MP4 versus AVCHD and bitrates - AVS Forum
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post #1 of 17 Old 04-06-2013, 07:58 AM - Thread Starter
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There is a lot of confusion about MP4 and AVCHD video formats. Some say since they are both AVC (H.264) and on most camcorders and cameras MP4 has a higher bitrate, then MP4 must be better (fewer artifacts).

This is false. Yes, both use AVC compression, but this comes in different profiles. And the profiles differ as to the degree of sophisticated compression.

AVCHD (at least the 108060p version) uses a "High" profile and uses CABAC. What is CABAC? Here is a quote from Wikipedia: "It is a lossless compression technique. It is notable for providing much better compression than most other entropy encoding algorithms used in video encoding, and is one of the primary advantages of the H.264/AVC encoding scheme."

On my camera, the higher bitrate MP4 (for the same resolution and frame rate) is 'Baseline' profile and does not use CABAC. Thus, because there is less compression, a higher bitrate is needed to achieve the same quality. Why not use CABAC? Wikipedia goes on to say: "CABAC is only supported in Main and higher profiles and requires a large amount of processing to decode compared to similar algorithms."

This is one reason why MP4 is "easier to edit" and why on some cameras with low powered processors AVCHD is not offered. And why many viewing devices (including computers) have trouble even playing AVCHD.

And, CABAC is not the only difference between 'High" and 'Baseline' - there is the number of B-slices, and number and variability of macro blocks.

So do not be fooled by bitrates; that is only one criterion for judging the quality of the codec used. For the exact same compression scheme higher bitrates are better. But MP4 and AVCHD are not just different wrappers of the same scheme; AVCHD is a far more sophisticated and efficient compression scheme than the usual MP4 version. It is possible on some cameras MP4 uses a more sophisticated scheme than AVCHD, but I have not encountered this.

I have, as have many, compared even 145Mbps well-known compression schemes (e.g., Pro Res) to 28Mbps AVCHD and found no difference (both sampling at 8-bit 4:2:0) in quality from the same camera.

So, what about .mov?....
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post #2 of 17 Old 04-06-2013, 08:04 AM
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Outstanding topic for your post #2000! You never disappoint!

It is time I understand MP4 a little better. I have ignored because all my stuff was set up around AVCHD. Adobe even got an extra $60 so I could have "full AVCHD support" in their latest NLE version.

Bill
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post #3 of 17 Old 04-06-2013, 08:23 AM
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"So, what about .mov?...."

.mov "is a common multimedia format often used for saving movies and other video files. It uses a proprietary compression algorithm developed by Apple Computer and is compatible with both Macintosh and Windows platforms."

And since AVCHD was developed by Sony and Panasonic, can we see indications of corporate bickering?

While I'm at it, I think I will try to figure out the difference between .m2ts and .mts. One source says .m2ts is "Blu-Ray" and .mts is "AVCHD".

Look how many video formats there are: http://www.fileinfo.com/filetypes/video
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post #4 of 17 Old 04-06-2013, 07:41 PM
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AVCHD is a format, which includes directory structure, naming convention, container and codecs. MP4 is just a container. You cannot compare the two.

AFAIK, there is nothing that precludes using more advanced encoding schemes with MP4 container.

P.S. I did see horrible macroblocking in 1080p60 mode from the HDC-SD600 that I used to own. I hope that in the last three years encoders have improved.
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post #5 of 17 Old 04-06-2013, 08:00 PM - Thread Starter
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Quote:
Originally Posted by Ungermann View Post

AVCHD is a format, which includes directory structure, naming convention, container and codecs. MP4 is just a container. You cannot compare the two.

AFAIK, there is nothing that precludes using more advanced encoding schemes with MP4 container.

P.S. I did see horrible macroblocking in 1080p60 mode from the HDC-SD600 that I used to own. I hope that in the last three years encoders have improved.

You can compare them (them=the MP4 video versus the AVCHD video) once you know the parameters of the compression schemes used for each container. That is the whole point - the container is almost irrelevant. MP4, as you say, could have any level of encoding scheme.

1. But, in fact, on most cameras and camcorders MP4-container video uses a less advanced compression scheme than 108060p or 108060i AVCHD video but a higher bitrate per pixel*frame. But only the latter is published as a spec, which is why people are misled.

