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Old 7th June 2017, 16:57   #23  |  Link
GMJCZP
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Quote:
For the GOP size the FFmpeg default is 12
Thanks manolito.

Quote:
Using a GOP size of 15 or 18 I found that the slightly better compression for larger GOP sizes does not make up for the loss in quality, especially for GOP 18. It would be nice if FFmpeg had an Auto-GOP feature like HCenc...
Set de GOP size change the frame structure, IMHO is more safe put g=12, 15 or 18, given the fps of the video input, and I agree with you that FFMPEG should also have the AUTOGOP feature. That's why I use sc_threshold and b_sensitivity for "manually" set the GOP and thus try to emulate the AUTOGOP function of HCEncoder.

For curiosity, here is a extract of the HCEncoder help:

Quote:
*AUTOGOP
parameter goplength (8 – 18) type integer
Status not required
Default 15 (12 for 23.976 fps)
Example *AUTOGOP 12
This command sets the maximum GOP length to be used by the autogop algorithm.
Running in AUTOGOP mode means the encoder tries to distribute the I, P and B frames in an
optimal manner based on the activity of the frames.
Encoding using AUTOGOP will be DVD-compliant if the next values are used:
• For NTSC source to be pulldowned, use values 12 – 14.
• For PAL source a maximum value of 15 should be used.
• For 29.97 NTSC source the maximum of 18 can be used.
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I hate the FFmpeg documentation...
Lol, I recommend the MPlayer help for these things.

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I reuploaded a modified version of my test bench script
Thanks, I'll have a look at it.
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Last edited by GMJCZP; 18th June 2017 at 16:59.
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