FORUMS: list search recent posts

Determining what codec uses what GOP structure.

COW Forums : Compression Techniques

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
Remington Swales
Determining what codec uses what GOP structure.
on Jan 9, 2013 at 7:57:25 am

I am outputting a television show through apple compressor and was just handed a recent spec sheet for the output as we are changing the station the show airs on.

Specs:

Video Bit Rate: 12 mbps (SD) or 35 mpbs (HD)
Frame Rate: 29.97 fps (SD) or 59.94 fps (HD)
GOP: IBBPBBPBBPBB
Audio Type: MPEG1 Layer 2
Audio Sample Rate: 48000 Hz
Audio Bit Rate: 384000 b/s
Audio Channels: 2 Channel Stereo
Aspect Ratio: 4:3 (SD) or 16:9* (HD)
*On HD commercials, make sure your graphics are 4:3 as we center cut the HD signal for SD air


Typos aside, I seem to be having a difficult time determining what codec or format output will give me the best results. I am mainly wondering about how to determine the GOP sequence a codec and if it's possible to have mpeg 1 layer 2 audio on a .mov file. I'm also not understanding that audio bit rate spec.

Any help would be greatly appreciated and sorry if this is a novice question.

Much Obliged,
Remington Swales


Return to posts index

Craig Seeman
Re: Determining what codec uses what GOP structure.
on Jan 9, 2013 at 11:55:15 pm

It looks like MPEG2 Program or Transport Stream since the rest of your specs pretty much match "typical" spot delivery.

In Compressor 4 you can use
Apple/MPEG Files
and either
MPEG-2 Program stream 15Mbps or MPEG-2 Transport stream 15 Mbps
templates and copy them, make it CBR and modify the bit rate. You may need to set the field dominance since I'm not sure if Compressor would do something "dump" like make it progressive automatically. I tend to do my broadcast spot encodes in Telestream Episode since it has a lot more control.
For DGFastchannel (now DGIT) they generally ask for Program Stream for SD and Transport Stream for HD but either may work depending on the rest of your specs.



Return to posts index

Remington Swales
Re: Determining what codec uses what GOP structure.
on Jan 11, 2013 at 8:14:45 pm

Craig thanks for the response.

I was going to use the program stream prest in compressor but that gives me a .mpeg file extension. But they requested a .mpg extension. The only preset I could get that result with was MPEG-1 but it locked the aspect at 320x240.

This is being output in SD for broadcast and I think the mpeg2 compression looks much cleaner than the mp4 .mov I exported.


Return to posts index


Craig Seeman
Re: Determining what codec uses what GOP structure.
on Jan 11, 2013 at 8:21:59 pm

What you describe is why I use Telestream Episode Pro for my Spot delivery.

It's possible that the ,mpeg file will work. I'm not absolutely sure that there's different metadata since they're mpeg and mpg content are program streams to their spec.

It's possible you could just change .mpeg to .mpg and deliver and see if they accept it. It's certainly worth a shot before spending hundreds of dollars on a professional encoder... which I'd personally recommend doing since I find Compressor has many limitations.



Return to posts index

Remington Swales
Re: Determining what codec uses what GOP structure.
on Jan 11, 2013 at 8:27:49 pm

I really appreciate the advice. I may be something I need to invest in if I start outputting more tv shows but at this juncture the majority of my deliveries go to the web. I'll have to try manually changing the file extension and see if that makes everyone happy.

Thanks Again for the suggestions


Return to posts index

Remington Swales
Re: Determining what codec uses what GOP structure.
on Jan 11, 2013 at 11:05:59 pm

I looked back in compressor per your suggestion of using the program or transport stream preset and as far as the GOP sequence issue goes it does have a tab that allows me to designate the sequence I want.


Return to posts index


Craig Seeman
Re: Determining what codec uses what GOP structure.
on Jan 11, 2013 at 11:20:20 pm

And it defaults to IBBP which is basically what they're asking for.



Return to posts index

Jeff Greenberg
Re: Determining what codec uses what GOP structure.
on Jan 11, 2013 at 12:22:08 pm

[Remington Swales] "what codec or format output will give me the best results"
It really depends on your use! If you mean for it to be sourced over and over again (a digital master) uncompressed (unrealistic) is perfect. If you mean for how small you can get it and have it look good, it's an h.264 file. But that'd be disasterous for DVD playback or a Playout server that expects MPEG2.

[Remington Swales] "I am mainly wondering about how to determine the GOP sequence a codec"

Whichever software you use (by the way, which one?) may have a switch allowing you to adjust the GOP pattern.

[Remington Swales] "if it's possible to have mpeg 1 layer 2 audio on a .mov file"
It depends on the compression tool. a QuickTime file (mov) can have non-standard 'mixes' of audio and video codecs; It seems like you might be building an MPEG2 or MPEG4 file.

[Remington Swales] " I'm also not understanding that audio bit rate spec."
You have two items here - how many samples per second: 48000 - how many times the audio will be sampled.
The bit rate is how compressed the audio will be. It's set to 384 kb/s (way easier to read than 384000b/s).

I fear you're using Apple's Compressor, which is a great tool, but the wrong one here - as it won't let you get to setting the audio bit rate (or a couple of other things you're looking for.)

Best,

Jeff I. Greenberg
Editor/Author/Speaker/Consulting
My NAB seminar schedule, contact info and more


Return to posts index

Remington Swales
Re: Determining what codec uses what GOP structure.
on Jan 11, 2013 at 11:13:14 pm

Jeff thanks for the input.

I am outputting this as an SD digital file for broadcast. And I don't believe they like h.264 that much where we are sending it. So I need to just figure out how to configure a compressor preset that will conform to this spec sheet they gave me. I;d prefer to deliver a .mpg file but I work with .mov much more. Being an editor I'm not used to having to conform to GOP sequence specs.

I just want to deliver the right file, nothing worse than getting files in the wrong format.

I am outputting this from FCP through Compressor 3.5.3 (Still working in FCP Studio 2, probably going to adobe soon though)

Thanks for the help on the bit rate conversion for the audio, I set the sample rate but was thrown off because when I used the quicktime preset in Compressor it only allowed me to do audio bit rate up to 320 kbps. But upon looking at the MPEG-2 transport/program stream preset I saw the slide that lets you set your audio bit rate up to 40 Mbps.

As I'm probably gonna me migrating to Adobe this year is adobe media encoder works better than Compressor.


Return to posts index

Jeff Greenberg
Re: Determining what codec uses what GOP structure.
on Jan 11, 2013 at 11:17:17 pm

It sounds like you're making an MPEG2 transport stream (.ts) That or a muxed stream mpeg2 stream with audio (mpg)

The GOP cadence is set on the encoding part of the inspector in Compressor.

Sadly, the slider you saw? That's for the video component, not the audio.

I really don't think you can do this easily in Compressor.

Best,

Jeff I. Greenberg
Editor/Author/Speaker/Consulting
My NAB seminar schedule, contact info and more


Return to posts index

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