Maintaining quality in file based video

Tom Perry – Tektronix Bristol Maintaining Quality in File Based Video

Outline
What is file-based video?
Video compression
Challenges of file-based video quality control
Automatic quality control for file-based video
Vision08, 03.2008 Maintaining Quality in File Based

What is File-Based Video ?

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

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…

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

Broadcast technical challenges Vision08, 03.2008
Broadcasting Key Challenges
Reliably store, aggregate and distribute more content in more formats for new distribution paths
Mastering 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 Servers Edit, Schedule & Monitor Playout Servers Terrestrial VOD IPTV Archive News Feeds Sport Movies Post production File based workflow Satellite Maintaining Quality in File Based Ingest Edit Schedule Playout

Typical Workflow Vision08, 03.2008 Maintaining Quality in File Based

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.

Storage
Encoded files are stored in nearline storage
High resolution master files can be transcoded and repurposed for delivery to different customers

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

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

File-Based Video Compression

Typical Applications of different codecs Vision08, 03.2008 Maintaining Quality in File Based 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

Typical Applications of different codecs Vision08, 03.2008 Maintaining Quality in File Based 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

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

MPEG-2: Profiles Vision08, 03.2008 Maintaining Quality in File Based 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

MPEG-2: Levels Vision08, 03.2008 Maintaining Quality in File Based 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

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

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

VC-1: Selected Profile & Level Combo’s Vision08, 03.2008 Maintaining Quality in File Based 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

AVC: MPEG-4 Standards
The MPEG-4 Standard is divided into many different sub-standards, below are some selected parts:
ISO 14496-1 (Systems), Animation/Interactivity (like DVD Menus)
ISO 14496-2 (Video), e.g. Advanced Simple Profile (ASP), as followed by XviD, DivX5, 3ivx...
ISO 14496-3 (Audio), Advanced Audio Coding (AAC)
ISO 14496-10 (Video), Advanced Video Coding (AVC), also known as H.264
ISO 14496-14 (Container), MP4 container format (uses the .mp4 extension)
ISO 14496-17 (Subtitles), MPEG-4 Timed Text subtitle format

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)

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.

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

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

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)

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

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

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

Challenges of File Based Video Quality Control

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

File-based video testing ‘abstraction stack’ Vision08, 03.2008 Maintaining Quality in File Based Increasing abstraction 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

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

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

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
Vision08, 03.2008 Header PID CRC Video Elementary Stream Audio Elementary Stream Meta- data Transport Stream data - tables, etc. Maintaining Quality in File Based 188 byte packets (or 204 bytes) Video Audio Tables Meta-data

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
Vision08, 03.2008 PID CRC Video Elementary Stream bit errors during encoding Maintaining Quality in File Based 188 byte packets (or 204 bytes)

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

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

Good but still no good
Legal and syntactically correct - but not correct for the broadcaster:
broadcaster wants 720x 608 resolution to include some of the vertical interval but the video has been supplied/encoded at 720x 576
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

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

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 ...

Automatic Quality Control for File Based Video

Broadcast technical challenges Vision08, 03.2008
Broadcasting Key Challenges
Reliably store, aggregate and distribute more content in more formats for new distribution paths
Mastering 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 Servers Edit, Schedule & Monitor Playout Servers Terrestrial VOD IPTV Archive News Feeds Sport Movies Post production File based workflow Satellite Auto QC Maintaining Quality in File Based Ingest Edit Schedule Playout

File-based Auto QC at ingest Vision08, 03.2008 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 Maintaining Quality in File Based

Vision08, 03.2008 File-based Auto QC at ingest Quality Control units Video Servers Automation Maintaining Quality in File Based

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

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

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

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

File-based Auto QC at JCA Vision08, 03.2008
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
Maintaining Quality in File Based

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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Maintaining quality in file based video

by Ronny72 on Jul 15, 2010

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Maintaining quality in file based video — Presentation Transcript