[FFmpeg-devel] [PATCH] avcodec: add minimal teletext subtitle decoder

[Aman Gupta]

On Thu, Apr 26, 2018 at 8:12 AM, Nicolas George <george at nsup.org> wrote:

> Aman Gupta (2018-04-26):
> > Another reason I discounted libzvbi is because it seems unmaintained,
> > without a new release is over 5 years.
>
> Did the teletext standard evolve in the past five years?
>

I don't know, but there it is atleast one bug causing tests to fail on
macOS which has been unfixed for 4 years.

I managed to install libzvbi by hand and try it out. With `-txt_format
text`, the generated output text is the same but without positions/colors.
The ASS positioning code could be ported over, but it looks like
vbi_print_page_region() strips out all the color information so there
doesn't seem to be an obvious way to support text coloring.

The zvbi decoder also hardcodes a (configurable) 30s end time per subtitle,
which causes them to pile up on the screen and not disappear when they're
supposed to. The logic from my decoder could also probably be ported over,
under a new `-real_time 1` flag like I added to ccaption_dec last year.

Here's a side by side comparison:
https://dzwonsemrish7.cloudfront.net/items/2x1z3k0C0X3v0Z2j1F3b/teletext-sub-comparison.jpg

I agree it would be ideal to have only one teletext decoder that works for
everyone. However I'm done with my teletext project, and don't have time
right now to redo all that work in the zvbi encoder. I also live in an ATSC
region and don't use teletext myself, so I don't really care whether or not
my decoder is merged into ffmpeg. I only shared it because some people on
IRC expressed interest.

Aman


>
> Regards,
>
> --
>   Nicolas George
>
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