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AVCHD video compression

Discussion in 'Filmmaking' started by AndyWear, Jan 24, 2014.

  1. AndyWear

    AndyWear TalkEmount Rookie

    24
    Jan 1, 2014
    Hi guys,
    I did some googling but I'm still not sure I understand.

    From what I read, AVCHD is a bad video compression because of the low bit rate. But why does bit rate matter? From what I see in my videos, they look pretty good.
    As for Canon 5d 3, you get these .mov files that I think are uncompressed with higher bit rate? Are higher bit rates meant for Color grading? Why does higher bit rate matter for color grading?
    And since AVCHD is no good, is there a way to convert into another file with a higher bit rate, or is this already too late and the loss of quality can't be returned? Thanks

    -Andy

    EDIT: I have Sony A7 btw.
     
  2. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    Austria
    AVCHD is a pretty efficient compression, which in itself is not necessarily bad. A 24Mbit/ s AVCHD video will in most cases be of higher quality than a video in another format with the same bitrate. The problem is that even AVCHD 2.0 does not support bit rates larger than 28Mbit, which is pretty low. The reason for it is probably that a 24Mbit AVCHD file already needs huge amounts of processing power (the other big downside of the format). And with a compression as high as AVCHD, you loose the ability to color grade the files almost completely.

    You can convert it to other formats of course (some apps, like FCP X, even do this automatically to reduce the processing power needed afterwards), but the quality won't improve.

    In conclusion, it's good for people who want to document their life without editing the files bc it saves storage and still has a high quality, but it's horrible for people who want to work with the files.
     
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  3. AndyWear

    AndyWear TalkEmount Rookie

    24
    Jan 1, 2014
    So I can't get cinema like quality using this current avchd compressoin? I was planning to do a lot of color grading but I'm not too sure how bitrates affect color grading. I hope there's a firmware that can change all this. Whats the reason we're stuck with AVCHD and not other formats?
     
  4. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    Austria
    You won't get 'cinema like' quality out of any camera at this price point, except maybe the Blackmagic Pocket Cinema Camera or the Panasonic GH3/4. Not much color grading you can do with NEX videos.

    I doubt a firmware can change this, as it would probably need some hardware changes too. But even if it was possible, Sony won't do it. Why? AVCHD is the codec they developed themselves to differentiate between the Handycam / SLR / NEX-cameras and the much more expensive XDCAMs, which shoot Apple ProRes 422 or lossless. Even some of their €5000 handycams shoot only AVCHD, although I think they are starting to change this with new models now.

    If you want awesome quality video out of a less than a thousand bucks body, buy the BMPCC: http://www.blackmagicdesign.com/products/blackmagicpocketcinemacamera
     
