[mythtv-users] PVR350 TVOUT

Michael T. Dean mtdean at thirdcontact.com
Tue Jan 19 08:22:05 UTC 2010

On 01/19/2010 03:05 AM, f-myth-users wrote:
>     > Date: Mon, 18 Jan 2010 19:39:28 -0500
>     > From: "Michael T. Dean"
>     > Correct.  But, really, the PVR-350 decoder is useless, as with even
>     > almost-modern hardware, decoding 9.6Mbps 480i60 or 576i60 MPEG-2 in
>     > software on a general-purpose CPU is trivial.
>     > OK, actually, "useless" isn't the right term.  The PVR-350 decoder
>     > hardware is an anachronism.  It's not 1999, anymore.  :)
> What about handling closed captions?
> My understanding is that the 350 can only pass embedded VBI CC using
> its mpeg decoder and not via the X framebuffer.  But the PVR's use a
> nonstandard VBI embedding, so while one can pass CC into the stream
> and back out to the TV that way, it's not clear to me at all how this
> would work if using a 350 FB or a normal video card---something has
> to take that nonstandard encoding and make it available for Myth's
> internal player, so it can superimpose the captions on the screen
> instead of the TV doing so from line 21 data.

Myth can decode and display captions from ivtv-recorded MPEG-2--thus the
lack of complaints from people who have PVR-250's and PVR-150's and
PVR-500's and no PVR-350's.

> What's the toolchain here?  Is it automatic, or do people have to set
> up user jobs to run cc-srt (or whatever) over the stream?  Does it
> work in LiveTV as well?  (LiveTV CC seems to imply a toolchain that
> can do continuous conversion on the file being generated, or native
> understanding in Myth's internal player of PVR-style VBI CC embedding;

We have the latter.

> I don't know if that exists sans 350 support.  The last time I tried
> to research this topic, I found too many suspiciously ancient and
> contradictory sources.)
> In other words, you've said many times that you regretted buying your
> 350, but for SDTV people, it serves a very definite need and one that
> has some unique features---and not just CC either; witness WSS in PAL/
> SECAM, etc.  Being able to have built-in alternatives for those needs
> that are as painless as using the 350 seems important if you're going
> to dismiss the 350 as "useless"; can you explain how to get equivalent
> functionality?  This is something that many people decommissioning
> 350's will need to know, and the whole story isn't immediately obvious
> to me.

As always, anyone wanting WSS support can add it to Myth.  Until then,
people can use Adjust Fill or even Manual Zoom Mode to get the
functionality.  In all these years, though, we've never had anyone who
felt adding WSS support was worthwhile.  :)  (And, as analog TV becomes
less and less common, I seriously doubt anyone will get that motivated
to add new analog-only features to Myth.)

And, as mentioned, we already have caption support.  Myth takes the
approach of handling all the video needs for the user and not relying on
the TV or output device.

> [I hate to keep hammering on this issue, but for some people, lacking
> CC support means they might as well not bother trying to watch TV at
> all.  Like many accessibility issues, it often seems trivial to those
> who don't need it and often ignored, but is absolutely essential to a
> small population.]

I haven't watched a TV show (on my TV, at least) without captions
enabled since shortly after I started using Myth--and I used PVR-x50's
with nvidia video cards for several of those years and have always had
Myth decoding the captions and never used my TV to decode them.  Believe
me, I will be the last Myth user to forget about captions.


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