On Sunday 08 June 2008 02:32:55 Joe Trivers wrote:
> Hi all,
>
> I have been using ivtv with MythTV and two Adaptec VideOh PCI cards
> happily for several years. Recently I upgraded from kernel 2.6.17
> with ivtv 0.7.0 to kernel 2.6.24 with ivtv 1.0.3. After upgrading
> (no change to MythTV), closed captions in new recordings and in live
> tv were missing many characters. Earlier recordings played back
> fine. I have since found a solution, but I wanted to ask about it.
>
> Captions were missing character pairs, averaging maybe two or three
> pairs of adjacent characters per line of caption text. For example,
> a caption might read "WHERE NOAN HAS GONE BEFE." dropping pairs
> "space, M" from NO MAN and "O,R" from BEFORE. That's an actual
> example from the Andromeda Strain broadcast on A&E last week.
> Sometimes it seems to drop newline characters so a two-line caption
> appears on one line and runs off the side of the screen. It's not
> unwatchable, but it's a major nuisance. My hearing isn't very good,
> and I can't always follow the dialog without captions, even with the
> volume turned way up.
>
> I only found one mention of a similar problem on the lists, at
> http://www.gossamer-threads.com/lists/ivtv/users/36922#36922
> and that one doesn't appear to have been resolved.
>
> I upgraded again to kernel linux-2.6.24-gentoo-r8 (from r3) and
> upgraded to MythTV 0.21 using the tarball from the web site, but
> nothing helped. My system is an IBM NetVista Pentium 4 at 2GHz
> running Gentoo Linux with an old nVidia Vanta graphics card and the
> nvidia driver. I'm in Canada (Toronto) so my cable signal is NTSC.
> The TV cards both show in lspci as:
> Multimedia video controller: Internext Compression Inc iTVC16
> (CX23416) MPEG-2 Encoder (rev 01)
>
> Today I was looking at the source and noticed that function
> ivtv_vbi_setup in ivtv-streams.c had been changed to use a ringbuffer
> size of 8 for sliced vbi, where in the older version that worked for
> me it used 2880/vbi_sliced_size or about 45. It appears the change
> was made in trac changeset 3488 on 24 October 2006. I tried
> increasing 8 to 16 and rebuilt my kernel, and now my captions are
> perfect again.
>
> Has anyone else had this problem? Does anyone know of a better fix,
> or of any undesirable consequences of the change I made?
I'll have to try this myself. It's a very interesting observation. I
still want to have the VBI stuff fixed, but I need a full day of work
to properly test it all, but it seems that each weekend I have
something else that's preventing me from finishing this. It's on the
top of my TODO list, though.
Regards,
Hans
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