[FFmpeg-devel] [PATCH] avcodec/mpeg12dec: ignore scte20 captions when a53 data is also present

Aman Gupta ffmpeg at tmm1.net
Wed Mar 7 20:14:51 EET 2018

On Wed, Mar 7, 2018 at 9:49 AM Michael Niedermayer <michael at niedermayer.cc>

> On Tue, Mar 06, 2018 at 02:25:12PM -0800, Aman Gupta wrote:
> > From: Aman Gupta <aman at tmm1.net>
> >
> > Some streams include both a53 and scte20 data. Before this commit,
> > the scte20 data would be used instead of the a53 data.
> >
> > See https://s3.amazonaws.com/tmm1/ccaptions/scte20plusa53.ts,
> > which produced garbage captions since 3f1a540204a8c187f77b3805d.
> > ---
> >  libavcodec/mpeg12dec.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> why does the combination produce garbage ?

In my sample, the scte20 data by itself produces garbage captions. I'm not
sure why.

> why should not both be exported or it be user selectable?

>From what I've seen in US broadcast television, scte20 is only used on
standard-def content and everything else uses normal a53.

I'm not sure how we would export both since there's only one type of side

> also turning one off for ever seems problematic for concatenated
> sequences. not every sequence would need to contain both i guess

Yea that's theoreticaly possible, but I'd rather wait to add support until
someone actually sees it in the wild.

Before I added scte20 support a few months ago no one even noticed it was
missing. It doesn't seem to have wide spread use.


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