25 Hours HD Recording Time

Discussion in 'TiVo Series3 HDTV DVRs' started by TiVoToo, Sep 13, 2006.

  1. TiVoToo

    TiVoToo Member

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    Sep 12, 2006
    Orlando, FL

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    In MegaZone's FAQ:

    "How many hours of HD content can the S3 store?
    The S3 can store up to 35 hours of HD content. Since all digital content is recorded as-received, capacity will depend on the compression of the source material."

    I will note that the sticker on the side of the TiVo HD box that I just received states "25 Hours of HD".

    I would assume this to be the minimum. If every HD channel recorded used the entire bandwith of the transport stream (~8.2GB/hr), one should be able to store about 30 hours of HD programming on a 250GB disk. Subtract some disk space for the HD and SD Live buffers plus system overhead, and 25 hours sounds about right.
     
  2. smak

    smak TV MA SLV

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    If all you record is OTA HD, then you will get towards the low end of the scale.
    If all you record is MPEG4 HD than you will get towards the high end of the scale.

    A mixture of the two, probably puts it at 30-35 hours.

    -smak-
     
  3. msu2k

    msu2k New Member

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  4. btwyx

    btwyx Substantive Member

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    Mountain...
    Ordered.

    I emailed them yesterday asking what their plans were, and I'd take one if they did. They said they wanted to but didn't know when its available. Today's soon enough, I'll want to run the 250 for a couple of days before I swap the drive.
     
  5. Dan203

    Dan203 Super Moderator Staff Member TCF Club

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    There is no such thing as MPEG4 HD, at least not in this context. Both the ATSC and CableCARD standards call for MPEG-2 video. The only way you're going to get MPEG4 HD on this box is via some sort of download.

    Dan
     
  6. smak

    smak TV MA SLV

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    Right, i was thinking of the new D* box and the less space that an Mpeg4 HD download takes.

    -smak-
     
  7. TiVoToo

    TiVoToo Member

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    Sep 12, 2006
    Orlando, FL
    Once the S3 was powered up and completed Guided Setup, the System Info shows 32 hours of HD recording time available. Since this is the case, it is puzzling why TiVo would advertise 25 hours HD recording time on the outside of the box.
     
  8. Amnesia

    Amnesia The Question

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    My impression was that HD programming takes up different amounts of space depending on its format. (1080i taking up more space than 720p...)
     
  9. snathanb

    snathanb New Member

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    Sep 13, 2006
    That is very true. When it comes to OTA, I think it also depends oh as how many subchannels the station is running, which robs bitrate from the main channel.

    Recordings from our OTA CBS station in Dallas are by far the largest, as it is 1080i and does not have any subchannels. They run about 9 GB an hour on my OTA HD pc card. And our on FOX, which has one subchannel and broadscasts at 720p are only about 4 GB per hour.
     
  10. TiVoToo

    TiVoToo Member

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    Sep 12, 2006
    Orlando, FL
    Depends. If you get you HD over cable, your cable provider probably only transmits the 'pure' MPEG2 for the channel which varies in size depending on format. However, if you get HD OTA, the ATSC standard requires that digital transport stream (TS) maintain a constant bit rate of 19.28Mb/s. If the total 'payload' of the stream is less than 19.28, null packets are added. A transport stream may have several channels in different formats. It's up to the local broadcaster how he wants to divide the TS bandwidth among the channels. So, if your OTA recorder records the TS bit-for-bit with all subchannels and null packets, the file size for a hour program is about 8.2GB (using 'binary' GB, not 'disk manufacturer GB). My understanding is that the TiVo HD is 'smart' enough to only record a selected channel within a TS. That is, it doesn't do a bit-for-bit copy of the TS, and then extract the channel on playback. This can reduce the size of the file considerably if there are a lot of channels in the TS. I also hope it is 'smart enough' to drop the null packets when recording. If it does, then the size of a recorded DT program should be the same whether it is from cable or antenna.

    As I stated earlier, I would guess that TiVo estimates worst-case HD recording time by assuming that every DT recording uses the full ATSC bandwidth. In reality, the HD recording time should be much greater. I know that the HD DVR I built using PC parts would record about 25 hours of OTA HD programming on a 120MB disk by not recording subchannels or null packets.
     
  11. btwyx

    btwyx Substantive Member

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    I think you said what I want to say.

    The storage space depends exactly on the bit rate sent to you. That's determined by a lot of things, and format is only one of those, and there's not necessarily any relationship between format and space. So saying 720p takes less space than 1080i is not true generally.
     

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