How to add subtitles as a DVB stream (not burnt into the video)

[martinu]

I have an MP4 (H264/AAC) video file and a SRT file of subtitles. I can play the video and if I do Subtitle | Add a subtitle file and give the SRT filename, the subtitles are displayed. So the input files are OK.

I want to add the subtitles to a copy of the file so they are an additional DVB subtitle stream alongside the video and audio - the same as I'd get with an off-air recording. I don't want to burn the subtitles into the video stream (although I've made that work OK).

But try as I might, the output file still only has the same video and audio stream as the input, with no addition DVB subtitle stream.

This is what I'm doing:

Media | Stream

Add the video file (an MP4 file)
Check "Use a subtitle file" and browse for it.

Stream button, down-arrow to select "Convert"

Fill in the name of the output file
Edit the profile (a copy of the "Video - H264+MP3 (MP4)" profile with options:

Encapsulation MP4/MOV (and under "Features" it does list Subtitles!)
Video: Codec=H-264, Bitrate/Quality=not used, frame rate=same as source, custom options=[blank]
Audio: Keep original audio track (no need to transcode it)
Subtitles: Codec=DVB subtitle, Overlay subtitles=not checked (*)
Save
Start

A file is produced but it does not contain the additional DVB subtitles stream (as shown in Tools | Codec Information) and it is not selectable in the Subtitles | Sub track menu.


(*) If at this stage I check "Overlay subtitles", the subtitles are burned into the video, so that aspect works - but I want a separate stream so the user can choose to display or not display them.



So what am I doing wrong? All the tutorials I can find online talk about burning in the subtitles. I can't find any which walk me through the process of adding the subtitles as a DVB stream.

[InTheWings]

We don't encode to DVB which is bitmap

[martinu]

Ah! So why is there an option "DVB subtitle" (as an alternative to T.140) on the Subtitle | Codec control of the profile? I thought this was where I chose the format of subtitles I wanted to add to the output file.

I naively thought that if VLC could render text into pixels for displaying over playing video or for burning into the output video stream, it would use the same code for rendering to the bitmaps needed for DVB subtitles.

Do I need an external program to render the subtitles to a bitmap file format which VLC then accepts on the Media | Stream dialog? If so, what format do I need to generate for VLC to be able to use it and what is a good (free) program to use?

Maybe this is a new feature request: for VLC to do the whoel job itself and to render text to bitmap using the same code as for burning into the video stream.