BlackVue DR750S-2CH

Discussion in 'DR750S-2CH' started by alexsoll, Aug 21, 2017.

  1. Ralph2

    Ralph2 Active Member

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    Evidently there is a firmware upgrade for the 750's mostly for pre production models.
     
  2. tvxr

    tvxr New Member

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    Thank you for sharing your thoughts!

    I understand what you mean and agree with you when it comes to video of a stationary scene. At the same time, if you ever had to split the video of an incident happened while driving frame by frame you might have seen that some frames are sharper than others and provide more detail than others. You get one detail from one frame, another detail from another frame and so on. This is what I mean when I am saying that 60 FPS should provide more details - it is simply twice more frames than 30 FPS with some of these extra frames providing some extra details. Therefore using higher compression for 60 FPS is senseless in my opinion, it may become a difference between been able to read other's car license plate at 30 FPS but not at 60 FPS (due to lower bitrate).

    Absolutely. If this is the decision the developers made (to sacrifice picture quality for recording time) - it was a very bad decision and is a deal breaker to me. 60 FPS at which you can read less details than at 30 FPS is unusable. Premium models of dash cams with FHD 30 FPS were good 5-7 years ago, not anymore. They have to offer either higher FPS and/or higher resolution to make new premium dash cams appealing .

    It could also be that the hardware cannot handle 60 FPS without reducing the bitrate. In that case it was an even worse decision, because if the reason for reduced bit rate is firmware - it can be fixed, but if it is hardware - there is no fix for it. Since Jeremie has not commented on this, I am afraid that this is the case.

    Exactly!
    I do not understand why recording time is even a criteria for camera which supports up to 128 GB memory cards. I am still using dash cam with 32 GB card, which provides more than enough recording time for FHD 30 FPS. I can't imagine how 128 GB may not be enough for higher resolution and/or higher frame rates, but even if it may - just focus on making a dash cam that supports bigger cards, as opposed to focusing on higher recording time at expense of the picture quality. How is this even make sense to use the latest and greatest sensor only to destroy it's output by higher compression rate later?
     
    Last edited: Sep 7, 2017
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  3. Jeremie

    Jeremie New Member

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    Hi tvxr,
    One thing I can say is that the bitrate is fixed by the firmware but not restricted by the hardware. We have tested at higher bitrates, and who knows, maybe the bitrate will evolve in the future, as was the case with the DR650S Series. Our R&D tested starting with much higher bitrates, going down progressively to match their target quality/size ratio. Past a certain point, gains in image quality were not deemed sufficient to make up for the added file size, which we have to consider since it impacts things like recording time but also Wi-Fi download speed.

    One more thing: our R&D is still working on the image optimization, so things may change in the future, but hardware-wise I can tell you we are far from reaching a cap.
    Thank you.
     
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  4. tvxr

    tvxr New Member

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    Jeremie, thank you for your comment. It still sounds like quality is sacrificed for file size at 60 FPS. If certain bit rate provides sufficient quality we still should end up having this bit rate for both 60 and 30 FPS, therefore 60 FPS files should be twice the size of 30 FPS files. If this is not the case (60 FPS size < 2 * 30 FPS size) then it'll be like saying that certain bit rate is good for 30 FPS and then all of a the sudden a much lower bit rate is good for 60 FPS, which would not make sense.

    Either way, I understand that Blackvue will unlikely change their priorities just because of this thread, but do you think if it will be possible to allow users to chose whether they want to prioritize quality over file size or vice versa (thorugh settings in firmware)? As it stands, I could not care less about wi-fi functionality or file size (128 GB should be good in any event), but I do care about quality, because quality is what determines if I will be able to read the license plate of another car or not.
     
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  5. Jeremie

    Jeremie New Member

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    You are welcome. As I said, our R&D is still working on image optimization, so things could change. However, I would like to mention that you should not expect 30FPS = X bitrate and 60FPS = 2X bitrate.
    The reason is that video compression works by comparing changes between frames. You should not think about it in terms of individual images. If you have more frames per second, there are going to be fewer differences between frames. As a result, you might not need double the bitrate to reproduce details satisfyingly.
    Here is a link to someone who explains it in details and better than me: https://video.stackexchange.com/a/12465
    And a quote from the linked text (emphasis mine):

    "With video, you have to remember that temporal information is part of the quality. If you double the frame rate, the quality of each individual frame will go down, but you will see twice as many of them and the impact of things like noise can average out amongst the frames.
    Additionally, modern compression works by comparing one frame to neighboring frames. When you increase the frame rate, the amount of change between frames is reduced, so the amount of data needed to store the change is also reduced, since less changes between frames."
     
  6. tvxr

    tvxr New Member

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    Jeremie, make sense about size not doubling at 60 FPS, because the difference in size will be due to more data describing the difference between the frames, thanks for clarifying this.
     
