10 challenges facing the broadcast subtitle community
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GUIDE
10 challenges facing
the broadcast subtitle
community
and how new technologies can help resolve them
S
ubtitles are a valuable piece of the TV broadcast and streaming
ecosystem, and whether they add to the enjoyment of viewing by the
hearing impaired, or through language translation, they contribute in
some way to the operators’ business success. The industry is enjoying new
opportunities to monetise content on new platforms, and to new audiences,
but in reaching digital viewers media operators have to adopt new practices
and standards while, at the same time, reducing ‘per channel’ production and
transmission costs.
This guide highlights what Miranda sees as the ‘top 10’ challenges that operators and subtitling service companies face in the emerging digital media and proposes technology-assisted solutions which reduce the time and cost of subtitle production and distribution. The 10 challenges we will be focusing on are: 1 Reducing the time and cost of subtitle content creation and quality control 2 Converting broadcast subtitles for web and mobile streaming 3 Re-timing subtitle files for edited video content 4 Reducing the per-channel cost of dynamic ‘time of air’ subtitle output 5 Encoding closed subtitles in HD video 6 Simplifying DVB subtitling across multiple channels 7 Treating subtitles as part of a file-based media workflow 8 Subtitle creation for live and news programming 9 Creating and managing Audio / Video Description content 10 Monitoring subtitle streams in a multi-channel broadcast facility Note: In this document, the term “subtitles” means both closed captions and subtitles.
1 Reducing the time and cost of subtitle content creation and
quality control
The upward trend in the requirements for both hard of hearing and language translated captioned and
subtitled programing comes at a cost to the content production and delivery supply chain. Any technology
or workflow efficiencies that reduce the time and costs of subtitle production are thus very welcome.
The processes behind subtitle content creation and editing can be considered in two distinct areas –
subtitle editing and alignment, and subtitle quality control (QC). The first of these areas, the subtitle
creation, editing, and alignment to the spoken dialogue is the most resource intensive and thus the most
critical when looking for efficiencies. Traditional ‘craft’ subtitling requires skilled staff who understand the
subtleties of subtitle positioning, formatting and how to best précis the spoken words into the most elegant
and informative of subtitles. The opposite end of the subtitle creation spectrum produces ‘verbatim’ or
‘as-spoken’ subtitles – these are quicker to produce using fast typists or ‘voice to text’ software to allow a
‘re-speaker’ to listen to the program audio and ‘re-speak’ the subtitles into a subtitle workstation application.
If program scripts are available, and are accurate, these may be imported into the workstation to more
quickly produce a verbatim subtitle file.
The process of aligning or ‘timecoding’ each subtitle to the program manually is both time-consuming and
tedious – and this is an area where technology is well placed to reduce time and effort. Speech analysis
software provides the means to ‘auto synchronise’ subtitles to the program audio either as each subtitle is
created (‘TiGo’ or ‘time as you go’) or as a post-process once the program subtitle text has been prepared.
Although new to the market place, and limited initially to a defined set of languages, such ‘text to audio’
alignment technology is already proving to be very effective in reducing the time to produce ‘audio aligned’
subtitle files.
