[FFmpeg-devel] DVB Subtitles

JULIAN GARDNER joolzg at btinternet.com
Tue Jun 17 23:14:56 CEST 2014


> From: JULIAN GARDNER <joolzg at btinternet.com>
>To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org> 
>Sent: Tuesday, 17 June 2014, 9:55
>Subject: Re: [FFmpeg-devel] DVB Subtitles
>> From: Reimar Döffinger <Reimar.Doeffinger at gmx.de>
>>To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org> 
>>Sent: Tuesday, 17 June 2014, 9:42
>>Subject: Re: [FFmpeg-devel] DVB Subtitles
>>On 17.06.2014, at 09:19, JULIAN GARDNER <joolzg at btinternet.com> wrote:
>>> Now a question for the list.
>>> If we take a HD stream, 1280x720 and have subtitles which are based on 720x576, what should we do if we have resized the video to 640x360, should we remap the subtitles to be in the same place or just leave them as is?
>>Without rescaling, remapping will improve things only minimally.
>>In containers like MKV this is solved by storing the original video size as dimensions of the subtitle stream, and we should do that.
>>For formats where this information can't be stored it might make sense to just refuse muxing if the subtitle dimensions do not match any of the video streams.
>Rescaling would be best, but do we have to create an image, rescale this and then OCR it?
>Remapping would be easier if the image was smaller than the available screen it will be shown on.
>maybe have a new option in the dvbsubsenc.c which tells the encoder the screen size it is being encoded to and we remap the x,y offsets as we know that dvbsubs are meant to be mapped to a 720x576 screen.
>ps. any takers on fixing the muxer?

Sorry for the OCR bit, thats another project!

On the DVB Subtitles, the problem with scaling is that each region would have to be scaled seperately and then remapped and as I am not looking at overlaying but reencoding and adding to the transport stream this would be a big undertaking.

So the question is how do i scale the individual dvb subtitle regions?, i have tried "[0:v] scale=-1:576 [vid],[0:s] scale=-1:288 [sub]" in my filter but this does now work, so I do need to scale each individual subtitle region. Any demo code


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