FORUMS: list search recent posts

confused about codecs!

COW Forums : Compression Techniques

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
jaime abramson
confused about codecs!
on Feb 24, 2009 at 9:34:12 pm

I'm trying to put together specs for clients sending advertising spots (:30s, :60s, you know how it goes) to our master control center electronically. Obviously we'd prefer uncompressed video but would like to give DV compression specs for space saving and faster file transfers.

I'd like to specify preferred codecs for (not so bright) clients to use, and as I'm researching this I'm getting more and more confused. Just listing DV50 or DV25 compression isn't enough, but there seem to be so many different codecs out there that it wouldn't be right to only accept one or two codecs. And on top of that, I've read in some forums that people rever to "the DV50 codec" which is somewhat confusing to me. Are there standard specs for compressing to a DV25 file or a DV50 file that I should give rather than listing off different codecs like Panasonic, Main concept, Canopus, etc?

In short, if any of you super smart people were to tell a not-so-tech-savvy client the kinds of compressed files you'd accept, keeping in mind the file will be compressed for air once we receive it, what would you say? Any advice would be much appreciated!





Return to posts index

Craig Seeman
Re: confused about codecs!
on Feb 24, 2009 at 10:48:09 pm

So much can go wrong if they truly don't know what they're doing.

Why not use DGFastchannel for spot delivery?
If they used Telestream Episode (either Mac or Windows) they can get a preset from either DG or Telestream and the program will encode to DG specs. They can then FTP the file to DG and they will then deliver the spots to the TV/Cable stations.

There are other compression apps that can do this too but key is being able to hand the client a preset to use in their compression app.

Typically MPEG2 Program or Transport Streams would be good although depending on the ingest H.264 Program or Transport streams may be in order.

Of course you could ask for an 8 Bit Uncompressed file as long as you provide a way for the client to FTP the file and you can handle any unforeseen variations unknowing clients can come up with.



Return to posts index

Craig Seeman
Re: confused about codecs!
on Feb 24, 2009 at 10:58:02 pm

DGFastchannel




Return to posts index


Chris Blair
Re: confused about codecs!
on Feb 25, 2009 at 3:57:34 am

We encode videos and upload to FastChannel and Vyvx all the time. Like Craig said, they both prefer an MPG2 program stream. Prior to getting into it (3 years ago) we just did a few test files and when we got one that met FastChannel and Vyvx's specs, (and ours for quality), we saved it as a preset and were off and running. We've encoded and uploaded as many as 50 spots in one day without issue.

The great thing about MPG2 is it's a fairly tight spec (not a lot of choices to screw up), is well-known and fairly well understood, and is widely compatible with every NLE system out there. So your clients should be able to handle getting you files that look right and play correctly. There could be some field reversal issues here and there but they're very easy to spot.

On the specs...the settings we use have very slight compression, something like 18-20MB/sec, so it's much better than DVD quality. I know Vyvx preferred 4:2:2, although the only way we could do that was to output the file from our NLE systems (VelocityQ) as a native uncompressed file, then go into Procoder or Carbon Coder to compress to 4:2:2 MPG2. It took too much time and there were color conversion issues to deal with as well. So we just settled on the 4:2:0 MPG2 at the high data rate.

Some people output Quicktimes using low compression with H264 (which looks great), but from the tests we did, it took longer, the file sizes were larger than the MPG2, and you still have colorspace conversion issues to figure out.





Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com


Return to posts index

jaime abramson
Re: confused about codecs!
on Feb 25, 2009 at 5:04:50 pm

Thanks for the help guys!

We actually do accept spots via DG and VYVX also, but would also like to give clients the option to upload to our corporate FTP site (for free, unlike DG and friends). We'll be taking the uploaded spots and using Flip Factory to compress for air.

I'm hesitant to put on our content spec sheet that we'd accept H.264s or mpeg2s or anything compressed because of the fact that we'd be compressing further for air (we make highly compressed mpeg2s similar to DVD compression). In order to ensure quality, I'd really like to stress the uncompressed side of things, but also give an option for slight compression considering it could take some time to upload/download a 2min VOD segment. That's what led me to thinking we could allow clients to use DV compression when sending spots, since we also accept DV on tape.

Am I off base in thinking this way? Should I move away from the DV compression idea and create our content spec sheet based on what Flip Factory can accomodate, even though compressing an H264 file to an mpeg2 might not be wise? Or should I go the other way and say only uncompressed material (considering most of our clients wont understand that anyway)?




Return to posts index

Craig Seeman
Re: confused about codecs!
on Feb 25, 2009 at 5:45:51 pm

Assuming time is money why create problems for yourself?
If you can handle DG than create a preset (or use one offered from DG) and hand that to the client.