Traditional workflow Optimised workflow
‘Craft’ subtitling using time intensive dialogue Fast semi-skilled ‘verbatim’ subtitle input using speedy typist, script import
précis and manual subtitle positioning. or ‘voice to text’ re-speaking
Solution: Miranda Softel Swift Create subtitle workstation with the re-
speaking option
Manual subtitle alignment to video Deployment of speech analysis technology to auto-align subtitles to video as
they are created (TiGo mode) or as a post process (auto sync mode)
Solution: Miranda Softel Swift ReSync subtitle alignment tools
Visual QC checking of final subtitle file Background subtitle integrity checking of subtitles during the creation
process, and automated subtitle file QC checking at point of subtitle file
deployment
Solution: Miranda Softel Swift Create subtitle workstation (with integrity
checking) and Miranda Softel Swift subtitle QC application
Efficiencies in ensuring the quality of program subtitle files come from the application of automated QC tests both during and after the preparation of each subtitle file. During the subtitle creation process, a background ‘integrity’ checking application can provide prompt and effective feedback to the workstation user where quality indicators such as subtitle reading speed, presentation and inter-subtitle separation may be used to signal quality issues. A full workstation review mode is an essential feature of the subtitle workstation – this allows the program and subtitles to be played together as they would be seen by the viewer. There is scope for time-saving in this review process (which otherwise would take at least the duration of the program) by allowing the user to skip quickly through the captioned dialogue thus reducing the time to complete the program review process. When subtitle files are transferred from the subtitling team to a broadcast operations facility there is potential to replace the traditional manual task of re-checking the subtitles against the program video with an automated subtitle QC tool. It is not uncommon to find a mis-match between subtitle files and program episodes or between program timecode and subtitle file timecode. This tool analyses indicators such as audio speech to subtitle correlation and alignment (do the subtitles align to the spoken dialogue?), subtitle to scene change correlation (subtitles typically come on at the start of a new scene, and rarely cross over scene changes), and subtitle display regularity (it is rare for subtitles to be absent for long periods of time). Visual subtitle checking is time-intensive and an automated QC tool can quickly pay its way by reliably identifying the subtitle files which actually require re-checking. 2 Converting broadcast subtitles for web and mobile streaming Captions and subtitles are as important to viewers watching programs on web and mobile devices as they are to TV viewers, and in some cases even more so (watching content in a noisy environment for example). The challenge comes in knowing how and what subtitle file format is needed for each new media platform. In all cases there is a shared requirement for some sort of ‘timed text’ file but the format and file types vary widely. In the USA, there is a legal mandate for content owners and broadcasters to make available caption files in the new SMPTE 2052 IP caption file format. Many web and mobile streamer platforms require a caption file which is close in specification to a DFXP ‘timed text’ file, and in Europe the EBU are promoting the EBU-TT subtitle file format. The challenge to media operators is to decide where and when in the subtitle production and management workflow to produce these web and mobile derivative subtitle files. Professional subtitle workstations (such as Miranda Softel Swift Create) can export subtitle files in many different formats, and this is the easiest way for subtitle service companies to deliver multi-format subtitle files to their media distribution customers.
Content distribution facilities have the challenge of transcoding the master video into the wide range of compressed video streaming file formats required for the various formats. In this case it makes sense to produce the IP subtitle files as part of the video transcoding process. Transcoder suppliers frequently license subtitle plug-ins from subtitle specialists (such as Miranda Softel Swift vTX file-based subtitle processor) which offer the means to extract subtitles from the source video and create IP format subtitle files, or they can offer transcoding from one subtitle file format to another. Broadcast facilities often use powerful digital media asset management (MAM) platforms to store and publish content. MAM suppliers also typically offer Miranda Softel Swift vTX subtitle plug-ins to facilitate subtitle browsing, QC and multi-format subtitle file export. As a final option, a stand-alone Swift vTX subtitle file format transcoder offers the ultimate flexibility to be deployed as an independent tool in the media publishing process.
3 Re-timing subtitle files for edited video content
One of the biggest subtitling challenges is dealing with video and subtitle files which no longer match
– often video has scenes cut for online streaming, or the frame rate has changed, or content such as
advertisements are added, or simply the video timecode no longer matches the subtitle file. No one wants
to contemplate the costs of fully re-subtitling their video, and everyone hopes for a tool to fix their caption
files.
Looking at these scenarios in order of complexity, the first being ‘re-alignment’ - the case where timecode
on the video is not the same as when originally subtitled, or where the video frame rate has changed.
Subtitle re-alignment can be achieved using advanced subtitle file processing, which deploys a variety of
techniques to lock each subtitle back to the matching spoken dialogue. Typically, subtitle re-alignment is
run as a standalone task, or integrated into a production workflow or MAM system.
