H.264, MPEG4, VC1, VOD, Video over IP
Challenges • Explosion of content and formats• Need to QC ingested content from multiple sources• Human QC not sufficient and not 24/7
Content Delivery
Ingest Edit
Schedule Playout
Ingest Servers
Edit, Schedule & Monitor
Playout Servers
Terrestrial
VOD
IPTV
Archive
News Feeds
Sport
Movies
Post production
File based workflow Satellite
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Typical Workflow
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Ingest
Management software controls tape or line ingest
Serial Digital Video signal is encoded to a compressed format
SDI is monitored on waveform monitor for gamut errors and audio peaks.
Compressed video is wrapped with audio tracks, timecode information and metadata
Encoded and wrapped file is played back to check quality. Measurements made on waveform monitor.
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Storage
Encoded files are stored in nearline storage
High resolution master files can be transcoded and repurposed for delivery to different customers
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Archive
Material is moved to the archive after playout or if ingest is advanced a long time of playout
Material is restored from the archive
Content metadata can be searched and relevant clips restored
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Playout
Today there can be many outputs from a broadcaster
– Streaming Web site– IPTV Delivery– HD/SD Traditional Broadcast– 3G Mobile delivery
All these components require file based QC
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File-Based Video Compression
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Typical Applications of different codecs
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Video Codec Typical applications (new)
MPEG-2 Broadcast, cable, VOD, DVD
H.264 / AVC / MPEG-4 Pt 10
Broadcast, cable, VOD, HD, Internet, HD video disks*
WM9/VC-1 Broadcast, HD, Internet TV, HD video discs – Blu-Ray
DV/DVC-Pro 25/50 Broadcast, Acquisition, Editing
MPEG-4 Pt 2 Mobile
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Typical Applications of different codecs
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Video Codec Typical applications (new)
DNxHD/VC-3 Editing, Broadcast Playout
AVC-Intra Acquisition, Editing
Pro-Res Editing, iTunes
JPEG 2000 D-Cinema, broadcast internal use/archive
DVC-Pro100 Acquisition, Editing, Broadcast Playout
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MPEG-2: History & Use
MPEG-2 is for the generic coding of moving pictures and associated audio
MPEG-2 (1994) is the designation for a group of coding standards for digital audio and video
Agreed upon by MPEG (Moving Pictures Experts Group), and published as the ISO/IEC 13818 international standard
Typically used to encode audio and video for broadcast signals– Direct broadcast satellite & terrestrial digital TV– Cable TV– Video on demand (cable & IP)– DVD
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MPEG-2: Profiles
Abbr. Name Frame Types
Colour Format
SP Simple Profile I, P 4:2:0
MP Main Profile I, P, B 4:2:0
422P 4:2:2 Profile I, P, B 4:2:2
SNR Single to Noise Ratio I, P, B 4:2:0
SP Spatial Profile I, P, B 4:2:0
HP High Profile I, P, B 4:2:2
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MPEG-2: Levels
Abbr. Name Frame Rate (Max)
Pixel/Line(Max)
Lines (Max)
LL Low Level 30 352 288
ML Main Level 30 720 576
H-14 High 1440 30 1440 1152
HL High Level 30 1920 1152
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MPEG-2: Typical Configurations
SDTV, DVD– MP@ML, 720 × 480 or 720 × 576, 4:2:0 colour format, 29.97 or 25 fps
HDTV– MP@HL, 1920 × 1080i or 1280 × 720p, 4:2:0 colour format, 30 or 60 fps
Ingest (Sony IMX I-Frame Only)– 422P@ML, 720 × 480, 4:2:2 colour format, 30 or 60 fps
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VC-1: Use
Implemented by Microsoft as Windows Media Video (WMV) 9 Advanced Profile, allowing WM content to be delivered over traditional broadcast and wireless infrastructures
Mandated codec for next-generation DVD (Blu-ray) – all devices will be capable of decoding VC-1
Used in Taiwan on their proprietary DVD format – “forward versatile disc” (FVD)
Microsoft has designated VC-1 as the Xbox 360 video game console's official video codec
Now a SMPTE standard
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VC-1: Selected Profile & Level Combo’s
Profile Level Max Bitrate
Example Use
Main Medium
10 Mbps 720 x 480 @ 30 Hz (480p)720 x 576 @ 25 Hz (576p)
Main High 20 Mbps 1920 x 1080 @ 30 Hz (1080p)
Advanced L1 10 Mbps 720 x 480 @ 30 Hz (NTSC-SD)720 x 576 @ 25 Hz (PAL-SD)
Advanced L3 45 Mbps 1920 x 1080 @ 24 Hz (1080p)1920 x 1080 @ 30 Hz (1080i)1280 x 720 @ 60 Hz (720p)
Advanced L4 135 Mbps 1920 x 1080 @ 60 Hz (1080p)2048 x 1536 @ 24 Hz
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AVC: AVC / H.264 Profiles
