Subtitling Web Video
Screen has developed innovative solutions to the production and display of quality subtitles for OTT & Web content.
Most standard web-video players use a simple timed-text file for OTT subtitling (e.g. SRT for YouTube, DFXP for Flash and QuickTime and SMIL for Windows Media Player), all of which are easily created in WinCAPS and/or MediaMate. However these solutions rely on this timed-text file being interpreted by the video player and the appearance of the subtitles can therefore differ between players and between devices – with positioning being particularly inconsistent. (Early implementations did not even overlay the subtitles within the video picture area, instead positioning text within a black box beneath the main video.) This means that the subtitle-author cannot be sure as to how the subtitles will appear in font, style or position. Therefore for accurate and consistent presentation these uncertainties need to be overcome.
Screen’s new subtitle overlay layer solution for web video involves not only the engine to create the subtitles but also a means to display them in the player. It’s an image based approach to ensure consistent presentation of the subtitles on all players while also improving the visual quality of the subtitles on low-bandwidth connections as the subtitles are not subject to the same compression as the underlying video picture.
Open-source Java plug-ins for each media player allow clients to implement this form of subtitling into their website systems with ease. The plug-in displays the PNG subtitle sequence as an overlay to the main video in synchronisation with the video playback. The subtitles can be turned on/off at the viewer’s control and will even allow the user to select from multiple languages where available.
Streaming from a server – MediaMate
Screen has developed a method for served web video playback that ensures that subtitles are always displayed in the style intended regardless of the player – while allowing the viewer to select from several language streams (and off) without the need to re-encode the video or host multiple copies.
Screen’s MediaMate file-based open subtitle encoder converts a standard subtitle file (per language) into timing data and images for the target resolution(s) applying an EDL if necessary to adjust for web-specific edits or commercial breaks. The resultant PNG and XML files are hosted on a web-server ready for use; for extra flexibility this web-server need not be the same as that hosting the video.
- producer has full creative control over style and position
- text is clear (not affected by the video compression)
- allows viewer to select language or turn captions off
- uses standard subtitle file formats
- can automatically adjust broadcast version for the web via EDL
Screen’s Polistream system can also produce the same PNG and XML output as part of a live transmission – for use when the completed programme is later made available over the web (for playback from the host server). To display subtitles as part of a live web stream read on …
Live streaming – Polistream
Subtitles for live web streams are not easily supported by web-video players and the variable latencies in web delivery make synchronisation very difficult. If subtitles for live streams are required then hitherto they have been burnt-in as open subtitles prior to encoding as a web-stream. However Screen has now developed its own synchronisation method to enable accurately timed subtitles to be delivered on live web-video feeds – as closed subtitles in one or more languages, without the need to encode multiple streams.
Screen’s innovative solution (a TVB Europe Best in Show award winner at IBC 2014), uses Polistream to add a time-stamp to the video as it’s encoded – then using code added to the player to analyse the timing data and display the correct subtitle (using the same image-based approach described above – except that the images are also created by Polistream). This technique has initially been successfully demonstrated using an Elemental HLS encoder with output to PC, Android and iOS – integration with encoders from other manufacturers is also under consideration.
A broadcaster’s Polistream system can now be easily upgraded to add an interface to their streaming video encoder so that real-time subtitling on any live broadcast is also conveyed on the simulcast web output. The same method can also be used with “live TV on the web” to deliver multi-language subtitles for pre-recorded programmes.
This approach ensures reliable subtitles that are always in sync with the video regardless of the video player or platform – even when live video rewind or pause/resume is used.
The following links show implementations of this new subtitle overlay layer solution for various Internet media players. The players used are all simple versions, created on top of the generic publicly available sample players with the subtitling functionality foremost in mind rather than the aesthetics of the control bar. We recommend viewing in Chrome or Firefox rather than Internet Explorer and of course some of these players will not work on mobile devices.
Download the full Screen White Paper on OTT Subtitling.
- 3D Depth Mapping
- Automatic Subtitle Timing
- Automation Suppliers
- File Based
- Monitoring & Logging
- Speech Recognition for Subtitling
- Spoken Subtitles and Audio Description
- Subtitle Pass Through and Transcoding
- Subtitle Preparation Software
- Subtitle Transmission Systems
- Subtitling for 3D
- Subtitling Web Video
- Subtitling with File Based Workflows