Re: [FFmpeg-devel] [PATCH 2/2] avcodec/libzvbi-teletextdec: formatted ass output

Mon, 07 May 2018 16:08:08 -0700 


On Mon, 7 May 2018, Aman Gupta wrote:




On Mon, May 7, 2018 at 12:50 PM, Aman Gupta <ffm...@tmm1.net> wrote:


      On Sun, May 6, 2018 at 2:05 PM, Marton Balint <c...@passwd.hu> wrote:
            Inspired by the VideoLAN text decoder and its port to FFmpeg made 
by Aman
            Gupta.


Thanks for incorporating my changes.

I ran some tests, and colors work as expected. Positioning also works well, and 
is also pretty close to my version.


I found that some live streams are not chopping empty lines correctly. I see 
extra newlines at the end:

  Dialogue: 
0,0:13:21.66,9:59:59.99,Default,,0,0,0,,{\an1}Simson,\hPeter\hHartcher,\hRobyn\hParker
 \Nand\hBenjamin \N \N \N

Here's a sample which shows extra newlines: 
https://s3.amazonaws.com/tmm1/teletext/capture_live1.mpg



This is kind of intentional, in this case the new lines are kept to 
position the subtitles a bit higher, and not to the very bottom of the 
screen, to keep the rough position of the teletext subtitles. At first I 
used \pos as well, but it only worked once per line for me, so I had to 
use some kind of newline-positioning anyway, and using native vertical 
alignment instead of \pos seemed nicer. (E.g. it allows the user to change 
left/right alignment text margins more easily in the headers or by 
an override).




It also looks like the "erase page" command is not being processed, which 
causes stale captions to stay on the screen in some cases.
This is especially confusing when part of an old caption remains on one line, 
but then newer captions appear on another line.

Here's a sample that shows lines not being cleared correctly: 
https://s3.amazonaws.com/tmm1/teletext/simple.mpg


With this sample, for instance, my decoder produces:

Dialogue: 
0,0:00:01.90,9:59:59.99,Default,,0,0,0,,{\an8}{\pos(192,213)}{\c&HFFFFFF&}and 
this, as you rightly say,\N
Dialogue: 0,0:00:01.94,9:59:59.99,Default,,0,0,0,,{\an8}{\pos(192,213)}{\c&HFFFFFF&}and 
this, as you rightly say,\N{\an8}{\pos(192,231)}        {\c&HFFFFFF&}is American.\N
Dialogue: 0,0:00:04.86,9:59:59.99,Default,,0,0,0,,
Dialogue: 
0,0:00:04.94,9:59:59.99,Default,,0,0,0,,{\an8}{\pos(192,231)}{\c&HFFFFFF&}It's 
rather nicely made.\N
Dialogue: 0,0:00:06.62,9:59:59.99,Default,,0,0,0,,
Dialogue: 
0,0:00:06.70,9:59:59.99,Default,,0,0,0,,{\an8}{\pos(192,213)}{\c&HFFFFFF&}It's 
got this fabulous\N
Dialogue: 
0,0:00:06.74,9:59:59.99,Default,,0,0,0,,{\an8}{\pos(192,213)}{\c&HFFFFFF&}It's got this 
fabulous\N{\an8}{\pos(192,231)}   {\c&HFFFFFF&}cast finial here\N
Dialogue: 0,0:00:10.34,9:59:59.99,Default,,0,0,0,,
Dialogue: 
0,0:00:10.42,9:59:59.99,Default,,0,0,0,,{\an8}{\pos(192,213)}{\c&HFFFFFF&}of a 
very muscular figure\N
Dialogue: 0,0:00:10.46,9:59:59.99,Default,,0,0,0,,{\an8}{\pos(192,213)}{\c&HFFFFFF&}of 
a very muscular figure\N{\an8}{\pos(192,231)} {\c&HFFFFFF&}pulling this medallion.\N
Dialogue: 0,0:00:15.50,9:59:59.99,Default,,0,0,0,,
Dialogue: 
0,0:00:15.58,9:59:59.99,Default,,0,0,0,,{\an8}{\pos(192,213)}{\c&HFFFFFF&}So 
it's got strength to it. It's a\N
Dialogue: 0,0:00:15.62,9:59:59.99,Default,,0,0,0,,{\an8}{\pos(192,213)} {\c&HFFFFFF&}So 
it's got strength to it. It's a\N{\an8}{\pos(192,231)}{\c&HFFFFFF&}really characterful 
piece of silver.\N
Dialogue: 0,0:00:19.14,9:59:59.99,Default,,0,0,0,,

And the decoder in this patch produces:

Dialogue: 
0,0:00:02.02,9:59:59.99,Default,,0,0,0,,{\an2}and\hthis,\has\hyou\hrightly\hsay,
 \Nis\hAmerican. \N
Dialogue: 
0,0:00:05.02,9:59:59.99,Default,,0,0,0,,{\an2}and\hthis,\has\hyou\hrightly\hsay,
 \NIt's\hrather\hnicely\hmade. \N
Dialogue: 
0,0:00:06.82,9:59:59.99,Default,,0,0,0,,{\an2}It's\hgot\hthis\hfabulous 
\Ncast\hfinial\hhere \N
Dialogue: 
0,0:00:10.54,9:59:59.99,Default,,0,0,0,,{\an2}of\ha\hvery\hmuscular\hfigure 
\Npulling\hthis\hmedallion. \N
Dialogue: 
0,0:00:15.70,9:59:59.99,Default,,0,0,0,,{\an2}So\hit's\hgot\hstrength\hto\hit.\hIt's\ha
 \Nreally\hcharacterful\hpiece\hof\hsilver. \N
Dialogue: 
0,0:00:19.30,9:59:59.99,Default,,0,0,0,,{\an2}So\hit's\hgot\hstrength\hto\hit.\hIt's\ha
 \NBut\hmost\himportant\hof\hall, \N

At the ~5s mark, the text on the screen should say "It's rather nicely made", but this 
decoder still displays the line "and this as you rightly say" from the previous sentence.



The mix of different subtitles showing up seems like a libzvbi bug :( ... 
I will try to send a patch to sourceforge hoping it will get picked up and 
integrated to a future release...



Also there is a slight difference in how empty subtitles are forwarded. 
For empty subtitles I always used AVSubtitleRect type AVSUBTITLE_NONE, you 
used AVSUBTITLE_ASS. I prefer AVSUBTITLE_NONE, because with it
ffmpeg -fix_sub_duration creates a valid ass file without empty 
subtitles.



I also have several other samples which use various features, available at the 
same URL:

capture_formatting1.mpg
capture_formatting2.mpg
capture_formatting3.mpg
capture_live1.mpg
capture_live2.mpg
capture_notCaptionedMessage.mpg
capture_threeLines1.mpg
capture_threeLines2.mpg
capture_threeLines3.mpg
capture_threeLines4.mpg
capture_yOffset1.mpg
three.ts
four.ts


I will have a look at those, thanks for your feedback.

Regards,
Marton
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