2. Many postings in this forum keep inferring that high bitrates (for MP4 offerings on cameras and camcorders) mean less macroblocking compared with AVCHD 108060p or i. Without knowledge of the exact compression scheme it is not possible to infer how good the video will be for a given bitrate. I know you know this, but you have leaped on high bitrates as if they were always an improvement. And we can know the compression scheme once we have a video clip.
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post #6 of 17 Old 04-06-2013, 10:26 PM
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"You can compare them (them=the MP4 video versus the AVCHD video) once you know the parameters of the compression schemes used for each container." -- Exactly. You can compare only when you know the exact parameters of the compression, which makes any generalization pointless. Do you remember the GH1 blunder with crappy encoder which, reportedly, was missing B-frames? It recorded in AVCHD. But hacked to 50 Mbit/s and higher it produced decent image. I guess I am saying that unless you exactly know the details about encoding, it is safer to bet on bitrate. There is no replacement for displacement, and even crappy encoder can produce something watchable at high bitrate.

"But, in fact, on most cameras and camcorders MP4-container video uses a less advanced compression scheme than 108060p or 108060i AVCHD video but a higher bitrate per pixel*frame. But only the latter is published as a spec, which is why people are misled." -- Even if this were true, there is nothing inherently worse in MP4 compared to MPEG-2 TS (which is a container for AVCHD), so at most you should compare specific implementations.

It would be interesting to compare Canon's MP4 and AVCHD, too bad that the new camcorders cannot record 1080p60 onto both cards simultaneously, only 30p/24p.
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post #7 of 17 Old 04-07-2013, 02:04 PM
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By the way, this is what MediaInfo says about videos produced by my son's Flip-like DXG-567V digicam:

Format : AVC
Format/Info : Advanced Video Codec
Format profile : Main@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 4 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Bit rate mode : Variable
Bit rate : 4 046 Kbps
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 29.970 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Title : Ambarella AVC / Ambarella AVC

The video itself is not horrible for a $40 cam, but I would not call it HD, it looks to me as widescreen SD. I've seen better HD quality at about the same bitrate (~4 Mbit/s).
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post #8 of 17 Old 08-21-2013, 08:10 AM
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I know I am somewhat late to the thread, but I just wanted to point something out to the OP that seemed to me to be inaccurate (or at least suggesting something that is inaccurate).

You have highlighted that CABAC is a lossless compression technique. This is absolutely true, but that is not its benefit as all other entropy coding techniques (including CAVLC, used in the Baseline profile) are lossless too... they would be somewhat useless otherwise.

Once you reach the entropy coding step in video compression, you have already lost data, which is what makes it a lossy format, during what is known as the quantization step. High Profile H264 is still lossy (though there are extensions to the profile which provide a lossless option, but that is different).

The advantage of CABAC over CAVLC is that it is a more efficient coding scheme (at the cost of greater computational complexity). CABAC can more closely approach the theoretical limits of compression which Claude Shannon defined in his Source Coding Theorem (http://en.wikipedia.org/wiki/Shannon%27s_source_coding_theorem). This means you can get more efficient compression, which of course leads to the requirement of a lower bitrate for the same perceived image quality.

I apologize if you knew this already, it just came across to me by the highlighting of Lossless in the description of CABAC that you were suggesting that that was its primary benefit over CAVLC from the Baseline Profile.
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post #9 of 17 Old 08-21-2013, 10:20 AM - Thread Starter
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Thanks for the further clarification - more info is better.
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post #10 of 17 Old 08-21-2013, 10:17 PM
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Quote:
Originally Posted by Ungermann View Post


It would be interesting to compare Canon's MP4 and AVCHD, too bad that the new camcorders cannot record 1080p60 onto both cards simultaneously, only 30p/24p.

I have an HF-G30, so I checked the encoding used for the various bit rates for the MP4 and AVCHD footage.

All bit rates for AVCHD are High profile at level 4.0, except the 28 mbps mode which is level 4.2. All use CABAC.

