[MPlayer-users] About TV/VCR capture quality

[Gerog Veiz]

I use mencoder to
capture and the
quality is very
good. BUT: Even if I
only watch TV on my
monitor (direct
without recoding) I
can see compression
artefacts in many
broadcasts. Other
broadcasts are very
good. TV-Stations
seem to use poor
compression in some
places. There is no
way to remove them.
So be carefull if
you rate your
records. Make
records from several
stations. 
Here is the main
part of my recording
script. It also
includes audio
setup. I do not use
the audio record
feature of my
tv-card since if can
only do 32kHz.
'channel' is another
script which takes a
station abbrevation
and returns its
frequency. My files
are usually 4-6GB in
size and I can
seek(odml). But I
can not remove the
commercials without
reencoding currently
(avidemux).

 # set up audio
mixer
amixer cset numid=27
4,4 1> /dev/null	#
capture from line-in
amixer cset numid=28
on 1> /dev/null	#
capture on
amixer cset numid=29
0,0 1> /dev/null	#
capture volume: 0
(mininum) gives low
noise and avoids
oversteering
amixer cset numid=40
off 1> /dev/null	#
disable spdif
capturing (makes it
impossible to
capture from other
sources)
# start capturing
nice -n -10 \
mencoder tv:// -tv \
driver=v4l2:device=/dev/video0:normid=0:input=0:freq=$(/mnt/archiv/tvrec/channel
"$1"):fps=25:width=720:height=576:alsa:adevice=hw.0,0
\
-oac mp3lame
-lameopts cbr:br=128
\
-ovc lavc -lavcopts
vcodec=mpeg4:vbitrate=5000:keyint=125:mbd=2
\
-endpos $2:$3:00 -o
"/mnt/av/$4.avi" \
2>/mnt/archiv/tvrec/reclog.txt
1>/dev/null



-------
Ursprüngliche
Nachricht ------- 
Von:  Fabio S. 
<fast at ferrara.linux.it> 
Datum: Wed, 19 May
2004 11:53:31 +0200
(CEST) 
Betreff:
[MPlayer-users]
About TV/VCR capture
quality 


Well, now that
everything is well
configured, I am
making many
capturing tests,
trying settings
suggested in various
posts I found using
google and I have
some question which
didn't find an
answer on the
documentation.

1) If I capture raw
audio/video

mencoder -oac pcm
-ovc rawrgb -tv
driver=v4l2:width=384:height=288
-o
test.avi tv://

then when I look at
"mplayer test.avi"
the video is flipped
upside down.
Is this an error? I
realized that if I
then compress
test.avi the
compressed file is
flipped again and it
looks correct, so I
am thinking
that this is a raw
encoding "feature",
in some sense.

2) If my
computations are
right, with these
settings I should
expect to
use
384*288*3*25=8294400
bytes per second of
capturing, only for
video.
That is, about 29Gb
per hour... :-((

Now for compressed
encoding. The
command is:

mencoder -oac
mp3lame -lameopts
cbr:br=196
-ovc lavc -lavcopts
vcodec=mpeg4:vhq:v4mv:vbitrate=1200
-tv
driver=v4l2:width=384:height=288
-o test.avi tv://

This works fine:
capturing is smooth,
no frames dropped,
perfect
audio/video
synchronization,
correct frame rate
(25 fps).
The problem is that
I can see too much
"compression
artifacts"
(square blocks).
3) How to improve?
The bitrate seems
already quite high
and augmenting it
doesn't help.
4) Even if capturing
looks correct from
the messages, as I
said, when
playing back
test.avi the audio
looks a bit
distorted, in the
sense that
the quality is good,
but it seems that it
is played at a (very
slight) faster rate
than it should,
making  voices a
little bit different
from the original
(sorry, I can't
explain it better in
my poor english)
5) Trying to improve
video quality, I
added the "trell"
option, as
suggested on the
documentation but
capturing gets
worse: frame rate
slows
down to 15 fps.
6) I guess that when
compressing "on the
fly" while capturing
I can't do
a 2-pass encoding,
right?
7) Can someone who
makes captures and
is satisfied with
the results post
his settings?

(the hardware I use
is a 1.2GHz athlon,
521Mb RAM)

TIA

Fabio

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