The AVC/H.264 standard defines four different Profiles: Baseline, Main, Extended and High Profile (which themselves are subdivided into Levels):– Baseline Profile offers I/P-Frames, supports progressive and CAVLC only – Extended Profile offers I/P/B/SP/SI-Frames, supports progressive and
CAVLC only – Main Profile offers I/P/B-Frames, supports progressive and interlaced,
and offers CAVLC or CABAC – High Profile (aka FRExt) adds to Main Profile: 8x8 intra prediction,
custom quantisation, lossless video coding, more component formats (4:4:4)
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AVC: Benefits
Is an “open standard”, compared to closed formats, like Microsoft's Windows Media
Performs significantly better than any prior standard can, under a wide variety of circumstances in a wide variety of application environments
H.264 can often perform radically better than MPEG-2 video—typically obtaining the same quality at half of the bit rate or less
Can be carried by MPEG-2 Transport Streams making it increasingly used in HD VoD applications.
AVC-Intra is a Panasonic P2 implementation of Intra frame coded AVC. Gaining popularity for acquisition and editing.
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DNxHD/VC-3
Avid’s DNxHD is a HD codec technology engineered to create mastering-quality HD media at reduced bit rates to allow HD editing and production using SD infrastructure.
In January 08 it was approved to be compliant with SMPTE 2019 VC-3
There is support from EVS and Omneon amoungst others for playout.
Image © Avid.com
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DNxHD Key benefits
– Optimal mastering picture quality
– Reduced storage requirements – Enables real-time HD sharing and collaboration – Improved multi-stream performance
– Specifically engineered for multi-generation compositing and post production
– Full frame raster sampling
– Choice of 8- or 10-bit sampling as well as three user-selectable bit rates
– Open standard: HD Codec source code is licensable free of charge
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Apple Pro Res 422
Unlike DNxHD, ProRes 422 provides full functionality at advanced resolutions (2K and 4K cinema) and SD.
It is DCT based, and is therefore simpler to decode than distribution oriented formats like H.264.
Full-width 1920x1080 and 1280x720
4:2:2 chroma sampling
8 and 10-bit sample depth
I frame-only encoding
Variable bit-rate (VBR) encoding
Normal 145 Mbit/s and High-Quality 220 Mbit/s for HD resolution
Normal 42 Mbit/s and High-Quality 63 Mbit/s for SD resolution
Fast encoding and decoding (both at full size and half size)
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Wrappers
Ingest and Playout are in transition– Analogue to Compressed Digital
Methods of storing video are changing– Tape to File based stored on Server
Many different new formats– Terrestial, Satellite, Cable, VoD, IPTV– QCIF, CIF,SD, HD,– MPEG-2, MPEG-4, H.264/AVC, VC-1– Different bitrates, GOP, Audio etc
Many different wrappers– MPEG TS– MXF– QuickTime
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MXF – Wrapper
Media eXchange Format
Developed as a global wrapper format for all video, audio and metadata
Specification is layered. “OP1A” configuration is most commonly used today (simplest implementation of MXF)
File interchange for networked AV file distribution
Format independent– Picture Size – Interlaced or Progressive– Audio Sampling Rates
Wraps all formats– Current and future formats– Metadata only files allowed – Compressed and uncompressed
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QuickTime – Wrapper
QuickTime is a multimedia technology developed by Apple, capable of handling various formats of digital video, sound, text, animation, music, and immersive panoramic (and sphere panoramic) images
Openly documented and available for anyone to use royalty-free
The most recent version is 7
Now features complete MPEG-4 compliance, and support for H.264/MPEG-4 AVC codec
Fifth generation iPod decodes H.264 wrapped as QuickTime
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Challenges ofFile Based Video Quality Control
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Video Quality Control
Video QC is a delivery requirement by many broadcasters. QC Operators would be looking at:
– Black and white level– RGB Gamut and possibly composite gamut– Number of audio channels, level and loudness
peaks, phase– Picture action and graphic safe areas in all
deliverable aspect ratios– Creative quality and attached metadata such
as program duration, commercial breaks and clock details
– Video blanking– Timecode pressence and continuity– General picture quality, standards conversion
and compression artefacts, tape drop out
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Increasing
abstraction
File-based video testing ‘abstraction stack’
Level of video abstraction stack