The second scenario is where the video has been edited since it was originally subtitled, but where an EDL
file (edit decision list) is available (‘EDL assisted re-alignment’). The valuable metadata in the EDL file can
be used by a subtitle processor to re-align each subtitle, after the first edit point, to the matching dialogue
in a video file. EDL assisted re-alignment is typically offered as part of a subtitle workstation (so that the
user may verify the amended subtitle file manually), or as a standalone automated process integrated into
production workflow.
The most complex of scenarios (‘fix-up re-
alignment’) where there have been video
edits, but no EDL file available, is naturally
the most challenging to solve. Technology
available today is able to get very close to
working out which subtitles are no longer
needed, and to re-aligning the remaining
captions, but the resulting ‘fix-up’ subtitle
file still requires manual checking.
The challenge The solution
‘Re-alignment’ – the video no longer carries the Post-process the subtitle file to produce a re-timecoded, re-aligned subtitle
original timecode, or the video frame rate has file. Run the task manually or as part of a media workflow process
changed Solution: Miranda Softel Swift ReSync
‘EDL-assisted re-alignment’ – video has been Post-process the subtitle file using the EDL file to re-align existing subtitle
edited, but an edit decision list file is available timings after the first edit point in the video. Run the task in a subtitle
workstation or as an independent process as part of the wider media
production workflow
Solution: Miranda Softel Swift Create with EDL processing, or Swift vTX EDL
‘Fix-up re-alignment’ – video has been edited Post-process the subtitle file to produce >90% accurate re-aligned subtitle
and all subtitle alignment lost file ready for manual checking in subtitle workstation
Solution: Miranda Softel Swift ReSync4 Reducing the per-channel cost of dynamic ‘time of air’ subtitle output
‘Time of air’ broadcast of subtitle files, aligned to the channel’s event playlist and to video timecode, is
a popular solution for single or multi-language closed (VBI or VANC encoding) or open (burnt onto the
video) broadcast subtitling. Teletext subtitle encoding into the ancillary space of SD or HD video serves
two purposes; the transmission of WST Teletext subtitles as part of a digital TV service, or as a means of
‘tunnelling’ subtitles in the video signal to a DVB bitmap digital subtitle renderer downstream at the video
encoding facility.
Cost savings can be achieved by choosing a subtitle play-out product, such as Miranda Softel Swift TX,
which uses ‘commodity’ IT server hardware and which scales from one to multi-channel in the same
server chassis. Multi-channel open subtitle rendering is the most cost efficient when deployed, using high
channel density SDI video keyer PC cards. In the case of Teletext and closed caption encoding into video,
external single or multi-channel encoder hardware is generally the most cost effective choice of hardware.
Operational costs for time-of-air subtitling may be minimized Tight integration simplifies
by ensuring tight integration between main and failover subtitle
processors and with channel automation. This automation operator supervision and
integration provides essential look-ahead schedule metadata to
ensures that operational
the subtitle processor so that subtitle files can be pre-loaded
and so that missing subtitle files can be flagged at the earliest issues are diagnosed and
moment. Tight integration simplifies operator supervision and
ensures that operational issues are diagnosed and solved using
solved using effective
effective built-in monitoring and service logging tools. built-in monitoring and
Capital costs are therefore most effectively reduced through
service logging tools.
the deployment of high-channel-density subtitle processors,
and optimum operation cost reduction is achieved through
the selection of a high-availability and tightly integrated subtitle
play-out platform.
Automation Media servers Digital asset management
Systems systems systems
Harris (inc Louth) Grass Valley Dalet
Miranda’s Softel Miranda Harris MassTech
Subtitling and
Captioning Pebble Beach Harmonic (Omneon) Evertz (Pharos)
Solutions
Partners Snell (ProBell) Pinnacle (Avid) Arvato Systems
XOR Media TMD5 Encoding closed subtitles in HD video
Whether encoding closed subtitles or captions into HD SDI video signals, or into HD video files, it is
important to understand the difference between the various closed subtitle and caption standards.
Closed subtitle and Use case
caption format
CEA 708 The North American standard for the carriage of closed captions in HD SDI video. Also used
to carry closed captions in video files in MXF SMPTE436M track or in the user bit space of an
MPEG program stream.
