glitches, another story *g*

[Marcus O.C. Metzler <mocm@netcologne.de>]

Thomas Jagoditsch writes:
 > hi all.
 > 
 > after switching to a bx-board with an old ´350 and 128megs of ram 
 > (yeah, its a bit "overdressed", but the parts were there anyway 
 > except the casing and the memory [they got the 128 only, no 64 
 > *grrr*]) i´ve got error-free recording without any problems and no 
 > syslog-messages, hoooray ;-)
 > 
 > but (there allways seem to be a "but") i have to report another 
 > strange thing.
 > 
 > playing around with the machine on the weekend i recorded the 
 > qualifying of the motorbike-gp on eurosport while watching it.
 > at the commercials i made a switch to the syslog-console (found a 
 > riva-tnt with video-out which works per default on the tv when there 
 > is no vga-screen connected) to look for recording errors. there were 
 > none.
 > 
 > trying to playback of some interesting scenes i discovered that in 
 > playback-mode the recording sometimes lost a couple of frames (the 
 > bikes were REAL FAST this moments *g*), then lost audio for a couple 
 > of sedonds to minutes with good picture, again good audio with lost 
 > frames and so on.
 > 
 > checking the syslog showed no errors so i became curious.
 > 
 > playing back the same scene a couple of times showed that losing 
 > frames or audio _didnt_ happen the same time every playback.
 > some runs i´ve got perfect audio, next run no audio at all (beside 
 > the in-sync glitches that every playback has) - this leads to the 
 > conclusion that the recording itself is ok (am i right ?!?) but 
 > playback has problems.
 > 
 > trying to crosscheck on other channels showed no problems at all.
 > recording the end of "men in black" on pro7 yesterday and playback of 
 > this 20-minute recording behave correctly with no glitches at all.

Thanks, for the report, I think that confirms our suspicion that the
interleave of auduo and video packages is sometimes not advantageous
for the internal buffers of the mpeg decoder. I guess that the video
bitrate and the size of the PES we write gets to large when you have
those fast scence in the motorcycle race. In order to fix that, we
will have to do some work, so please be patient. Another problem is
that it is hard to check. So if we think we have a solution, we will
check it into the CVS and tell you to test it vigorously :).

 > 
 > technical questions:
 > 
 > PAL/NTSC etc.:
 > my first (now thrown-out) thought was about the possible source of 
 > the video-signal. the gp happend in brasil, so maybe (the picture 
 > showes real bad colors and sharpness) they´re using ntsc to record 
 > and there is a kind of convert-process involved that could cause 
 > problems for the dvb.
 > recording of other events or even commercials on eurosport showed the 
 > same misbehaving, so this is out.
 > but, basicly, what about pal, ntsc ... is this important in the "new 
 > digital satellite world" ?
 >
 
Well, there is a difference between PAL and NTSC MPEG2, but the dvb
card can playback both. The only problem is that it can only playback
PAL as PAL and NTSC as NTSC (no PAL60 conversion at the moment). So
you need a TV that can display NTSC and PAL in order to be able to
view both. On the computer screen it makes no difference.

 > recordings/files:
 > is there any (non-programmer) way to find out more about the 
 > properties/specialities of the distict recordings, to help debuging 
 > the cause ? are there different sub-formats or are they identic 
 > despite the data ?
 > could i convert the recording to a mpg-file suitable to play on a 
 > windoze-machines media-player to cross-check the recording itself ?

The output of the driver (if you don`t use outstream=0 (which means
av_pes)) is on default a program stream (PS), which you should be able to
play back on any MPEG2 player (I hope). If you have an av_pes file you
can use av_pes2ps to convert it to a program stream ("av_pes2ps
<filename>"). You get av_pes2ps when you compile the program in the
av_pes2any directory and then "make links". You can also pipe directly
into the program, e.g. "cat /dev/video | av_pes2ps > myfile".

 > 
 > a lot of questions, i know *g*
 > btw: links to basics are welcome, too.
 > 
 > wbr.tja...
 > 
No problem. 

Marcus

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Dr. Marcus Metzler                             
mocm@netcologne.de                     http://www.metzlerbros.de
mocm@convergence.de                    http://www.convergence.de

Convergence Integrated Media GmbH          
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D-10178 Berlin                             
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