[was: New ATSC messages]

On 18 Dec 2007, Nico Sabbi wrote:

> Il Tuesday 18 December 2007 03:25:27 Bill Pringlemeir ha scritto:

>> I have been using atscap to capture the streams.  It seems that
>> mplayer plays the "ts" stream much better than the direct V4L2
>> stream. I think that this is due to the fact that the file provides
>> a huge buffer.  Is there a FAQ entry somewhere on the preferred
>> method to capture streams?  I imagine it is 'cat'ing some device.

> you can also try to use some -cache 4096 with -speed 0.97 -af 
> scaletempo -mc 10

I had tried both the speed, tempo and mc adjustments.  I didn't know
that cache would do the same thing (only in memory) as using atscap to
store the stream.

>> I know the XvMC will work, but is it correct that an
>> external card will reduce the FSB memory pressure?  None of the
>> HDTV faqs I have read seemed to mention anything of this.

> if you send a lower resolution image.
> -vc ffmpeg12 -lavcopts lowres=1 will have a significant speedup

Thanks, this works great.

>> The i810 driver (now intel) supports many chipsets, but very few
>> have XvMC support.

> try with intel drivers

The intel drivers are much the same.  They might support XvMC with
newer i9xx chips, but only the i810-830? are supported.  None of the
intermediate chipsets have XvMC available.  I also think that using
system SDRAM is also a big performance hit to the front side that many
systems can not handle.

>> It did seem that the libmpeg2 might be able to do a crude scaling
>> at the start of the decode.  Ie, use the frequency information to
>> do a nice integer scale that would reduce the memory bw.

> I don't have any knowledge of the decoding process, better ask
> ffmpeg-devel where optimizations are generally discussed

It seems that the "-lavcopts lowres=1" option does this (maybe not in
the manner I described).  The only advantage of my method above is
that rational scaling factors could be used, but it might be
exceedingly complex as the mpeg decode and scaling would take place in
the same step.

Anyways, the "-cache" and "lowres" enable ATSC viewing that is better
than any NTSC signals with my system.  (Obviously the resolution is
better, but the play back is smooth without stutter with the exception
of signal noise).

Thanks again,
Bill Pringlemeir.