Maintaining quality in file based video

Tom Perry – Tektronix Bristol

Maintaining Quality in File Based Video

1

2

Outline

What is file-based video?

Video compression

Challenges of file-based video quality control

Automatic quality control for file-based video

2 Vision08, 03.2008 Maintaining Quality in File Based

What is File-Based Video ?

3

4

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

Vision08, 03.20084 Maintaining Quality in File Based

5

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…


6

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

Vision08, 03.2008 Maintaining Quality in File Based6

7

Broadcast technical challenges

Vision08, 03.20087

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

Maintaining Quality in File Based

8

Typical Workflow


9

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.


10

Storage

Encoded files are stored in nearline storage

High resolution master files can be transcoded and repurposed for delivery to different customers


11

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


12

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

13

14

Typical Applications of different codecs

Vision08, 03.200814

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


15

Typical Applications of different codecs

Vision08, 03.200815

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


16

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


17

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


18

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


19

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


20

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


21

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


23

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)


24

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.


25

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


26

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


27

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)


28

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


29

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


30

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 ofFile Based Video Quality Control

31

32

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


33

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


34

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


35

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


36

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, 03.200836

188 byte packets(or 204 bytes)

HeaderPID CRCVideo

Elementary StreamAudio

Elementary StreamMeta-data

Transport Stream data -tables, etc.

Video AudioTables Meta-data


37

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, 03.200837

188 byte packets(or 204 bytes)

PID CRCVideo Elementary Stream

bit errors during encoding


38

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


39

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


40

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


41

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


42

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 forFile Based Video

43

44

Broadcast technical challenges

Vision08, 03.200844

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


45

File-based Auto QC at ingest

Vision08, 03.200845

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


47

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


48

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


49

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


50

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


51

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


52

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


Questions?

53

Documents

Maintaining quality in file based video