Saving in MPEG2 or AVCHD

[dfisher052]

This is a hypothetical question. I am currently recording camera files as MPEG2. The question is: if 1 hour of MPEG2 is approximately 4GB, how large would the same file be if I recorded it as AVCHD?

[smrpix]

That would depend entirely on the bitrate you chose to record the AVCHD files.

[PuzZLeR]

What are we talking about here?

Are we talking about 1) starting with MPEG-2 or AVCHD by recording directly to it, or 2) recording as one and encoding to the other?

AVCHD should always be smaller in file size since H.264 video is more efficient, and much more so at smaller bitrates. So, a haphazard attempt to answer your question would be:

1) Since 4GB for 1 hour of MPEG-2 is very high quality, then AVCHD at 3GB should be safe to have similar quality. The compression advantage would increase for AVCHD if you asked about 1 hour of MPEG-2 at 3GB or 1 hour of MPEG-2 at 2GB.

2) If you start with MPEG-2 and encode to AVCHD, you will never have the same quality, even at AVCHD file sizes of more than 4GB. But, for similar quality, again, the 3GB should be safe.

Keep in mind, there are alot of variables, like how much motion is in the video, etc. Also, the M2TS container typically used with AVCHD has 5%-6% overhead, increasing file size and decreasing the benefit of H.264 video under the hood - use MP4/MKV if blu-ray compatibility isn't necessary. Also, I was assuming SD, where 4GB would be too low for MPEG-2 to have decent quality at HD - in the case of HD at this duration and file size expect AVCHD to be even more advantageous.

[dfisher052]

PuzZLeR... Thanks for the reply .... My reason for asking: I am currently videoing a 1 hour program that I am capturing on a usb3 thumbdrive. Actually I come out of the camera firewire port into a computer, capture using Roxio capture program onto the thumbdrive. I'm capturing in MPEG2 but feel that I might get better quality with AVCHD. I needed to know what file size I would get with AVCHD as opposed to MPEG2.

[smrpix]

If you have the camera and the software, why not test a few different settings and see what you prefer as far as bitrate and quality. You only need to test a few minutes, then do the arithmetic to estimate your final file size.

What kind of camera are you using?

[PuzZLeR]

Again, there are many variables. What I was doing is comparing MPEG-2 with AVCHD (which is based on H.264/AVC), and comparing them ceteris paribus.

But if you're using two different cameras, you're introducing more variables. I believe even one camera that captures to multiple formats may he more optimized with one over another. As well, even Roxio may be better at one format over another if it can do both (however I don't use it so I don't know).

At any rate I too ask what camera are you using. As well, if it's a DV camera, and Roxio is outputting directly to MPEG-2 via firewire, then it's not a good option, and either will be AVCHD if that's an option as well. In this case, you start with DV and work from there.

[dfisher052]

I'm currently using a Canon GL2 (sd)., which I've been using for about 7 years, but I'm in the process of deciding on an HD broadcast quality camcorder that will take sd cards, so that will probably change how I capture. We are talking about possibly using 2 additional stationary cameras, all going through a switcher. If we do that, than we will take a feed out of the switcher into some sort of recording device, so we have all the footage on one device for editing purposes.
Since the cost of HD video has come down so much since we started 7 years ago we are updating our system from SD to HD. That also includes editing.
We are a church group that provides programming for public access TV stations in our area.

[jagabo]

Regardless of codec, frame size, frame rate, etc:

file size = bitrate * running time

With a little (~1 percent) container overhead. So for a given running time the the size of your files depends only on the bitrate you use. h.264 can achieve the same quality as MPEG 2 with about 1/4 to 1/3 the bitrate (all else being equal). But if you use the same bitrate you will get the same file size

[smrpix]

AVCHD-SD can have data rates up to 24 Mbit/s. So again, how big the file is depends on your specific settings. At the extreme end, it can be 6x larger than what you're doing now. We don't know what specific Roxio software you are using, so there is no way for us to tell what options you actually have. Do some tests.

Also, as PuzZLeR said, if you're working with DV you really should be capturing DV and then converting.

Another question, do you really need AVCHD ? Why not a simple .mp4?

