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How accurate is the amount of space indicator?

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    Christina2018

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    Hi all,

    Just a quick question- does anyone know how accurate the amount of (hours) space there is left on the hard drive is? I've got over 200 recordings and it's saying I have 10 hours left for HD- is that reliably accurate or could I come unstuck as it actually could have less?

    I've never got this near before as my old box didn't have HD and when recording SD it was never a problem as it seems to use about 1/3 of the disk space compared with HD.

    Hope that all makes sense.
    Thanks in advance.
    Christina

    | Wed 15 May 2019 14:31:30 #1 |
  2. Trev

    Trev

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    Record 10 x 1 hour shows and see if they all record/how much space is left then delete them? Then let us all know.

    | Wed 15 May 2019 15:28:12 #2 |
  3. grahamlthompson

    grahamlthompson

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    Christina2018 - 5 hours ago  » 
    Hi all,
    Just a quick question- does anyone know how accurate the amount of (hours) space there is left on the hard drive is? I've got over 200 recordings and it's saying I have 10 hours left for HD- is that reliably accurate or could I come unstuck as it actually could have less?
    I've never got this near before as my old box didn't have HD and when recording SD it was never a problem as it seems to use about 1/3 of the disk space compared with HD.
    Hope that all makes sense.
    Thanks in advance.
    Christina

    It's not accurate as bitrate varies according to the channel being recorded and what the other channels on the same Mux are showing. The available free space is dynamically shared with the other channels with the channel showing the most onerous content getting the higher bitrate (stat muxing).

    The BBC HD channels have a average bitrate of roughly 7 Mbps. I hour (3600 seconds) will produce 7 x 3600 Megabits = 25200. 1 byte is approx 8 bits so the hour is about 25200/8 Megabytes (MB) 3150MB or roughly 0.3 GB. So work out roughly how many Gegabytes you have left divide by 0.3 to get hours. The Commercial channels have a higher bitrate so will use more storage.

    H264 encoders have improved greatly so are able to use lower bitrates than previously.

    The FVP units can auto delete the oldest content to make room for new recordings.

    You don't say what size hard disk you have in your unit so without this key info hard to say.

    | Wed 15 May 2019 19:59:45 #3 |
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    Christina2018

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    Sorry, it's a 5000t 500gb.

    I think I'll just try to watch some of HD recorded programmes (rather than the SD ones) for a while and then hopefully it'll free up more space. There is just so much good TV at the moment and now I've gotten used to HD I tend to opt for that rather than SD if it's available.

    Trev- I think as I record so much at different times it'd be hard to find an opportunity where by doing it if I did run out of space I wouldn't miss something I actually wanted to record.

    | Thu 16 May 2019 9:40:35 #4 |
  5. grahamlthompson

    grahamlthompson

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    Christina2018 - 53 minutes ago  » 
    Sorry, it's a 5000t 500gb.
    I think I'll just try to watch some of HD recorded programmes (rather than the SD ones) for a while and then hopefully it'll free up more space. There is just so much good TV at the moment and now I've gotten used to HD I tend to opt for that rather than SD if it's available.
    Trev- I think as I record so much at different times it'd be hard to find an opportunity where by doing it if I did run out of space I wouldn't miss something I actually wanted to record.

    This is a fairly typical BBC-HD 1 hr recording. A ITV one will be a little larger. It's from satellite though Freeview-HD won't be much different. Freeview-HD is a mix of interlaced and progressive and the main audio is AAC (advanced audio codec rather than Dolby Digital (aka ac3)).

    General
    ID : 1 (0x1)
    Complete name : D:\Test Dr Who\Doctor Who_20121225_1713.ts
    Format : BDAV
    Format/Info : Blu-ray Video
    File size : 3.29 GiB
    Duration : 1 h 1 min
    Overall bit rate mode : Variable
    Overall bit rate : 7 625 kb/s
    FileExtension_Invalid : m2ts mts ssif

    Video
    ID : 5400 (0x1518)
    Menu ID : 6941 (0x1B1D)
    Format : AVC
    Format/Info : Advanced Video Codec
    Format profile : High@L4
    Format settings, CABAC : Yes
    Format settings, RefFrames : 4 frames
    Codec ID : 27
    Duration : 1 h 1 min
    Bit rate : 6 862 kb/s
    Width : 1 920 pixels
    Height : 1 080 pixels
    Display aspect ratio : 16:9
    Frame rate : 25.000 FPS
    Color space : YUV
    Chroma subsampling : 4:2:0
    Bit depth : 8 bits
    Scan type : MBAFF
    Scan type, store method : Interleaved fields
    Scan order : Top Field First
    Bits/(Pixel*Frame) : 0.132
    Stream size : 2.96 GiB (90%)
    Color range : Limited
    Color primaries : BT.709
    Transfer characteristics : BT.709
    Matrix coefficients : BT.709