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  5. Imasphere

    Imasphere TalkEmount Regular

    62
    Jan 22, 2014
    I work in broadcast television as a video editor and here are just a few comments. Please keep in mind that I am not a codec specialist so I might be mistaking on a few specifications but I'll still try to explain what I know. First of all XDCAM is not limited to ProRes or 422 lossless but it is a 4:2:2 or 4:2:0 codec which means that the sampling is done 4 times for luminance and 2 times for colours. In comparison HDV is a 4:1:1 codec. All XDCAM is based on mpeg2 but the bit rates can vary from 30 to 50 bps depending on the type of XDCAM. In most cases (though not always) XDCAM is intraframe which means that each image is compressed individually. As for AVCHD it is an mpeg4 format with variable bit rate which is interframe. This basically means that the camera analyses a frame every let's say 10 frames and only takes into account what has been changed in the next 9 frames. In other words, if you are on a fixed street shot and a car goes by, most of the background will stay the same and only a portion of the image will change so only the portion of the changing image will be written down into data and the rest will be based on the first frame. In other words AVCHD takes up less space on a disk or SDcard for a given quality but compression artefacts will be more frequent. Now for the color grading element. Since avchd is interframe and all adjacent frames alway refers to a given I frame which makes it very hard for a video editing software to manage this type of compression scheme. Some video editors allow direct editing of interframe formats but many require that you convert the footage from interframe to intraframe, that way each image will be compressed individually and the software will not have to look at the reference image each time it plays. Once you have converted the footage, it is easily possible to colour grade it. You must keep in ind that the original footage has an 8 bit colour depth and that most pro formats use a 10 bit depth but that doesn't mean that colour grading is impossible, just not as precise. It's kind of like comparing colour grading in raw and jpeg, both can be done but you will have more artefacts in jpeg. So now that the more technical terms are out of the way. Here is my hands on experience. First of all there are no more standards in broadcast television. It is now not uncommon to see some footage taken from YouTube and used on a broadcast show. Is the footage quality good? No but broadcasters don't seem to care which is kind or ironnic when they are always saying how great hd is. But for what I work on, a scientific documentary show and a lot of the footage is shot with a Canon 5D mark II. The Canon also uses an mpeg4 based interframe codec but at higher bit rates (I think it is around 45 bps) but still has only 8bits of colour depth. The images are then converted to an XDCAM 50 intraframe codec. The images we get from that camera are remarkable. The cameramen really know how to use the 5D and they have the choice of quite a bit of really good lenses for each type of shot they are trying to get. They also shoot with a Sony F55 camera which is a much more expensive video only camera but I find the 5D images are often better because of the lenses used.
    So basically I think you can shoot some very good footage with the NEX cameras but, just like in photography lens quality really matters. Will your footage be of cinematic quality, I don't think so but will it be of broadcast or television quality, yes because broadcasters don't adhere to specific standards anymore so if your video is nice looking it can be broadcast. Will you be able to colour grade your footage? Yes but not as effectively as with footage you would have shot with a RED or a Black Magic.
    If you want some good advice on how to set your camera for optimal color grading possibilities here is a link to a great tutorial I found on Vimeo which shows the possibilities of the NEX6 and the settings you should use. This was shot at a wedding and I haven't tried the settings yet but the guy's footage looks great.
     
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  6. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    Austria
    Imasphere, thanks for your additional comments, but you forgot a few things. First, the codec is not everything. One camera with a 28 Mbit/s AVCHD codec might give you a wonderful video quality, while another one with the same specs and lens might give you nothing usable. There are many things in play here - sensor architecture, downsampling codec if applicable, rolling shutter effects and so on. Second, you cannot really compare a 5D to a NEX. The 5D has much bigger pixels and because of its size a much better heat handling which, in turn, allows for higher quality, better downsampling and higher bit rates.

    As for lenses - of course everybody would love to shoot with Arri Zeiss Master Primes (and I doubt there's ANY Canon lens out there that rivals those lenses), but nobody here is able to afford them (€70.000+ for a prime, €200.000 for a zoom is not uncommon), but all in all, shooting with lenses optimized for photography will be a disadvantage. When handled right and respecting it's limitations, you'll get just as good pictures as when shooting stills though.

    Color grading - Imasphere, did you ever work with files from NEX cameras? You can't really color grade them at all. Sure you can give a slight hue here and remove a slight color hue there, but you can't really 'grade' individual colors to your liking. At least not with DaVinci Resolve, the color grading solution of my choice, and I don't know any better software for that, so I doubt anyone could do much more.

    It's not hard to get 'broadcast' quality nowadays, which is also due to the limited bandwith broadcasters have for publishing the content. But to get 'cinema like' quality, well, look elsewhere.

    A short note on the 5D: Dr. House was entirely shot on Canon 5D MKIIs, and it looks gorgeous in HD. So you CAN shoot great footage with such cameras, although for artistic purposes, they're FAR too limited. Like I said, the BMPCC or better the Blackmagic Production Camera are cheap solutions for getting that 'cinema' quality.
     
