[FFmpeg-devel] (no subject)

Oliver Fromme oliver at fromme.com
Tue Jul 29 10:45:43 CEST 2014

Carl Eugen Hoyos wrote:
 > Oliver Fromme <oliver <at> fromme.com> writes:
 > > That's why I appreciate the patch very much
 > > that Carl Eugen has created.
 > Did you test the patch?
 > I think it will not get applied without a test.

Oh yes, I tested it, and it works!
Sorry, I thought I'd already mentioned it.

I've used the same file for testing that I used
when reporting the problem in the ffmpeg-users
list.  With your patch, the following works:

$ OPTS="-vn -an -map "#0x21" -scodec dvdsub test-subs.mkv"
$ ls -lh *.mpg
-rw-r--r--  1 olli  wheel   5.5G Jul 27 17:14 dumpstream.mpg
$ ffmpeg -analyzeduration 6000M -probesize 6000M -i dumpstream.mpg $OPTS

Input #0, mpeg, from 'dumpstream.mpg':
  Duration: 01:37:01.70, start: 0.287267, bitrate: 8115 kb/s
    Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p(tv), 720x576 [SAR 64:45 DAR 16:9], max. 9800 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x80]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s
    Stream #0:2[0x81]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s
    Stream #0:3[0x20]: Subtitle: dvd_subtitle
    Stream #0:4[0x21]: Subtitle: dvd_subtitle
Output #0, matroska, to 'test-subs.mkv':
    encoder         : Lavf55.50.100
    Stream #0:0: Subtitle: dvd_subtitle (dvdsub)
      encoder         : Lavc55.69.100 dvdsub
Stream mapping:
  Stream #0:4 -> #0:0 (dvd_subtitle (dvdsub) -> dvd_subtitle (dvdsub))
Press [q] to stop, [?] for help
size=       4kB time=00:00:17.56 bitrate=   2.1kbits/s    
video:0kB audio:0kB subtitle:4kB other streams:0kB global headers:0kB muxing overhead: 21.333687%

The first subtitle packet of the stream #0x21 is at 0:55:54
which is at an offset of about 3.4 GB into the file.

There's still the problem that the timestamps are wrong when
I extract the subtitles only (no video, no audio), but that
has nothing to do with your patch.  It's easy to work around
by just extracting one audio track along with the subtitles,
then discard the audio track if I don't need it.

 > [...]
 > > Maybe I'll try to make a patch that can do this
 > If you consider to invest time in DVD reading, 
 > please work on the dvdnav patch:
 > http://thread.gmane.org/gmane.comp.video.ffmpeg.devel/104257/focus=140297

That thread seems to center on DVD playback with ffplay,
including menu navigation.  I have to confess that that's
not what I have in mind; I have never used ffplay, and I
don't care about DVD menus.

My goal is to enable ffmpeg to be able read one title from
a DVD and encode it.  The number of the title will be given
on the command line, the default will be the longest title
on the DVD.  As a side effect, I assume that ffplay will be
able to play a title from a DVD in the same way.

Of course, if that's not what the ffmpeg project wants, I
have no problem with that.  I can just as well continue to
use separate tools for the job, and use ffmpeg only for the
actual transcoding.

By the way, some (or maybe even most) of the statements in
the post that you linked are wrong.  For example, the video
system (PAL, NTSC) never changes within one title.  It can
change from one VTS to another, but since you always encode
by title, changes in video system don't have to be taken
into account.  

I guess some of the wrong assumptions in the post come from
the bad habit to encode VOB files directly, but trying to
do that is a mistake and fails in many cases.  You *always*
have to use the information from the IFO files in order to
read a title properly, i.e. assemble the cells that belong
to this title's PGC in the right order.

Best regards

``We are all but compressed light'' (Albert Einstein)

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