So how much 720p video can the 32g iPhone hold?

Discussion in 'iPhone' started by BConvery, Jun 14, 2010.

  1. BConvery macrumors regular

    Feb 28, 2009
    Can anyone with experience on how big these files are give an estimate how much video the new iPhone will hold at 720p, 30fps? Its the main reason I'm upgrading and just wanted to know if 32gig's held hours or minutes worth of video. I suspect the latter....

  2. appleguy123 macrumors 604


    Apr 1, 2009
    15 minutes in the future
    We need to know about the compression used before we can give you a solid answer.
  3. Knowimagination macrumors 68000


    Apr 6, 2010
    for very basic reference... the flip mino records 720p at 30fps and their 8gig model holds 2 hours of video
  4. trajen macrumors 6502a

    Oct 2, 2008
    Here is a great article explaining your question!

    With iPhone 4’s improved camera and HD video, should I go 32GB? (updated)
    by Justin Horn on Jun 11th, 2010 @ 10:45 am
    One year ago today, I created a post to help those getting ready to buy the iPhone 3GS decide if going 32GB was worth the extra $100. Today I’m going to ask the same question of the upcoming iPhone 4 using the same template as last year.

    The iPhone 3GS at 3MP has an average files size of about 1.3MB. The move to 5MP should make the average size about 2.7MB. So assuming you have 500 pictures on your iPhone the difference between the 3GS and 4 would be about 700 MB, not that big of a deal for that amount of photos. So just like the 3G to 3GS, the improved camera isn’t a reason to grab the 32GB model.

    Video recording on the iPhone 3GS is VGA quality, 640 x 480 at 30 frames per second. This is the same as the new front facing camera on the iPhone 4. The calculations are assuming the same 24 bit depth as the previous models.

    Using the same formulas as last year to calculate the size in kilobytes (KB) of one frame of uncompressed video:

    Frame size K = ( [Pixel Width x Pixel Height x Bit Depth] / 8 ) / 1024

    Where 8 represents an 8-bit byte, and 1024 equals the number of bytes per kilobytes.

    To determine the file size of one second of uncompressed video, multiply the image size by the number of frames per second (fps).

    To determine how compression affects file size, divide the file size by the compression ratio.

    Me on the compression ratio last year:

    Based on my research I found the compression ratio of standard MPEG-4 is about 30-40:1 and the newer H.264 (or MPEG-4 AVC) which the iPhone uses is about 1.5 – 2x better. For my cacluations below I will use a H.264 compression ratio of 60:1, just about in the middle of what I found.

    This 60:1 ratio I calculated last year turns out to be a bit too high when looking at actual videos from the 3GS. Part of this might due to the fact that I’m not calculating the audio portion of the recording, but in practice a compression ratio of 40:1 is very close for the average recording.

    NOTE This ratio might be off if the compression algorithm has been stepped up on the iPhone 4 with it’s speedier CPU, but this should be a pretty close estimate.

    So let’s recalculate the 3GS size and compare that to the 4. This year let’s take a more moderate 250 mins of video usage vs the 500 I used last year. This would be about 50, 5 minute videos.

    UPDATE A lot of comments I’m getting that 250 minutes is a crazy amount for a phone. This is just an example and assumes keeping videos on your camera roll and building them up over time. I know after 6 months or so my camera roll gets filled with hundreds of pictures and lots of videos. So yes, you can download them off the phone at any time, but I like to have videos and pics on my phone to show people. To make it easier to calculate how much you think you will use, I’ve added storage needed for 1 minute. So, for example, if you think you only need 30 mins of video on your iPhone 4 you are looking at: 89 MB * 30 mins…only 2.6 GBs.

    iPhone 3GS video size for 250 mins:

    ( [640 x 480 x 24] / 8 ) / 1024 = 900 KB / frame

    900KB/frame x 30 frames/sec = 27000 KB/sec

    27000 KB/sec / 40 compression ratio = 675 KB/sec compressed

    675 KB/sec * 250 min * 60 s / min * 1 MB / 1024 KB * 1GB / 1024 MB = 9.66 GB (39 MB / min)

    This seems to be the wrong resolution, see updated version below

    iPhone 4 video size for 250 mins:

    ( [960 x 720 x 24] / 8 ) / 1024 = 2025 KB / frame

    2025 KB/frame x 30 frames/sec = 60750 KB/sec

    60750 KB/sec / 40 compression ratio = 1518.75 KB/s compressed

    1,518.75 KB/sec compressed * 250 min * 60 s / min * 1 MB / 1024 KB * 1GB / 1024 MB = 21.73 GB (89 MB / min)

    UPDATE In the comments below and elsewhere people have been questioning my use 960 x 720 for the iPhone 4 HD resolution because the standard 720p is 1280×720. I was assuming Apple would stick with the same aspect ratio of the iPhone 3GS for video, 4:3. 720 in 4:3 ratio is 960. The new digital camera still shoots in this 4:3 aspect ratio as seen in the sample pictures on Apple’s website. So really I think this could go either way, but below I present the amount of storage that would be used if the iPhone 4 were using true 720p HD quality.

    UPDATE 2 Watching the demo in the keynote, it looks like the video is in 16:9 aspect ratio. Guess all my naysayers were correct, but I’m happy to be wrong on this one…I’ll take letterboxed playback on the 1.5 aspect iPhone vs the weird 960 x 720 resolution I was thinking.

    iPhone 4 video size for 250 mins if true 720p (1280 x 720):

    ( [1280 x 720 x 24] / 8 ) / 1024 = 2700 KB / frame

    2700 KB/frame x 30 frames/sec = 81000 KB/sec

    81000 KB/sec / 40 compression ratio = 2025 KB/s compressed

    2025 KB/sec compressed * 250 min * 60 s / min * 1 MB / 1024 KB * 1GB / 1024 MB = 28.97 GB (118 MB / min)

    If a higher 60:1 compression ratio is used by the more powerfull iPhone 4: 79 MB / min

    So as expected more than doubling the resolution more than doubles the size of the video. So with the HD video recording even 64 GB could be a limiting factor. Hey Apple, were is our 64 GB version of the iPhone 4?

    So like last year, the jump in the still camera mega pixels won’t affect your space enough for you to warrant an upgrade to 32GB if you are currently happy with your 16GB iPhone, but if you are planning on shooting a decent amount of video…that’s a different story. When you factor in all storage you’re already using for apps, music, and pictures you aren’t left with much. Even with a 32GB model most people won’t be able to hold anything near my calculated 250 mins which would take up about 60% (more like 90% with true 720p) of the total storage. So with this in mind I can’t recommend saving the $100.
  5. BConvery thread starter macrumors regular

    Feb 28, 2009
  6. thelatinist macrumors 603


    Aug 15, 2009
    Connecticut, USA
    Judging by the bitrate they use for their current 640X480 video (about 3500 kbps), I'm guessing they'll use about 10,500 kbps. That translates into about 4.5 GB/h.
  7. gloss macrumors 601


    May 9, 2006
    Yeah, by way of comparison, the Flip UltraHD records 720p at about a 9Mbps bit-rate on average, gives you about two hours on 8GB of internal memory, which would extrapolate to about 420 minutes in 28GB of space.

    Wait, someone already said that. Agh.
  8. iMJustAGuy macrumors 68020


    Sep 10, 2007
    Beach, FL
  9. dizzy13 macrumors 6502

    Jul 9, 2008
    Glad you found my post useful. Hopefully my 79/MB - 118/MB per min estimate is pretty close.
  10. Prosser macrumors newbie

    Jun 23, 2010
    OK, from a quick test with the iPhone 4, it is actually recording video in 1280x720p (24bit Color) at 29.97fps encoding with H.264 within a Quicktime mov container at a bitrate of 10638kbps of video + 64kbps of mono audio = 10702kbps total. In human readable format, that’s 1.306 MegaBytes per second of recording or 78.383 MegaBytes per minute. In short this all translates to using 1 GigaByte of space for recording every 13.06 minutes of 720p high def video on the iPhone 4.

    It does not look like you can email or MMS the actual true HD video out of the phone. To pull the actual HD Video you need to connect your phone to your computer and pull it off manually. If you email your video from your phone, the iPhone 4 will compress the video down to 568x320 at 30fps in H.264 - Quicktime .mov file at a total bitrate of 783kbps (Much smaller at 5.73MegaBytes per minute video)
  11. dizzy13 macrumors 6502

    Jul 9, 2008
    Yeah, looks like the low end of my estimate was right. They really stepped up the compression in the iPhone 4 over the 3GS.

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