How much does MPEG capture of analog loose???

klaatu2 wrote on 7/7/2003, 2:20 PM

Compared to AVI. I can do either, but like the smaller MPEG file size. If captured to MPEG through Dazzle, then later converted to DVI for editing to MPEG for playable DVD, have I lost much compared to the AVI capture?? Is the space worth any loss of quality?

Comments

Chienworks wrote on 7/7/2003, 2:40 PM

That's an extremely subjective question. My gut response is to say "Yes, you lose a lot!" and "No, saving space isn't worth it." But that's because i want the quality and have the space to use.

You also haven't specified what bitrate you plan on using for captures, but in general MPEG contains less data than DV AVI and therefore has more loss of information. If you could capture MPEG at 30Mbps then it would probably look as good as or even a bit better than DV AVI. The file size would also be the same so you wouldn't save on space.

If you're not doing any editing or re-rendering then capturing in MPEG in the same bitrate and format you want for the DVD then this would be a good way to go. However, even if you intend to do no editing, the chances that the DVD burning software you use will be perfectly happy with the file you capture from Dazzle will be slim and the file will probably be re-encoded anyway. Encoding from DV AVI to MPEG isn't too bad; Encoding from MPEG to MPEG can be a lot worse.

If you plan on doing any editing at all then capturing in AVI will not only be better quality, but the ease and speed of the editing process will be much greater.

klaatu2 wrote on 7/7/2003, 3:41 PM

Thanks so much for your answer.

By the way, you mention that MPEG at 30Mbps might look a bit better than DV AVI. Why? Isn't AVI uncompressed so all info remains?

swampler wrote on 7/7/2003, 6:03 PM

Not exactly. DV AVI is compressed at a 5:1 ratio. However, that is the compression the camcorder records at, so copying from camera to computer and back does not introduce any additional loss like MPEG does.

Chienworks wrote on 7/7/2003, 7:36 PM

DV is sampled 4:1:1 which means that strong colors can be slightly blocky. As far as a i know, MPEG doesn't suffer this particular limitation (at least i've never seen it mentioned).

Uncompressed AVI can be up in the 237Mbps range, so it contains substantially more bits than DV AVI.

Hmmm. Puzzling. 237Mbps for uncompressed, 30Mbps for DV. That's a ratio of almost 8:1. Hmmmm. So why is DV considered a 5:1 compression? Is that ratio calculated after the 4:1:1 sampling is applied? Curious.

TheHappyFriar wrote on 7/7/2003, 11:22 PM

When I was setting up a Vegas editing system for a sister TV station, we decided to use the ATI All in Wonder 7500 and captured compressed MPEG-2's. At about 10 mbps it looks as good as DV (to me). That make 40 second files that were aboput 40mb. When I capture DV on the Premiere/RT2500 system I use at work, the files are about 140mb. The files look the same when I compared them side by side. On top of that, the RT2500 mpeg 2 i frame capture SUCKS. it looks like 3mbs mpeg 1!

So, I found that the compressed mpeg 2's with the ATI looked as good (as i could tell) as the DV files I captured. But, since the mpeg's need to be decompressed a lot, vegas worked slower. It was an ok tradeoff for what the station needed to do.

farss wrote on 7/8/2003, 5:39 AM

The quality of MPEG has two components, spatial and temporal. From what I know of the process both are dependant on the bit rate however for a given bitrate the temporal resolution is also effected by the quality of the encoder and how much time it spends on the job.
If you don't think MPEG is capable of high res remember HD transmission is MPEG encoded, DVD is MPEG and at a maximum of 9 MBits/sec, a much better result than can be achieved with DV. The gotch in all this is real time encoding, until recently decent realtime MPEG encoding involved very expensive hardware whereas DV codec chips were much cheaper.

This situation is rapidly changing but it still doesn't make MPEG easy to edit!

riredale wrote on 7/8/2003, 6:01 AM

Compressions ratios are completely dependent on what you mean by "uncompressed" raw video. Regardless, the DV compression method has been shown for years to be a very powerful and almost completely transparent means of substantially reducing the video bitrate (it does nothing for audio). There are websites that spend many pages showing raw versus compressed images, and on a relative ranking, DV comes out slightly better than BetacamSP, which is a format used by a great many TV stations.

The general idea is to shoot and edit in DV, and save the MPEG2 encoding to the very end, when you are compressing the video even further in order to create a DVD. If done properly and if the video image is relatively noise-free, you can show clean video at just 4 or 5Mb/sec without any artifacts.