CEA708 also supports the carriage of international Unicode character sets and is deployed in
countries outside the US such as Korea.
OP47 Teletext OP47 carries up to the equivalent of 4 SD VBI lines of Teletext subtitle data in the VANC
ancillary space of an HD SDI video signal, or in an MXF SMPTE436m track within a video file.
Solution: Miranda Softel vFlex HD (encoding into HD SDI), and Swift vTX (encoding into video
files)
SMPTE 2031 2031 defines the way in which a full SD 16 VBI line Teletext service is carried in the VANC
ancillary space of an HD SDI video signal, or in an MXF SMPTE436m track within a video file.
Solution: Miranda Softel vFlex HD (encoding into HD SDI), and Swift vTX (encoding into video
files)
Miranda Softel MultiText Teletext The Teletext character set is limited to European and Arabic languages. Miranda’s Softel
subtitles MultiText format allows any international subtitle stream to be formatted as Teletext data
and carried as OP47 or SMPTE2031 data in HD SDI video signals or in video files. MultiText
subtitles may then be transcoded downstream into DVB digital bitmap subtitle streams.
Miranda’s Softel ancillary data processor, vFlex HD, enables the bridging, processing, encoding, and
regenerating of Teletext (OP47) and other ancillary data in HD video signals.6 Simplifying DVB subtitling across multiple channels
In the case of DVB subtitle processing, ‘less is more.’ There are significant power usage, rack space
and operational advantages in the deployment of a single server, multi-channel DVB subtitle system. The
Miranda Softel Swift TX DVB subtitle processor can generate over fifty individual language subtitle streams,
split across any number of program channels, from one standard IT rack server.
A multi-channel subtitle processor often has to support three very different modes of operation; playlist
synchronized play-out of subtitle files, transcoding of input video-embedded subtitles, and locally input
subtitle streams for live programs.
Play-list synchronization is most effective where the third
Miranda Softel Swift TX
party channel play-out platform supports an industry standard
subtitle control protocol such as Miranda Softel XAP. Tight DVB subtitle processor
integration between channel play-out and subtitle systems
ensures effective pre-loading of subtitle files, missing file
can generate over fifty
alerts, and real-time subtitle event play and stop messages with individual language
embedded ‘start at timecode’ controls (this removing the need
for complex routing of timecode to the subtitle system). subtitle streams from one
High channel density DVB subtitle processors, such as standard IT rack server.
Miranda’s Softel Swift TX system, offer proven operational
simplicity through proven performance, integration and easy to
follow services system health monitoring tools.
HD/SD OPEN CG
Single Channel
iTX Playout Video
Systems DVB
Dual Channel Compression
System Video with
Automation Quad Channel open
Control subtitles
+ Timecode
iTX Content
Store
Master DVB
Compression
System Video with
Subtitle
Files Standby
DVB
DVB Subtitles subtitles
SWIFT TX PLAYOUT7 Treating subtitles as part of a file-based media workflow
There are strong and positive arguments for binding subtitles to their matching video files at some point in the
media publishing workflow in advance of transmission. However, given the variety of media and subtitle file
formats in use, this is a real challenge. ‘Early binding’, as Miranda refers to this process, brings advantages to
the workflow such as the ability to QC-check subtitled video files, and can also reduce the need for subtitle
‘live binding’ transmission hardware and the operational resources required to oversee and manage time of
air broadcast systems. Miranda’s Softel Swift vTX file-based subtitle encoding application has been designed
and developed to accommodate the almost exponential combination of subtitle file formats, video file formats
and standards, video file wrappers, and subtitle encoding practices which are in daily use at broadcast and
streaming facilities around the world. Swift vTX is designed to operate in a number of use cases including
as a standalone subtitle
processor, embedded within
third party MAM and video INPUT OUTPUT
Video Video
transcoding products, or as Files Files
a slave to a wider file based
workflow, using Swift vTX’s Subtitle
Encoding
Subtitle
software API. Extraction
INPUT OUTPUT
Subtitle Task Subtitle
files Processes files
Core competencies required of a file-based subtitle encoding tool
Subtitle file handling • The ability to read all commonly used subtitle file formats
• The ability to transcode source to destination subtitle formats (e.g. closed caption
to Teletext)