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  7. c4rc4m

    c4rc4m Active Member

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    It's always the case that it's quality vs file size, and there is always a point beyond which you cannot see gains, especially as other factors impact quality beyond pure bit rate, although bit rate is important. However I would make 2 points:

    1. The point of no visible gains will vary according to the amount of detail in the picture eg. a motorway picture may show no gains above X mbs whilst a tree lined route with lots of leaf detail may still show significant artefacts at X mbs because of the higher detail levels, and require a much higher data rate to achieve the same quality as X mbs on the motorway. I believe because trees are common, some argument can be made that the point of no return should be measured not against the typical urban road, but the worst road scenario ie a sub-urban / rural road that is heavily tree lined both sides

    2. You make the valid point of compromise for WiFi and file size sake. However, I believe there is an argument here for offering an extra high quality option. The whole point of firmware with multiple quality settings is it enables the user to choose which compression / quality setting best suits their needs. There's no reason why a manufacturer can't offer eg a "Full HD high quality setting" then an additional setting of "Very high" / "Insane" / "Pro" quality setting with handbook warnings that this isn't a setting for typical users, more for film-makers or enthusiasts, and it may impact recording times and download times. That isn't a licence to go stupid and just offer uncompressed video, but a licence to offer video at the very top of the gain point on tree lined roads to ensure the quality is the best possible even though it may lead to larger files sizes. As tvxr pointed out, anyone buying a 128GB or even a 64GB card isn't going to be your typical purchaser due to the cost of these cards. The beauty of firmware settings, is it enables you to offer a range of settings to suit everyone's requirements. Provided you warn people that Wifi downloads might be slow and file sizes large with "Pro" quality, and that it isn't a setting for your typical user, I don't see an issue.
     
  8. jokiin

    jokiin Well-Known Member Manufacturer

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    The challenge is that even when you tell people that some setting like hi bitrate will have an adverse effect on the ability to use WiFi they still want to complain about it, nature of the beast unfortunately
     
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  9. Jeremie

    Jeremie New Member

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    You both make good points. I always try to push internally to give customers what they want (like higher bitrates), but it's true that there is a high risk of customers complaining about the download speed if the file sizes grow too much. Also, as much as we would like to offer the best possible image quality, we have to balance recording time, microSD card lifespan, Wi-Fi download speed, reliability, heat endurance, etc.
    But again, things may evolve in the future, as they did with our previous models which received updates to increase the bitrate.
     
  10. alexsoll

    alexsoll Well-Known Member Retailer

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  11. kamkar1

    kamkar1 Well-Known Member

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    Having tried bitrates upwards of 50 mbit on a dashcam i can tell you dont really want to go there, the files that make are just huge at about 1 Gb for 3 minutes of recording.
    And 50 mbit are wayyyyy past what is sensible in relation to getting the best footage, on that dashcam based on the A7 i found 18 - 25 mbit to be about the sweetest spot.
    18 - 20 mbit are fine for just about all situations, its only when you get into those really busy situations for the poor sensor and chipset that a bit more bitrate is nice.

    So as it is now with dashcams storing on fairly small memory cards i can do without those high bitrate big files, but in the future i would not mind at least providing i can get footage off camera storage fast. ( > USB 3.0 )
    But that's still some years in the future it would seem.
     
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  12. c4rc4m

    c4rc4m Active Member

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    You'll always get someone who moans. But if you make it clear that any Pro setting is outside of normal usage range, then I don't see an issue. That's what GoPro did with their Pro setting on the Hero 2 onwards - 50mbs, with no in camera sharpening etc - essentially a Raw file. Personally, I found it unusable as I couldn't make the adjustments necessary to get a decent picture, or even a picture 1/2 as good as the much lower setting - that's the dangers of Raw files and why I wouldn't recommend that route. Shouldn't be such an issue with just high bit rate. The problem with Raw is the fact it needs colour grading because it's totally flat. However, did I or others hold it against GoPro? No because they'd made it quite clear that this was a setting purely for professional film makers, and that as such, ordinary users might find it unusable or unsuitable for their use.

    This is where encoding efficiency and especially h.265 (HEVC) comes into play. It should be possible to 1/2 the file size compared to h.264 with h.265.

    The answer to getting really large files off a memory card quickly is buy a USB card reader and take the memory card out of the camera!
     
  13. alexsoll

    alexsoll Well-Known Member Retailer

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    what processor is installed in 750s?
     
  14. BlackboxMyCar

    BlackboxMyCar Active Member Retailer

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  15. alexsoll

    alexsoll Well-Known Member Retailer

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    nothing has changed
    I thought may be something new
     
  16. jokiin

    jokiin Well-Known Member Manufacturer

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    interesting choice
     
  17. alexsoll

    alexsoll Well-Known Member Retailer

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    where can I find official confirmation of this information?
     
  18. jokiin

    jokiin Well-Known Member Manufacturer

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    Too many ¯\_(ツ)_/¯
    You would probably have to open one and check it yourself to be sure
     
  19. alexsoll

    alexsoll Well-Known Member Retailer

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    I certainly doubt it, but there is unchecked information on presence Ambarella A12
     
  20. jokiin

    jokiin Well-Known Member Manufacturer

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    I don't think A12 could support the functions they are offering on this model
     
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