File organization and structure
Video and audio quality
Broadcast play-out center requirements
Video & audio elementary stream
MPEG-2 Transport Stream
Baseband digital
Analog signals
Level of video abstraction stack
Types of checks/tests
File organization and structure File associations, meta-data
Video and audio quality Subjective assessments and objective measurements
Broadcast play-out centre requirements
Measurable limitations to be suitable for transmission
Video & audio elementary stream Syntactical/logical checks
MPEG-2 Transport Stream Compressed representation – abstracted time
Baseband digital Direct timed correlation to physical signals
Analog signals Physical signal, direct measurements
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QC from an “analogue” perspective
Standard analogue signal tests:– presence and level of
synchronisation signals– video gamut, signal legality– audio levels– line and frame timings
Standard solutions:– waveform monitors– PPM/VU audio meters
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Baseband Digital (SDI)
No direct correlation to analogue signal, e.g.
– video data needs to be extracted to re-construct ‘analogue’ signal
– synchronization ‘signals’ are code-words in data stream
Example SDI errors:– signal jitter, level errors –
bits misinterpreted
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Structure of MPEG-2 Transport Streams
Inside packetization and CRC data of MPEG-2 TS:
Video and audio data can be tens or hundreds of Mbytes – interleaved in time through-out the MPEG-2 TS packets
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188 byte packets(or 204 bytes)
HeaderPID CRCVideo
Elementary StreamAudio
Elementary StreamMeta-data
Transport Stream data -tables, etc.
Video AudioTables Meta-data
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Elementary Streams
Video and audio compression separate from TS– complex
• and increasingly so with MPEG-4/AVC
– generate their own types of errors
Legal TS can have incorrect/illegal ES within
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188 byte packets(or 204 bytes)
PID CRCVideo Elementary Stream
bit errors during encoding
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Elementary stream Bit Error Example
A single bit error in a single block in a single frame
NOT spotted in play-out centre– despite a ‘full’ QC being done i.e.
• base-band tests• TS tests• visually watched by QC personnel
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Bit Error Example continued
Error smoothed over by the advanced decoder in play-out centre
– Set-top box crashed– broadcaster thought end-customers
were having ‘finger trouble’
Playing the clip does not guarantee encoding
– Professional decoder has large buffer– Decoder may “mask” errors– Bitrate, GOP interval, colour sample
configuration cannot be seen
The syntax of the compression must be checked
Errors detailed in the report from Tektronix Cerify
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Good but still no good
Legal and syntactically correct - but not correct for the broadcaster:– broadcaster wants 720x608 resolution to include some of the vertical
interval but the video has been supplied/encoded at 720x576– English audio is required to be on channels 1 & 2 (Spanish on 3 & 4) but
these have been swapped– the peak bit-rate should be 4.5 Mb/s, but actually goes to 4.6Mb/s– The MPEG is sampled 4:2:0 instead of 4:2:2
These are issues that are very difficult to “see” by the QC operator
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File Based video Quality Control
File Based Video QC Application Challenges– Traditional video T&M only checks baseband (luma/chroma/signal) levels
in analogue and digital video streams– File-based video is different. It must be checked for
• Correct Encoding Syntax – at digital level, audio/video must be encoded without errors, so it plays out correctly at the Customer’s STB / playout device
• Correct Parameters – audio/video bitrates, GOP structure, Color-space, Color depth, Frame size, Frame rate, Aspect ratio, Quantization levels
• Correct Baseband and Quality levels - analog parameters for Signal levels, Luma, Chroma, Gamut and Quality levels of Black frames, Blockiness, Loss of audio, Audio clipping, Video/Audio playtime
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Human Quality Control Challenges
Human QC/play-out testing is time consuming and expensive
Visual/audio errors are easily missed with human play-out– just by blinking or losing concentration for a second– different skill level/experience/training of testers
Simple errors – human may not get constraints correct
Consistency – Cannot repeat exactly the same test on content, day after day, week after week
Person cannot easily look inside the file for example:– standard used for compression for video, audio– bit-rates of video, audio and overall– visual quality ...
