Re: Video subtitles

[Gábor Boskovits]

Hello,

Ricardo Wurmus <address@hidden> ezt írta (időpont: 2018. dec. 20.,
Cs, 9:26):
>
>
> Hi Laura,
>
> > The first question I need to answer is if subtitles are going to be
> > present all the time as part of the video, or they should be able to
> > be disabled. We had that discussion somewhere, but if they are going
> > to be present as part of the video (hardsubs) only .srt and .ass - the
> > ones created by default by aegisub - are supported by ffmpeg:
> > https://trac.ffmpeg.org/wiki/HowToBurnSubtitlesIntoVideo
>
> The subtitles should be provided as a separate file, so that they can
> easily be swapped out or disabled.  Some container formats allow
> embedding the subtitles, but we would need to embed all subtitles in all
> language variants of all video files, and this seems like more work.
> Having the subtitles as separate files is more convenient for
> processing.
>

Yes, and the embeding into the container can be automated at the end if needed.

> > I remembered how much time each audio file lasted, so I added one
> > subtitle for each svg file that appears in the video - they were just
> > three- with the full content of what is said in the audio.
>
> It is more common to have a single subtitle file per video.

It would be ok to have a single subtitle file.

>
> > The drawback of this is that each svg file in the video has the full
> > subtitle text before the speaker mentions those words - I will ask
> > Björn tomorrow to upload it to their IPFS so that you can see what I
> > mean.
>
> You can time the appearance of text.  I’ve only ever written srt
> subtitle files by hand before, but they are all similar in that they
> associate a piece of text with a timestamp.  The text is then displayed
> at the specified time only.
>
> You can figure out the appropriate timestamps by playing back the video
> and recording the times when something is said that should be titled.
>

So to make this more explicit, you could break down the text to smaller
chunks, then time the appearance of those.

> > When choosing the format of the subtitles, Ricardo mentioned that it
> > was better using usf because it had support for styling. The good news
> > is that aegisub allows us to do so in their own interface, but  in
> > their .ass format, one of the two that supports ffmpeg,  which is not
> > compatible,  I guess, with the formats mentioned in po4a for
> > translation. However the .ass subtitle can be exported as .ttxt -
> > which is an XML, and that can be converted back to .ass.
>
> “.ass” files are very popular and very rich in styling features.  “.usf”
> files are less commonly seen in the wild.
>
> I have no strong opinions about using “.usf”.  “.ass” may just be fine.
> Apparently, it can be converted to po files for translation with
> “sub2po”, which is part of the “translate” toolkit.  I have no
> experience with this, and I think it would be better to use a format
> that didn’t require even more tools to work with.
>
> This shouldn’t block you, though.  It is fine to use Aegisub manually to
> create the initial subtitle and then convert it to another format.
> Aegisub does not need to be part of the automated process to compile the
> videos.
>
> --
> Ricardo
>
>

I believe that we don't want to do anything fancy with the subtitles, so I
guess any format would be just fine, provided we have tool support.

Best regards,
g_bor