The bit rates for the MP4 footage are as follows:

4 mbps Main profile Level 3.1
17 mbps High profile Level 4.0
24 mbps High profile Level 4.1
35 mbps High profile Level 4.2

They use CABAC as well (Note: the 17-35 mbps modes use high profile, not main)

In other words, MP4 uses the same encoding as AVCHD, but at the top end with a higher bit rate. Presumably that means the best shooting mode is MP4 at 35 mbps. You won't be able to tell the difference looking at the raw footage (mostly), but when you edit you should have more leeway with the MP4 35 mbps relative to the AVCHD 28 mbps footage.
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post #11 of 17 Old 08-22-2013, 12:04 AM
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Personaly i found no increase in mpeg4 footage over avchd,only a lot less rcording space on cards,even 28mbps was no gain over 24mbps in quality,i am intrigued as to what the editing gains are,more leeway for colour correction ?.
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post #12 of 17 Old 08-22-2013, 01:30 AM
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H264 is Mpeg4 layer 10, ref wiki: http://en.wikipedia.org/wiki/H264

Problem is, no consumer camera has the internal processing power to compress H264 all that well, and huge compromises are made. A lesser compromise is to allow higher bit rates, eg the Canon's 48Mbs, but the H264 compression is still weak, and can fall apart quickly when grading in post (this happened to me yesterday). The only real way to get a good image is to film as close as possible to the final look you want.

This is why shooting in RAW will become the norm for pros and enthusiasts.
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post #13 of 17 Old 08-22-2013, 02:54 AM
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I agree that shooting with uncompressed or relatively uncompressed format is better, which is why the 35 mbps is a better option in this case, not because it improves the raw footage quality but because it gives you more room for editing. But the problem is that the cameras that can shoot like that make poor camcorders, and so far no manufacturer has addressed that issue satisfactorily.

I think it is something that will happen in 2 or 3 years from now, but for now you have to compromise one way or the other. It is starting to happen though, we are beginning to see camcorder like features being incorporated into still cameras, such as the upcoming D70. There are still lots of things that need to happen though, the question of ergonomics, sensor cooling, data bandwidth etc etc. The D70 is still a video solution stuck in a still camera body, so we have a way to go.

For solutions like BM's products, there are additional questions that I would be concerned about, such as dust management and stabilization (due to the fact that as cameras, they are quite primitive).
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post #14 of 17 Old 08-22-2013, 06:53 AM
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Quote:
Originally Posted by flintyplus View Post

Personaly i found no increase in mpeg4 footage over avchd,only a lot less rcording space on cards,even 28mbps was no gain over 24mbps in quality,i am intrigued as to what the editing gains are,more leeway for colour correction ?.
I found subtle differences in the 35Mbps MP4 vs the 28Mbps AVCHD on the G30 when shooting a tree with the sky background. In the AVCHD, the sky was compressed to be more uniform in color whereas in the MP4 the color gradations were better preserved. It was a subtle effect. Note that the 28Mbps AVCHD on the X920 was also able to preserve the color gradations in the sky, so this is a property of Canon's H.264 encoder rather than a limitation intrinsic to h.254 itself.
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post #15 of 17 Old 08-22-2013, 12:55 PM
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Quote:
Originally Posted by hatchback View Post

I found subtle differences in the 35Mbps MP4 vs the 28Mbps AVCHD on the G30 when shooting a tree with the sky background. In the AVCHD, the sky was compressed to be more uniform in color whereas in the MP4 the color gradations were better preserved. It was a subtle effect. Note that the 28Mbps AVCHD on the X920 was also able to preserve the color gradations in the sky, so this is a property of Canon's H.264 encoder rather than a limitation intrinsic to h.254 itself.

With all the tests i have done i get none of the differences you describe,in case its my eyes i have had others double check.
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post #16 of 17 Old 08-22-2013, 12:57 PM - Thread Starter
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Quote:
Originally Posted by hatchback View Post

I found subtle differences in the 35Mbps MP4 vs the 28Mbps AVCHD on the G30 when shooting a tree with the sky background. In the AVCHD, the sky was compressed to be more uniform in color whereas in the MP4 the color gradations were better preserved. It was a subtle effect. Note that the 28Mbps AVCHD on the X920 was also able to preserve the color gradations in the sky, so this is a property of Canon's H.264 encoder rather than a limitation intrinsic to h.254 itself.
in today's world, if you are going to make a claim about something better than something else in video, you can just show us. So, upload these videos and let us see for ourselves. And also tell us if you did any post-processing (if you did, do not bother uploading since that alone can make for differences).

And color gradations - sky is a classic example - are a function of chroma sampling, not bitrate (how many colors [4:2:2 versus 4:2:0])
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post #17 of 17 Old 11-29-2013, 01:36 PM
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There's something about the AVCHD and mp4 issue I don't manage to see quite clearly : assuming that AVCHD is better, when it comes to editing, FCP requires you to transcode it. Won't it loose the advantageous quality it'd had over mp4 ?

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