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Automatic Quality Control forFile Based Video
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Broadcast technical challenges
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Broadcasting Key Challenges
Reliably store, aggregate and distribute more content in more formats for new distribution pathsMastering New Technologies:• File based Workflow• HD, H.264, MPEG4, VC1, VOD, Video over IP
Challenges • Explosion of content and formats• Need to QC ingested content from multiple sources• Human QC not sufficient and not 24/7
Content Delivery
Ingest Edit
Schedule Playout
Ingest Servers
Edit, Schedule & Monitor
Playout Servers
Terrestrial
VOD
IPTV
Archive
News Feeds
Sport
Movies
Post production
File based workflow Satellite
Auto QC
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File-based Auto QC at ingest
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Automation / Asset Management System
Video servers
GigE LAN
Ingest
API
Auto QC Controller
Auto QC Test Unit
Auto QC Test Unit
Auto QC Test Unit
User Web GUI
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File-based Auto QC at Turner
Turner Broadcasting– Location: Atlanta, GA– One of world’s largest broadcasters
Content– News– Shows– Cartoons– Movies
Format– Mostly MPEG-2 SD 5-25Mb/s– Moving to HD and MXF– Pioneers of MXF AS02
Existing QC– QC personnel sample batches of content– 3x 8hr Shifts/day– Rely on some content being checked at source
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File-based Auto QC at Turner
Requirement– Need to cover 12 channels of content– Initially to supplement then– Eventually to replace manual QC– Each up to 24hrs of new material / day per channel
Video Servers– Omneon Spectrum
Automation– ProBel Morpheus Asset Management
Quality Control– 12x Tek Cerify units at ingest– Integrated using CeriTalk with Probel Morpheus– Installed July 07 – Feb 08
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File-based Auto QC at SBS
SBS – Broadcasts to Denmark, Sweden, Netherlands,
Luxemburg, Greece, Poland, Bulgaria, Germany – 40M viewers– Expanding services to Scandinavia and Eastern Europe– Broadcast Playout Centre in London
Content– Currently SD MXF wrapped MPEG-2 – Moving to HD and MXF
Requirements– 800 - 1000 hrs of content/week– Auto QC of ingested files from multiple providers– Expansion capability to HD– Fully automated broadcast flow
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File-based Auto QC at SBS
Solution– Systems Integrator: Wellen & Noethen – Asset Management system: S4M – Video Servers: GVG K2 – Auto QC: Tektronix Cerify – cluster of 5 units
integrated with the asset management system
Status– Went live Sept 07– Currently around 800hrs per week of 24/7 auto QC– Backed by some manual rechecking of content
identified by the auto QC as having problems
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File-based Auto QC at JCA
Vision08, 03.200851
UK based broadcast services– Encode and Format wide range of file based
video– For international broadcasters and production
companies world wide
Requirement– Reliable QC that could run automatically– Integrated into a file-based workflow– Needed to be suitable for many different
formats
Status– Cerify Auto QC– Around 10 – 50 hrs/week
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In Conclusion
Video is moving to file-based workflows File-based video can be in several different compression
formats and wrappers New compression types are more complex than MEPG-2 and
give much greater scope for errors Errors typically occur separately in the Elementary Streams as
well as in the meta-data - that is, there could be a perfectly legal and correct Transport Stream, but the video or audio Elementary Stream or meta-data is incorrect.
File-based video quality control presents significant challenges for human quality control
Automatic Quality control supplemented by some manual rechecking has now been successfully implemented at broadcasters in US and Europe
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Questions?
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