D2.3 Interim Report on Pilot Services - the School of Engineering ...

Problems with subtitle trans-coding1. Three line subtitle problemDuring the process of transcoding teletext subtitles to DVB subtitles RBB experienced afew difficulties. One immediate problem was the faulty presentation of triple-spacesubtitles. Triple space subtitles are only used in one regular programme originating fromone of RBB’s partner broadcasters. However, as this is the main nationwide newsprogramme at 8pm people were considerably irritated. In teletext the triple-space text isrealised by showing the first two lines as one teletext page and by instantly adding athird line as another page, but without removing the former one. The DVB subtitletranscoder did not accept the “do-not-remove” tag and deleted the first two lines oncethe third one was to be presented. Thus, only the third line was shown and most of thesubtitle information was lost for the viewer. Additionally, there was a text positioningproblem. The first two lines where presented in the middle for a few milliseconds, butthe third line removed the first ones and appeared left-aligned, so that the viewerexperienced not only fragmented but also jumping text.The transcoder manufacturer was able to avoid this faulty presentation behaviour bychanging the software into accepting the “do-not-remove” tag. Currently the triplespaceDVB subtitle presentation is much better, both the alignment and the entireness.2. “Jumping subtitles”Another faulty pattern that should not have occurred at all was what we call “subtitlejumping”. The picture below shows one example of this: the teletext subtitles are leftaligned both as a text block and concerning the single lines, the DVB subtitles arecentred and the lines are also centred. Something like this happened in different textpositions. However, there was not a regular pattern at first sight, it all happened in avery arbitrary way sometimes the positioning was right, sometimes not, so theimpression is of “jumping text“ which is very irritating. Nearly all the different textpositions of the teletext are presented in the wrong way in such an “irregular manner”.Of course the basic requirement was to have DVB-subtitles that looked exactly the samein terms of position as the original teletext subtitles. What was done to solve thisproblem was to analyse the teletext input going into the transcoder system. Seven suchfaulty positioning patterns were identified. The teletext authoring / editing system usesspace characters to position the subtitles on the screen. Transformation of this alignmentdata is not really working inside the subtitle editing software. The DVB ST Transcodercannot interpret several sequenced space characters. The solution is that the softwarereads and considers spaces and can calculate the subtitle position within the screenwidth. The manufacturer is now working on that problem. A possible forced centrealignment as a work around was not a satisfying option.Page 27