Mailing List Archive: Frame Drops

Frame Drops

Nov 11, 2002, 3:27 PM

Post #1 of 3 (1494 views)

Hello,

I've been using a relatively simple PVR setup for the last year using Nuppelvideo, transcode and a few bash scripts which handle the distributed encoding over a few servers using NFS. I have one serious question before I take the plunge to mythtv:

How is mythtv offering realtime PVR functions (pause/rewind) with fairly reasonable quality (512h-640h) without dropping a huge number of frames?

My Nuppelvideo to transcode setup, produces 2 gig files every 15 minutes (640x480) which take nearly an hour to encode to divx5 or mpeg2 on a 935mhz P3. How does mythtv offer the same functions in realtime? Even with a quad Xeon 2ghz box, you couldnt transcode from nuv to mpeg/divx5 at 640x480 @ 23fps in realtime. Either I've been wasting the last year with serious problems in my setup, or mythtv needs to make its capabilities clear in the FAQ.

Either way, mythtv looks like a great package and I'm looking forward to integrating it with my current PVR setup.

PS: I can't code. But I can write a mean bash script ;)

Cheers,
Oatz

Re: Frame Drops [ In reply to ]

maillists at sonictech

Nov 11, 2002, 7:12 PM

Post #2 of 3 (1410 views)

Permalink

On Mon, Nov 11, 2002 at 05:27:32PM -0500, Oatz wrote:

> My Nuppelvideo to transcode setup, produces 2 gig files every 15
> minutes (640x480) which take nearly an hour to encode to divx5 or
> mpeg2 on a 935mhz P3. How does mythtv offer the same functions in
> realtime?

It mainly uses rtjpeg which is designed for real time compression (similar
to mjpeg?) If your machine isn't pretty darn fast though you'll probably
have to drop the capture resolution a bit.

> Even with a quad Xeon 2ghz box, you couldnt transcode from
> nuv to mpeg/divx5 at 640x480 @ 23fps in realtime.

I don't know if it's comparable but I can transcode (using mencoder) from
mjpeg to mpeg4 at around 20fps. This is on a dual 500Mhz Celeron system so
I guess a dual 1GHz P3 should handle this in real time. Going to a quad box
wouldn't speed it up much but would allow denoising (sp) or other effects in
real time as well. On my box converting to mpeg1 or mpeg 2 took a lot
longer (like 4-8x longer) but that was using a different encoder too. BTW
there isn't currently any way to convert from MythTVs modivied nupplevideo
to anything else but I'm sure someone will get to that eventually.

--
Ray

Re: Frame Drops [ In reply to ]

ijr at po

Nov 11, 2002, 7:58 PM

Post #3 of 3 (1444 views)

Permalink

On Monday 11 November 2002 05:27 pm, Oatz wrote:
> Hello,
>
> I've been using a relatively simple PVR setup for the last year using
> Nuppelvideo, transcode and a few bash scripts which handle the distributed
> encoding over a few servers using NFS. I have one serious question before I
> take the plunge to mythtv:
>
> How is mythtv offering realtime PVR functions (pause/rewind) with fairly
> reasonable quality (512h-640h) without dropping a huge number of frames?
>
> My Nuppelvideo to transcode setup, produces 2 gig files every 15
> minutes (640x480) which take nearly an hour to encode to divx5 or mpeg2 on
> a 935mhz P3. How does mythtv offer the same functions in realtime? Even
> with a quad Xeon 2ghz box, you couldnt transcode from nuv to mpeg/divx5 at
> 640x480 @ 23fps in realtime. Either I've been wasting the last year with
> serious problems in my setup, or mythtv needs to make its capabilities
> clear in the FAQ.
>
> Either way, mythtv looks like a great package and I'm looking forward
> to integrating it with my current PVR setup.
>
> PS: I can't code. But I can write a mean bash script ;)

Yeah, I guess it's just not possible that I'm encoding at 640x480 to mpeg4,
encoding audio to mp3, and playing all that back in real time with plenty of
cpu to spare on an XP 1800+... Anyway, I can _almost_ do two encodes and a
decode process at those same settings, there's just not quite enough CPU. =)

Isaac