Of course, this will all be moot soon when you get your new gear. Look into TriCaster if you haven't already chosen your switcher.

[PuzZLeR]

With a little (~1 percent) container overhead.

With MP4/MKV yes, but the M2TS container for blu-ray, which is also used with AVCHD, can be as high as 5% or 6%.

h.264 can achieve the same quality as MPEG 2 with about 1/4 to 1/3 the bitrate (all else being equal).

I stated the 3GB as a safe metric, which is 3/4 compression, but we could squeeze more into H.264, yes.

But I mentioned a safe metric because we're talking about 1 hour of MPEG-2 at 4GB. That's about as high a bitrate, and as good as it gets, for MPEG-2/SD at the DvD spec. I do believe the compression advantage of H.264 isn't as much at the higher bitrates - an advantage more curved than linear. The 1/3 and 1/4 compression is indeed very accurate when we're talking about lower bitrates.

Another question, do you really need AVCHD ? Why not a simple .mp4?

Other than if storing on a disc and wanting a (disingenuous at best) form of "blu-ray compatibility", then there's little reason you'd need AVCHD when a simple MP4/MKV would be much better.

Then again, AVCHD is NOT part of the blu-ray standard as some may believe. Just like DvD playback, it's no more than a feature of blu-ray players (such as MP3 playing in CD players). AVCHD was borne out of the format war long ago with blu-ray vs HD-DvD, for reasons applicable to the era then.

And many blu-ray players do have valid MP4/MKV playback (also a feature that's grown over the years). As far as I'm concerned, with the picky specs of AVCHD (such as very low GOP sizes, high container overhead, etc) then you may as well use the actual real blu-ray spec.

AVCHD is irrelevant today. If AVCHD isn't dead by now, it should be.

[dfisher052]

One of my problems is the final format I have to have. I supply 1 Access station with a standard DVD (not bluray) and the other with MPEG2 format, so that's what I need to work with. I'm currently editing the videos with MPEG Video Wizard DVD, which is why I've been capturing in MPEG2, but I'm going to start editing with Corel Video Studio X8. Actually my wife does the editing and I want something easier for her to work with. We don't need anything elaborate. The Roxio captures in either MPEG2 or AVCHD. But if there is something better that works with Corel I'm open for suggestions, but I will need a camera that can record in a format compatible with the editor.

[dfisher052]

BTW, I'm going to be away from my computer for the next 3 days so I won't be able to reply.

[smrpix]

I'm going to start editing with Corel Video Studio X8. Actually my wife does the editing and I want something easier for her to work with...but I will need a camera that can record in a format compatible with the editor.

All the more reason to capture your DV as DV, edit it, then convert it. MPEG2 and AVCHD(h.264) are both long-GOP and more difficult to edit.

Going forward, if you're upgrading your gear as you say, and you're doing a lot of this -- say one show a week or more -- you may want to consider a serious NLE like Premiere Pro or Vegas Pro, or Edius which can properly manage the spanned clips from AVCHD camcorders.

[jagabo]

All the more reason to capture your DV as DV, edit it, then convert it. MPEG2 and AVCHD(h.264) are both long-GOP and more difficult to edit.

Yes, DV devices should be captured as DV AVI. That's a simple data transfer from the camera/device to the computer. It gives you an exact copy of the video and audio on the camera. That's higher quality than typical MPEG 2 or h.264 capture and more easily edited. MPEG 2 an h.264 should be used for final delivery, not editing.

[SameSelf]

Regardless of codec, frame size, frame rate, etc:

file size = bitrate * running time

With a little (~1 percent) container overhead. So for a given running time the the size of your files depends only on the bitrate you use. h.264 can achieve the same quality as MPEG 2 with about 1/4 to 1/3 the bitrate (all else being equal). But if you use the same bitrate you will get the same file size

That is a great little formula. Here is the one I use:

X GB/hr = Y Mbps * 0.45

So, if I am recording in ProRes HQ, 220 Mbps * 0.45 = ~100 GB/hr. Then mentally divide 100 GB/hr as needed to get the file size for a 15 minute clip, 5 minute clip, etc. Or, if I choose a 20 Mbps encoding bit rate I know that is about 9 GB/hr of content.