Author Topic: Ouput Keyframes  (Read 186 times)

hansolocambo

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Ouput Keyframes
« on: September 22, 2018, 07:04:57 AM »
Hi  ;)

In order to trim and output a lossless (copy) video, it's better to cut on keyframes to avoid pixels corruption.

In most mp4 videos downloaded here and there, if I press Up / Down in Avidemux to jump from keyframe to keyframe, they're often set every 10 seconds or so. But in some other videos I downloaded, keyframe was set every 1 or 2 seconds. Which is VERY ! convenient when it comes to cutting/trimming precisely (without re-encoding).

Is it possible in Avidemux to change the original video keyframing without changing codec/compression, etc. ?
This way one could set a new keyframing (which would suppose a re-encoding I guess) before lossless-ly trimming videos.

I'm aware that playing with I-Frames options in the ouput configuration is what I want, but after reading a few articles about I-frames, GOP, and so on, I'm still a bit lost.

Could someone please explain simply  :-\  how to use Gop Size and I-frame Threshold options and what those really mean ?

Thanks !
« Last Edit: September 22, 2018, 07:31:11 AM by hansolocambo »

eumagga0x2a

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Re: Ouput Keyframes
« Reply #1 on: September 22, 2018, 09:36:43 AM »
Quote
Is it possible in Avidemux to change the original video keyframing without changing codec/compression, etc. ?

Not without re-encoding the video, obviously, as the type of compressed frame is determined at the moment of encoding.

Smaller GOP sizes allow better seek granularity and strongly reduce compression rate.

hansolocambo

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Re: Ouput Keyframes
« Reply #2 on: September 25, 2018, 08:49:07 PM »
Thanks eumagga0x2a.

I indeed managed to get the result I wanted putting much lower values for the GOP sizes.
Not sure what the i-frame is about then. I did some tests changing that value and couldn't really see any difference.

Cheers. Thanks for the answer.