[MPlayer-users] Re: Which TV card ?
olli at secnetix.de
Wed Aug 20 18:48:45 CEST 2003
Tuukka Toivonen <tuukkat at ee.oulu.fi> wrote:
> On Wed, 20 Aug 2003, Oliver Fromme wrote:
> > You can record in uncompressed YUV format which is very
> > good quality. Requires 15 MBytes/sec. That way, you can
> > store about 3 hours on a 160 GB disk.
> Aren't you overestimating slightly? I remember getting something like 15.9
> MB/s, and that's only for audio+video (container format makes some overhead
> too). For 160 GB disk at 16 MB/s, it's only 2 hours 39 minutes.
I'm sorry, I should have been clearer.
I'm recording at DVD resolution which is 720 x 576 (for PAL).
Therefore: 720 x 576 x 1.5 x 25 / 1048576 = 14.83 MB/sec.
Plus audio (raw PCM at CD quality): 44100 x 2 x 2 / 1048576
= 0.17 MByte/sec. Together that's exactly 15 MByte/sec.
> Also, for uncompressed video, hard disk speed can be a bottleneck. I have
> an SCSI disk for which hdparm reports 50 MB/s which is much more than 16
> MB/s, but don't trust that. With reiserfs it nevertheless was not fast
> enough for recording video. Works fine with ext2, so don't use journaling.
I'm using UFS2. My Samsung 160GB disk has a sequential
write speed of about 45 MByte/sec at the beginning. I
haven't measured it towards the end, but it is certainly
still enough for video recording (at least 25 Mbyte/sec,
> I'm personally planning to buy 2*120 GB disk and configure it as RAID-0. It
> will be faster and cheaper than the equivalent space as a single disk [*].
That's true. I've opted for the 160 GB Samsung because
it's pretty cheap around here (100 Euro).
> [*] Why the heck hard disks with multiple platters don't use RAID
I don't think it would make much sense. RAID 1 or 5 (for
redundancy) is useless, because usually the whole drive
fails, not just one platter. And RAID 0 only makes sense
when the components can be accessed independently, which
is not the case within one drive, because there's only
one actuator for the drive heads, so you cannot move the
heads independently from each other. So, an operation on
platter 1 would still block an operation on platter 2.
Also ... The "D" in RAID stands for disks or drives.
If it was for platters, it would have to be called RAIP.
Oliver Fromme, secnetix GmbH & Co KG, Oettingenstr. 2, 80538 München
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and may not necessarily reflect the opinions of secnetix in any way.
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