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Quality of video transferred back and forth and WMC

Discussion in 'TiVo Home Media Features & TiVoToGo' started by MojoB, Aug 2, 2012.

  1. Aug 2, 2012 #1 of 12
    MojoB

    MojoB New Member

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    What is the quality difference between video recorded on a Tivo and video transferred to PC and back to Tivo again? Does anyone know what the resolution and bitrate are and how this compares to Windows Media Center. When I recorded straight from a Tivo (best quality) to a DVDirect (best quality) and compared it to Windows Media Center I got the following info when playing each one on a PS3:

    (I forget which one was the Tivo and which one was the WMC, I think #1 may have been Tivo and #2 WMC,
    I'll try to figure that out soon)
    1) Dolby Digital 2 Ch 48 khz 256 kbps mpeg2 7.9 mbps (not an avg, was around this range while playing)
    2) Dolby Digital 2 Ch 48 khz 384 kbps (no format given) 9.3 mbps (not at avg, was around this range while playing)
     
  2. Aug 2, 2012 #2 of 12
    wmcbrine

    wmcbrine Ziphead

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    There is no quality lost, unless you explicitly convert the .TiVo video to another format.

    Resolution and bitrate depend on your recording quality settings (for recordings from analog sources). I think "Best" is 544x480, although the DVD-based TiVos will do 704 or 720x480.
     
  3. Aug 4, 2012 #3 of 12
    MojoB

    MojoB New Member

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    I thought Tivo did a conversion when transferring to PC or is that some other type of conversion not related to quality?
     
  4. Aug 4, 2012 #4 of 12
    ggieseke

    ggieseke Active Member

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    It re-muxes and encrypts it, but no transcoding is involved that would affect quality.
     
  5. Aug 4, 2012 #5 of 12
    steve614

    steve614 what ru lookin at?

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    To elaborate, the Tivo stores recordings as seperate video and audio files.
    When you transfer the recording to a computer, the Tivo has to mux the video and audio into a single file so that it is "computer friendly".

    The encryption is necessary so that TiVo can say that they are protecting the content.
    If the end user decrypts the file and illegally distributes the content, TiVo can say "It's not our fault".
     
  6. Aug 4, 2012 #6 of 12
    lrhorer

    lrhorer Active Member

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    San...
    To elaborate still further, the format of the video on the TiVo and that of the .TiVo file are both MPEG-2, they are just muxed differently than a .mpg file and encrypted. Programs like VideoRedo or tivodecode will remux and decrypt the .TiVo file to a standard .mpg container so any old device can play it, but the bit stream that results from decoding the resultant .mpg file is precisely the same as that used by the TiVo to create its video output. Recoding the video, say to h.264 for example, can result in a loss of PQ and of course large scale changes to picture size, aspect ratio, brightness, contrast, closed captioning, etc. not to mention changes in audio volume, number of audio channels, audio bit rate, etc.
     
  7. Aug 4, 2012 #7 of 12
    wmcbrine

    wmcbrine Ziphead

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    tivodecode does not remux.
     
  8. Aug 4, 2012 #8 of 12
    lrhorer

    lrhorer Active Member

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    San...
    Oops! Of course it doesn't. I worded that badly.
     
  9. Aug 6, 2012 #9 of 12
    MojoB

    MojoB New Member

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    Jun 1, 2012
    What is the benefit of h.264 vs mpeg-2 given that mpeg-2 is the actual Tivo video format?
     
  10. steve614

    steve614 what ru lookin at?

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    Converting to h.264 reduces the file size.
     
  11. jcthorne

    jcthorne Active Member

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    h.264 video files pushed to a tivo remain in h.264 format as do webcasts and video on demand content sent to a tivo S3 and newer. Foriegn S4 units handle broadcast h.264 as well.
     
  12. lrhorer

    lrhorer Active Member

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    San...
    In general, for the same perceived PQ, h.264 files can be significantly smaller than MPEG-II. VideoRedo defaults to a roughly 30% reduction in file size when recoding from MPEG-II to h.264, allowing one to store roughly 3 h.264 videos of identical size versus 2 MPEG-II videos of precisely the same content. One can also increase the compression level in VRD. Going beyond 50% would probably produce decidedly undesirable results, however.

    Not only do the videos use less space, but when pushed or streamed to the TiVo (rather than pulled, as would be the case for TDT or pyTivo in pull mode), an h.264 video transfers roughly twice as fast as the same MPEG-II video to a Premiere, or roughly 15X real time ( 4 minutes per hour of movie) for average bit rate 1080i content. When pushed to an original S3, the video transfers more than three times as fast, or roughly 5-6X realtime ( 10 - 12 minutes per hour of movie). When pushed to a THD, the video transfers at about four times as fast, or roughly 3-4X realtime ( 15 - 20 minutes per hour of movie).

    Even 720p content, which transfers slower than any other content, can be pushed to a THD in considerably better than real time when it is coded as h.264, while the same 720p content cannot transfer in real time to a THD when coded as MPEG-II, whether pushed or pulled.

    The caveats are:

    1. Some players may not support h.264 (but most modern ones do)
    2. Pushing requires the intervention of the TiVo mind server. If it is down, which has not happened often, but has happened, pushing does not work.
    4. Pulls require a full recode, which is extremely slow. Unless the server's CPU is a real monster ( 6 cores and at least 3.2 GHz ), then don't expect pulls to occur at real time speeds.

    OTOH, vidmgr only produces pushes anyway, and IMO vidmgr is the greatest thing since sliced bread. It's all I ever use.
     

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