pantau:David,i've just checked the Avid Help again on HD Resolutions etc.; it says (as you also said as far as I remember) that 1080i/50 HDV is 1440 x 1080, as is DNxHD-TR 120.1080i/50 is 1920 x 1080, as is DNxHD 185 and DNxHD 120My question is: what do I really gain if I transcode HDV to DNX185 instead of DNxHD-TR 120, would that not mean that the 1440 pixels are simply interpolated to 1920, and therefore no real gain in quality??What is the difference between DNxHD-TR 120 and DNxHD 120, apart from horizontal resolution?And, as you were just talking about PCMCIA-Adapters for "serious" notebooks (I'm not saying mine is serious...), is a eSata-Adapter faster than a Firewire 800 one? In terms of throughput (185Mb/sec for DNX185 = 23MB/sec) I do not really understand the problem, even USB should be able to do this, no?Cheers, maybe you should think of compiling a book out of your forum contributions...Peter
doxilia:When you transcode HDV2 (1440h pixels) to DNX (1920h pixels) the process "reshapes" the pixels from anamorphic 1.33 to square 1.0. The pixels are not "interpolated" per se. As far as the "quality gain", it has more to do with the kind of signal that DNX media contains. It's a bit like converting raw onions (HDV) into French onion soup (DNX); the latter tastes alot better.
doxilia:Your observation about USB bandwidth is fine but also ideal. Bench a USB2 drive and you'll see that you'll get varying figures between 30 and 45 MB/s. For just playing back a single stream of continuous DNX 185 it "sort of" works. But NLE's, call media from all over the hard drive in rapid succession and also often dissolve between one stream and another. Sometimes you're requesting 3, 4 or more concurrent streams. Issues like drive latency (response time) come into play in these scenarios. This should provide some insight into how quickly your USB bandwidth maxes out and the interface bogs down. This is why the AV application world is flooded with high performance disk arrays. Other threads discuss arrays in some detail with specific reference to eSATA.
doxilia:thanks for the compliment (I assume I'm to take it that way.)
"Cheers, maybe you should think of compiling a book out of your forum contributions...Peter"
This comes close...
http://www.avid.com/resources/whitepapers/hdworkflowWP3.pdf?featureID=886&marketID=
berga:Just for the record about Mojo.Mojo does not need the bandwith of firewire or the PCI-card (which is there Mojo put the requirement, I need its own PCI-bus segment).The problem is this. If two PCI-cards share the same PCI-segment, they can not use it at the same time. If card one use it, it is not available for card two. You can think that the second card got a red trafic light.Mojo need green light everytime, because a delay of 2ms will miss one field and the playback is worthless, especialy if You need to play back to tape.(Credits for the trafic ligth example: Dom Q. Silverio).
pantau:I'm starting to catch up, but to be honest I don't really believe into "reshaped" pixels, at least not as much as in french onion soup. An uncoded HDV2 frame is 1440x1080, if I want to transcode it to DNX, I'll need 1920x1080, right? I do not see any other possibility to get there apart form interpolation. At the end, if we are talking about pixels, there is no anamorphic or square to me, just a pixel. Anamorphic or square is something which comes in at the display stage, squeezing the pixels (or not) on the monitor, TV-set etc., or am I wrong?So in terms of information (real, not interpolated resolution) I would say it should be o.k. if I finish editing on TR DNX 120 on my laptop, and let the guys from TV then transcode this to whatever format they like, to put it out on digibeta?Peter
doxilia:In the end, your transcoding to DNX TR for laptop editing keeps things a little lighter than going with regular DNX; this helps. However, if the TV folks are transcoding your DNX TR to "whatever they like", your images will, in a sense, go through TWO codec cycles, rendering your programs third generation. If the TV station is mastering HDCAM or DigiBeta from your HDV footage and they are using Avid, there's a good chance that they wouldn't alter your footage codec further than your first DNX full raster pass. But there's always a chance that they may put it into another codec if they are just going out to DBeta.
Cameras don't lie yet liars may use cameras
pantau:Hi David,thanks again, I surrender... I'll transcode it all to DNX185 and get a decent harddisk...By the way, Berga in an other thread was explaining me why I should render DV50 instead of DV25; how would this be in the HD-world? What format should one render in a DNX185 project? 1:1? That would mean huge files...
doxilia:Mojo aside, current SATA has a spec transfer rate of 300 MB/s while FW400 has 50 MB/s, FW800 has 100 MB/s and USB2 has 60 MB/s. In practice FW400 is often faster than USB2 (for unimportant reasons). FW800 implementations are not all equal and some are not up to snuff. In general, it performs better than FW400. On the other hand, SATA is the most common native hard drive interface presently. It provides the fastest transfer rate with the least arbitration compared to FW and USB. Further, external SATA is as easy and practical to use as USB or FW.
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