Examine the GOP structure of a MPEG2 file

[themoog]

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

[jagabo]

GSpot.

[themoog]

brilliant thats what i was looking for thanks a lot

[Perry Tanko]

GSpot is very helpful, it has all kinds of uses.

But what would examining a GOP structure possibly find?

[themoog]

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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[El Heggunte]

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.

[themoog]

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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[pandy]

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.

[themoog]

thanks Pandy, 500/40=12.5 so that sounds about right.... now i know where that recommendation comes from

[pandy]

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!