• The ability to re-time a subtitle file frame rate between source and destination
• The ability to create new subtitle files, in any format, from subtitles extracted from
a source video file
Subtitle extraction • The ability to extract, frame by frame, subtitles or closed captions from a source
video file
• The ability to pass extracted subtitles to either the subtitle encode processor or the
file writing and export process
Subtitle encoding • The ability to generate standards-compliant subtitle video payloads for all
common subtitle and closed caption formats
• The ability to open and encode subtitles into all common video and video wrapper
file formats
• The ability to encode subtitles in MPEG program stream format for VOD
applications8 Subtitle creation for live and news programming Live programing creates one of the most significant and resource intensive subtitling challenges of all. By the very nature of live TV, most of the subtitle creation and output has to be handled dynamically during the original broadcast. There is no speech analysis technology available today which is able to automate the real-time subtitling process to the level of accuracy that is needed for broadcast TV. So, while we wait, the challenge is to find ways of generating live subtitles with the minimum of cost and effort. The two most common live subtitle input methods are stenography and re-speaking. Trained stenographers are common in the USA but less so elsewhere, so their use is limited. Re-speaking mixes the power of the latest ‘voice to text’ applications with the industry-specific features of the subtitle workstation to offer a relatively simple way to produce live subtitles using only semi-skilled operators. The operator, who has previously trained the application to his or her voice, listens to program audio and either repeats or summarizes the dialogue or commentary through a microphone to the subtitle workstation. The Miranda Softel Swift Create Live subtitle workstation supports subtitle re-speaking, but also a set of advanced features designed to simplify the process of live subtitle creation as far as possible. These include profanity filtering (black book of words never to be broadcasted), work sharing (the ability for multiple subtitlers to collaborate on the same content at the same time), and the ability to pre-load scripted elements of a live broadcast from a third party newsroom system. Swift vTX (early binding) and Swift TX (live binding) solutions may also be deployed to subtitle any pre-prepared elements of a news program. If the news programs, or any stories within the news programs, are to be repeated, then Miranda’s Softel Re-Sync re-alignment tools may be used to auto- correct the subtitle timings. Re-speaking mixes the power of the latest ‘voice to text’ applications with the industry-specific features of the subtitle workstation to offer a relatively simple way to produce live subtitles using only semi-skilled operators.
9 Creating and managing Audio/Video Description content
There is a slow but sure rise in the adoption of audio description (AD) services, which should not be a
surprise given the potential number of visually impaired viewers. The challenges involved in creating AD
content break down into three areas, scripting, recording and audio encoding. AD scripting is very similar
to the process of subtitle creation and editing except that the text is aligned to the quiet rather than the
conversational parts of each scene. The Miranda Softel Swift ADePT workstation software simplifies the
process of creating timecoded passages of AD script for each scene in a program, along with audio pan
and fade metadata in each case. A rehearsal mode allows the ‘describer’ to practice the narration and to
check the timings.
When it comes to the AD script recordings, there are three ways to go; there are professional describers
who are skilled at both script editing and narration, or facilities may have their own resident talent, or it
is possible to use text to speech software to automate the process. Miranda’s Softel Swift ADePT record
workstation takes care of the recording process and offers features to aid the narrator such as visual count
downs, before and during each passage, and the ability to choose the best ‘take’ from multiple recordings.
The AD audio is typically broadcast or streamed in one of two ways. Where bitrate is expensive, such as
for digital terrestrial TV, the AD audio is often transmitted on its own and mixed into program audio by
the consumer’s receiver using a dedicated low bit rate control signal. Otherwise, an audio mix of AD and
program audio is broadcast as an alternate stream. The Miranda Softel Swift ADePT Replay and Swift vTX
offer tools to create or broadcast these audio streams.