You started off with
[jaime abramson] "In short, if any of you super smart people were to tell a not-so-tech-savvy client the kinds of compressed files you'd accept,"

If the client isn't tech savvy get them a preset otherwise you're walking into hours of trouble shooting and the risk of spots not making air.

If you don't give them a preset you'll enjoy the fun of getting Quicktime Reference Movie from Final Cut Pro (or other NLE) because the client thought, "hey it's smaller, it's the same quality and I checked and it played on my system."

Of course you can just tell them self contained at whatever their sequence setting is and if you can support all the codecs and custom codecs on all the NLEs on the market, that'll work too. You may well get someone saying, "The sequence is Quicktime (or AVI) so that's what I sent you."

Edit: LOL! Look at the thread above this "Quicktime not supported." That's probably one of the stories you'll see.





Return to posts index


Tod Hopkins
Re: confused about codecs!
on Feb 26, 2009 at 12:23:06 am

[jaime abramson] "if any of you super smart people were to tell a not-so-tech-savvy client the kinds of compressed files you'd accep"

Don't. Handle all conversion at your end. That's what I do. It's the only way. You've already told me the client can't handle it.

tod

Tod Hopkins
Hillmann & Carr Inc.
Washington, DC


Return to posts index

Chris Blair
Re: confused about codecs!
on Feb 26, 2009 at 2:54:30 am

On the idea of asking clients to give you uncompressed files: It ain't gonna happen. An 8 bit uncompressed :30 spot, with bars/tone, slate and a few seconds of black before and after is going to be around 900MB. Even on a T1 line that's going to take 75 minutes to upload minimum. Multiply that by several versions of a spot; uploading to several different stations at the same time; uploading different client spots etc....and it just becomes unwieldy. Nobody I know has that kind of time and bandwidth to dedicate to that.

An MPG2 4:2:2 file at between 15-20MB sec will end up being less than a tenth that size, which is more manageable. Remember, that's way higher quality than a DVD, (double the chrominance, 4 times less compression on average). If you recompress for air, it should look fine. It's certainly no worse than dubbing from a NLE via component to analog BetaSP.

Even a 4:2:0 MPG2 at the same compression is very similar to BetaSP according to some non-scientific engineering tests I've seen guys post online. This discussion came up in the 2002 or so when DG and Fast Channel starting getting popular and taking away all the TV commercial dubbing and satellite uploading business from large post houses. Their argument was "quality was suffering." When some engineers tested it, to their surprise, the encoded files actually were better quality than BetaSP, by far the most popular format at the time for tape delivery, and DG's satellite delivered file was equal to what the big post houses were sending via satellite to TV stations as well. End of arugment.



Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com


Return to posts index

jaime abramson
Re: confused about codecs!
on Feb 26, 2009 at 3:36:20 pm

I'm sold, hit bitrate mpeg2 it is :)

I had no idea the quality loss in recompressing for air would be that minimal. Our MCC currently masteres EVERYTHING to BetaSP (why? because we're so at the leading edge of technology!) so comparable or better quality would be a great thing for us.

I figure I'll say uncompressed material preferred, although Chris has got a point about download/upload time. So uncompressed media delivered on disc or external drive is preferred. And for sending via FTP I'll make some mpeg2 presets. I also like the thought that there aren't too many mpeg2 specs to screw up :)

Thank you all for the help!



Return to posts index


Chris Blair
Re: confused about codecs!
on Feb 26, 2009 at 8:56:58 pm

On the quality issue. I'm not trying to say that MPG2 compressed spots are pristine. They're not. But in the big scheme of things, they're not horrible either and likely are on par with any analogue master you're currently getting, and close to most digital dubs as well.

If you come out of a NLE system via SDI to a DVCPro50 or DigiBeta deck, the signal remains digital but it does get transcoded and recompressed when recorded to the specs of that particular format.

So if you went back and forth between a Digibeta master and your NLE system via SDI (even if you're capturing uncompressed in the NLE), the signal will evenutally (25-30 passes?) start to degrade noticeably. Compression gurus also say there's a transcoding "hit" that takes place, where the codec going into the NLE has to re-code the data...so when you go back out to the deck, it has to re-code back into it's algorythym of choice (Note: some people argue this doesn't introduce loss; while others insist it does).

I'm probably not getting all the technical terms and processes correct, but as long as a compressed format is being used somewhere in the "chain" there will be some loss. Heck, engineeers argue there's even some slight loss when tanscoding between one uncompressed format to another due to the re-coding of the file. I'm not too sure about that one, but that argument can be found if you look hard enough online.

But bottom line is that it's being used everyday for spot delivery and transmission for networks and local affiliates alike.


Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2017 CreativeCOW.net All Rights Reserved
[TOP]