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  1. Hi all, anyone got any thoughts on a tool that will show the GOP structure of a MPEG2 file and or display stats on bits per frame, VBR/CBR, null packets etc....

    Thanks in advance

    Neil
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  2. brilliant thats what i was looking for thanks a lot
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  3. Perry Tanko Perry Tanko's Avatar
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    GSpot is very helpful, it has all kinds of uses.

    But what would examining a GOP structure possibly find?
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  4. In my case I'm doing some quality testing for a client, and I've been creating some test files to match as closely as I can the house video standards.

    MPEG2 20mbps long GOP for SD playout is what I was told.

    Anyway the GOP length I would expect is 12 (for pal) but the files I've been seeing are 18, this might be reducing playout quality just a tiny bit... I just needed a tool to prove it for my report.



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  5. DECEASED
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    Originally Posted by themoog View Post
    MPEG2 20mbps long GOP for SD playout is what I was told.

    Anyway the GOP length I would expect is 12 (for pal) but the files I've been seeing are 18, this might be reducing playout quality just a tiny bit... I just needed a tool to prove it for my report.
    "GOP length = 12(for PAL)" <= from where did you get this rule or recommendation

    FYI, a lot depends on framerate, picture dimensions, and the quality of the encoder as well.
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  6. Yes I know, hence mentioning the pal FRAMERATE and I don't remember a written down rule anywhere, but most broadcasters I've worked for seem to favour 2/12.

    A quick off the cuff google search

    http://documentation.apple.com/en/compressor/usermanual/index.html#chapter=18%26sectio...5%26tasks=true

    "For most media, spacing I-frames about 1/2 second apart gives good results. This equates to a GOP size of 15 frames for NTSC and 12 frames for PAL. The DVD-Video specification prohibits GOP lengths from being much longer than this. Generally, only material with scene changes occurring less than 1/2 second apart frequently throughout the video will benefit from shorter GOP sizes."


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  7. Originally Posted by El Heggunte View Post
    Originally Posted by themoog View Post
    MPEG2 20mbps long GOP for SD playout is what I was told.

    Anyway the GOP length I would expect is 12 (for pal) but the files I've been seeing are 18, this might be reducing playout quality just a tiny bit... I just needed a tool to prove it for my report.
    "GOP length = 12(for PAL)" <= from where did you get this rule or recommendation

    FYI, a lot depends on framerate, picture dimensions, and the quality of the encoder as well.

    http://www.etsi.org/deliver/etsi_etr/100_199/154/03_60/etr_154e03p.pdf

    5.1.7 Video sequence header
    Encoding: It is recommended that a video sequence header, immediately followed by an I-frame, be
    encoded at least once every 500 milliseconds . If quantiser matrices other than the default are used, the
    appropriate intra_quantiser_matrix and/or non_intra_quantiser_matrix are recommended to be
    included in every sequence header .
    NOTE 1: Increasing the frequency of video sequence headers and I-frames will reduce channel
    hopping time but will reduce the efficiency of the video compression.
    NOTE 2: Having a regular interval between I-frames may improve trick mode performance, but
    may reduce the efficiency of the video compression.
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  8. thanks Pandy, 500/40=12.5 so that sounds about right.... now i know where that recommendation comes from
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  9. Originally Posted by themoog View Post
    thanks Pandy, 500/40=12.5 so that sounds about right.... now i know where that recommendation comes from
    as a non English native i don't know how to reply after reading http://www.businessinsider.com/why-you-should-never-say-youre-welcome-2013-11

    so perhaps: Не вопрос!
    Be Well!
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