00:00: 10:00
Audio
Video DESCRIPTION SPEECH DESCRIPTION SPEECH
Audio
Description
AD
Script Audio
Video
ADePT Script ADePT
Record & Replay
The Miranda Softel Swift ADePT record workstation takes care of
the recording process and offers features to aid the narrator such as
visual count downs, before and during each passage.10 Monitoring subtitle streams in a multi-channel broadcast facility Multiple channels and multiple language subtitle streams make it quite a challenge to visually monitor subtitles at a digital TV play-out or turnaround facility. Viewers are fast to complain when subtitles go missing or are poorly aligned to the video; thus, operators are wise to invest in a tool which offers a mixture of both automated and visual subtitle stream monitoring. For visual subtitle monitoring, the choices are to leverage existing multi-viewer displays, or to create a dedicated display to show one or more realtime video streams along with all subtitle language streams. The Miranda Softel Swift Subtitle Monitor is a DVB subtitle monitor that addresses both these modes and more. Using a choice of PC or HD SDI display the operator can configure a set of display profiles which display a grid of X by Y video streams, each showing all or a subset of the language subtitles overlaid onto the video. The Miranda monitor has enhanced options to create automated loss of subtitle alerts, and to output the DVB subtitles streams for display on third party video multi-viewer displays. Example of Swift Subtitle Monitor Visual Display
The Miranda Softel Swift family of subtitling and closed captioning
solutions
The Swift range of subtitling and closed captioning solutions enables the creation, repurposing, encoding,
transcoding, insertion, monitoring and transmission of subtitles and closed captions in a wide array of file
formats while increasing reliability and productivity. Optimized for next-generation file-based workflows,
Swift products support subtitling and closed captioning for multi-platform delivery, across multi-language
feeds and in a complete variety of file formats.
MA N AG E C R E AT E D E S C R I BE INSERT T R A N S MI T MO N I TO R
• Quality Control • Caption/Subtitle file • Audio/Video • File• Encode
based • Multi-format • “At a glance”
• Task management •• Create description time-of-air multi-channel
• Bind-point control Edit
• Import
• Script
• Record
• Transcode
• Extract
transcode and
transmission
and multi-
language
• Export • Track
• Repurpose
• Live subtitle monitoring of
• Repurpose preparation • Open subtitle input & capture subtitle match
and alignment to
• digitizing
Browse-clip • Linearizer generation video
non-linear
for
• encode &data
VBI/ANC • Over 25 video
creation/ channels
re-purposing decode supported
Workflow
CG CG
About Miranda Technologies
For over 23 years, Miranda Technologies (www.miranda.com) has been a leading worldwide provider of
hardware and software solutions for the television broadcast, cable, satellite and IPTV industry. Its solutions
span the full breadth of television operations, including production, playout and delivery. With a wealth
of experience in delivering IT-based and traditional television systems, Miranda leverages its expertise to
create the highest quality solutions available and delivers, deploys and supports them with a company-
wide commitment to keeping the customer first. Miranda was acquired in July 2012 by St. Louis-based
Belden Inc. and is the cornerstone of its broadcast division. Belden is a worldwide leader in the design,
manufacture and marketing of cables, connectivity and networking products for many industries including
broadcast, entertainment, consumer electronics, education, transportation and industrial automation.
For more information, visit www.belden.com.
3499 Douglas-B.-Floreani, Montreal, Quebec, Canada H4S 2C6.
Tel: +1 800 224 7882 Fax: +1 514 333 9828
Abbey Gate, 57-75 Kings Road, Reading, Berkshire, United Kingdom RG1 3AB.
Tel: +44 118 952 3400 Fax: +44 118 952 3401
Belden is a trademark or registered trademark of Belden Inc. or its affiliated companies in the United States and other jurisdictions. Miranda, Softel and
Swift are trademarks or registered trademarks of Miranda Technologies Partnership. Belden Inc., Miranda Technologies Partnership and other parties may
also have trademark rights in other terms used herein. Copyright © 2013 Miranda Technologies Partnership. All rights reserved.You can also read