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  7. Imasphere

    Imasphere TalkEmount Regular

    62
    Jan 22, 2014
    No I haven't tried doing any color grading on the NEX but I'll try in the near future. You are right that he will not be able to grade individual colors but an overall acceptable look should be attainable. I agree with you that the Blackmagic is probably the most cost effective solution of getting great video. I still think that for most uses his camera should be able to give great footage. You won't have the dynamic range or possibilites of the Black Magic but for most uses it should do fine. The one thing we don't know and maybe the OP could answer this is what do you intend to use this video footage for? If it's for a wedding or corporate video it should do fine, if it's for a prime time TV series it won't do. I haven't ran into the camera heating issue because is just bought my NEX6, and right now in Canada its freezing cold, but this probably going to be hard to work around.
     
  8. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    Austria
    100% agree with you this time. As for the overheating issue, it was quite a big problem when shooting a concert video a few weeks back, so be aware of that - it usually happened after about 6 minutes video on my NEX-7. Usually only shoot well planned out short films or ads, so never was a problem before.

    And yes, it can give great footage - used NEX cameras for several paid video shootings (one of them was a commercial ran in cinemas) and never heard a complaint about the quality.
     
  9. Imasphere

    Imasphere TalkEmount Regular

    62
    Jan 22, 2014
    6 minutes! I did not think the overheating issue was so fast. I had heard of this issue but thought it occurred after 20 or 25 minutes. I am planning to take a trip in South-west USA in July and I know it's going to be insanely hot down there at that time of the year. I was counting on doing a few time lapse sequences along the way. Do you know if the heating issue is less of a problem in time lapse mode? If you ever come up with tricks to minimize this issue, they would be great to know.
     
  10. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    Austria
    I shot at about 23° C, so not that hot either. Although I heard it is different between all the new NEX models how long it takes until they overheat. Btw., took about half a minute until I could start shooting again, but turned off between four to six minutes then. Luckily, shot the event with three cameras, so no problem after all.

    As for time lapse - and I assume you do it with shooting photos - it's no problem at all. You can even burst through the 10 fps of the NEX-6 as often as you want, it will never overheat. The overheating really ONLY occurs when shooting longer video sequences.
     
  11. Imasphere

    Imasphere TalkEmount Regular

    62
    Jan 22, 2014
    Yes time lapse in photo mode then assembly of the pictures in a Quicktime movie. Sure glad the time lapse feature isn't as prone to overheating.Once it gets warmer over here I will test my camera more thoroughly. Thanks for the comments.
     
  12. AndyWear

    AndyWear TalkEmount Rookie

    24
    Jan 1, 2014
    Hey guys,
    I want to be able to get my visuals like Ray Roman's Wedding videos. Just wondering if this would be attainable. I actually have an A7, not a NEX, any difference in the video qualities?
    http://rayromanfilms.com/theater/


    I'm actually getting confused now by what "cinema" like quality is after reading all this.lol
     
  13. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    Austria
    From my experience, you'll be able to get comparable color and motion to Ray Roman's videos, but the video won't be as sharp, not even with the best lenses (this is not a problem usually, as our brain is used to not perfectly sharp video, but his videos seem incredibly sharp). But don't forget that a huge part of a good video is the stabilization (steadicam or other solution) - and he seems to use a VERY good, expensive stabilization system -, the master plan (i.e. the script) and the light.

    As for the A7, it has comparable video quality to a NEX-7.

    To the 'cinema'-like quality: This is a very subjective definition (please correct me if I'm wrong). To me, it simply means being able to shoot with a flat profile, getting a huge dynamic range in 24 progressive frames a second that hold a ton of detail, sharpness and color information to be able to fully tune the video to look and act like it was shot for a blockbuster production.
     