    Audio #1
    ID : 5401 (0x1519)
    Menu ID : 6941 (0x1B1D)
    Format : AC-3
    Format/Info : Audio Coding 3
    Format settings, Endianness : Big
    Codec ID : 6
    Duration : 1 h 1 min
    Bit rate mode : Constant
    Bit rate : 192 kb/s
    Channel(s) : 2 channels
    Channel positions : Front: L R
    Sampling rate : 48.0 kHz
    Frame rate : 31.250 FPS (1536 SPF)
    Bit depth : 16 bits
    Compression mode : Lossy
    Delay relative to video : -844 ms
    Stream size : 84.9 MiB (3%)
    Language : English
    Service kind : Complete Main

    Audio #2
    ID : 5402 (0x151A)
    Menu ID : 6941 (0x1B1D)
    Format : MPEG Audio
    Format version : Version 1
    Format profile : Layer 2
    Codec ID : 3
    Duration : 1 h 1 min
    Bit rate mode : Constant
    Bit rate : 256 kb/s
    Channel(s) : 2 channels
    Sampling rate : 48.0 kHz
    Compression mode : Lossy
    Delay relative to video : -828 ms
    Stream size : 113 MiB (3%)
    Language : nar

    Text
    ID : 5404 (0x151C)
    Menu ID : 6941 (0x1B1D)
    Format : DVB Subtitle
    Codec ID : 6
    Duration : 1 h 1 min
    Delay relative to video : 2 s 100 ms
    Language : English

    As you can see it's just under 3GB. Incidentally the bitrate is about the same as the best SD channels from a few years ago on satellite.

    When your box is of of warranty it's a 25 min job to drop in a 2TB drive.

    As you can record up to 4-HD channels at once even 2TB (2000GB) is easy to fill.

    | Thu 16 May 2019 10:35:21 #5 |
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    Christina2018

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    Thank you Graham- you clearly know your stuff!
    How odd that an ITVHD programme would be slightly larger in size, I assumed they'd all the same depending on how long they were rather than what channel they were on.

    I'm managing to watch around the same as I'm recording at the moment so I'm on 9 hours of HD left now.

    I deleted The Last Leg (HD) this morning and even though it was 1 hour 5 minutes the amount of hours left to record didn't change so I'm guessing that answers my own question - that it's not 100% accurate.

    | Tue 21 May 2019 13:46:25 #6 |
  7. grahamlthompson

    grahamlthompson

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    Christina2018 - 2 hours ago  » 
    Thank you Graham- you clearly know your stuff!
    How odd that an ITVHD programme would be slightly larger in size, I assumed they'd all the same depending on how long they were rather than what channel they were on.
    I'm managing to watch around the same as I'm recording at the moment so I'm on 9 hours of HD left now.
    I deleted The Last Leg (HD) this morning and even though it was 1 hour 5 minutes the amount of hours left to record didn't change so I'm guessing that answers my own question - that it's not 100% accurate.

    Presumably the BBC have more ADVANCED AVC encoders, these are capable of providing similar quality to the commercial operators at lower bitrates.

    A programme with a lot of movement (like football) will also be larger as it steals bitrate from more sedentary content from other channels on the same transponder/Mux. Rapidly changing content needs a higher bitrate to avoid obvious motion artefacts.

    As the bitrates are lower the files for the same recording time will be a bit smaller.

    This might explain how it works

    https://sidbala.com/h-264-is-magic/

    | Tue 21 May 2019 16:32:30 #7 |
  8. grahamlthompson

    grahamlthompson

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    To summarise

    Due to the number of variables involved sticking to Freeview as an example. There is no possible to way know in advance how much space will be used to record your future recording schedule.

    1 The Mux that is being used to record the content. THE PSB Mux by nature of the generally lower bitrate the encoders used will tend to make the recordings smaller.

    2 Com muxes will tend to create larger recordings due to the lower efficiency of the encoders used.

    3 In both cases the final recording size will depend on the dynamic nature of the content compared to the other channels carried on the same mux. (Stat muxing),

    If you have a HD video camera, you can minimise the size of the final recording file by using two pass recording. This analyses the whole content in two passes so is able to predict in advance where a high or low bitrate is required.

    Of course with live TV and multiple channels this is impossible.

    All you can say is the technology will produce the smallest files possible giving the highest possible quality within the total bit-pool available on the MUX.

    HD uses DVB-T2 modulation. A Mux using DVB-T2 has a higher total bitrate capability than one using DVB-T modulation.

    The more advanced compression codec used for 4K H265 greatly increases the capacity of a Mux.

    IP delivered 4K will use H265 compression.

    If freeview could switch to H265 there would be a lot more space, but would require new receivers for most of us.

    | Tue 21 May 2019 21:20:52 #8 |

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