[mythtv-users] Transcoding

[Brian Wood]

On Sunday 30 November 2008 17:20:15 Paulin wrote:
> On Sun, Nov 30, 2008 at 6:11 PM, David Greaves <myth at dgreaves.com> wrote:
> > Paulin wrote:
> > > I've been recently playing around with transcoders and got something
> > > working for reformatting HD so my frontend can handle it.
> > >
> > > Now I'm curious if there is a way to have the transcoder run as the
> > > stream is read in.
> > >
> > > For example
> > >     Video card -> mpeg2 stream -> transcode -> write to file
> >
> > Unless you're transcoding more quickly than real-time then the backlog of
> > data
> > in the stream will need to go somewhere; typically to disk...
> >
> > David
>
> Let me try asking this again because I may not have explain it good.
>
> Right now it looks like when something records it finishes recording (60
> minutes later) then it runs the commercial flagging and then the
> transcoder. The transcoder takes as long as the program did (60minutes).  
> So I'm wondering if it is possible to run the transcoder as it records
> instead of after.  The comercial flagging I could hold on till the end for.
>
> Basically the reason I'm asking is currently my front end can not handle HD
> recordings.  So I would like ti to be read by the card, transcoded, saved
> to disk, then played on front end before the show end.
>
> Hopefully that make sense.

Yep, you want to transcode on the fly as you capture, then record.

Since you are going to watch in SD anyway,  most programs are broadcast in SD 
as well, could you just try and record that in the first place?

If not, I think there is a setup parameter that sets how often to scan for 
jobs (like transcode jobs). I think the default is 1 hour. If you can find 
that and shorten it up a bit, you could get the transcode job to start a lot 
sooner.

Transcoding puts a load on CPU and disk I/O. Depending on your hardware, you 
might nnot be able to handle watching, recording and transcoding at the same 
time. You could nice the transcode more, but of course this will slow it 
down.

If the source material is h264 I suspect you are asking too much of all but 
the fastest systems, but if it's MPEG2 you can probably get away with it. I'd 
worry about the disk I/O more than the CPU, unless it's h264.

-- 
beww
beww at beww.org