  14. Imasphere

    Imasphere TalkEmount Regular

    62
    Jan 22, 2014
    Sorry about the A7 confusion. You could probably get a similar look with really good fast lenses and if your really good at tweaking your camera. Did you look at the Vimeo tutorial I sent you. I think that guy does a really good job with his footage. One think to take into account is that you shouldn't just consider the camera part. In the Ray Roman films he uses a lot of cameras with jibs, tracks and steadycam shots. This is surely not a $2000 wedding video more like a 5 figure job. I don't know what your experience is but I shot videos for three of my friends' weddings and I found they were hard to do. I know I don't want to do them anymore. A lot of people put down wedding videographers considering them like amateurs but in my book a very good wedding filmmaker is hard to beat. Why are weddings so hard to do? First of all, you just have one take, then you usually have to use the available lighting and the sound is also a major issue especially when you hear background music on your shoot. Every time you cut your footage in the editing room the sound also cuts and you end of hearing the song in shuffle mode.. You are also dealing with people who usually know nothing about video production, who are expecting something that looks like a scene from Downton Abbey but aren't willing to pay more than $1500.
    I know I am being a bit cynical and my goal is not to discourage you, but rather to let you know what to expect. I think you can still make a decent wedding video on a limited budget but I don't think they will look like the Ray Roman films. You definitely want to use two cameras for the ceremony and get a lot of cut away shots of the guests to help out in editing. What I used to do is put one wide angle camera on a tripod at the back of the church and just let it run. I would then use my hand held camera for the closer shots. That way you always have a cut away shot and get continuity in your sound. The only problem with the tripod camera is that if you use a dslr or mirrorless camera your shooting time is limited by the size of your SDcard unless you have someone else operating the camera. You might also want to put wireless mics on the bride and groom.
    Anyways, I hope this helps. Be sure to show us a sample of your film once it's done.
     
  15. Imasphere

    Imasphere TalkEmount Regular

    62
    Jan 22, 2014
    Seems like we were answering the question at the same time, but we pretty much gave the same answer.;)
    One other thing Andy should consider and I forgot to mention is to have a shutter speed that has the same frequency as his lighting. A multiple of 50 in Europe and a multiple of 60 in North America.
     
  16. Imasphere

    Imasphere TalkEmount Regular

    62
    Jan 22, 2014
    I just saw a user review on the Canadian Sony website. The user says he has solved his overheating issues by using a Memory Stick Pro card instead of SDHC. Just thought it might be an interesting thing to know. The only problem is that the Memory Stick Pro cards I saw were only 16Gb and they were expensive too. I also often wonder if these posts are not written by some marketing guy at Sony. Anyone tried the Memory Sticks?

    Sent from my Nexus 4 using Tapatalk
     
  17. slothead

    slothead TalkEmount Top Veteran

    544
    Mar 1, 2015
    Maryland
    Tom
    I've got what is probably a dumb question, but let me blurt it out...

    Up until now I have been using PS CC to edit my MP4 video and it works fine as far as I can tell, but now having acquired a couple little Sonys, I find this "new" (for me anyway) AVCHD (and even more recently the a5100's XAVCS) is not apparently readable by PS and I am wondering how I can edit them. I could convert them to MP4 probably, but I could also just set the cameras to record in MP4 to begin with, but I suspect that I am losing some quality doing either.

    What do you guys do with the AVCHD and XAVCS (without major dedicated movie software resources)?
     
  18. Imasphere

    Imasphere TalkEmount Regular

    62
    Jan 22, 2014
    In my case, I use the Sony Camera software to convert to mp4 and then run it right through Final Cut Pro. If it is a big project, I convert the footage to Prores 422 which is easier on the computer CPU. All this conversion leads to added compression but it's the best work flow I've found. Ideally, I would have liked to convert directly from AVCHD to Prores but the software I have doesn't seem to allow this.
     
  19. BrorSvensson

    BrorSvensson TalkEmount Regular

    106
    Feb 6, 2015
    Avchd is not a problem, only if you are shooting a very flat look/log and grading you will notice the difference, if you are going to post the content online avchd is absoulotely enough