MeGui GOP error

[yukukuhi]

I'm trying to convert an AVI file to H264 Mp4 using MeGui 2624. All the settings work perfectly except for the GOP setting, especially the min GOP size. I keep it at 25 but after encoding it shows only 1 & coz of that I have trouble in seeking/skipping the video file. Please help.

[LigH.de]

I don't believe that a minimum GOP size of 1 (means, there is only one IDR frame as one GOP) gives you seeking trouble: The shorter the GOPs, the easier the seeking. Furthermore, even if such short GOPs are allowed, I doubt that many GOPs would be so short. Their length may vary between minimum and maximum value, and compression efficiency will try to reach the maximum, if there is no scene change demanding a new GOP start in the middle.

And the maximum is rather a possible reason for seeking issues: Decoding may only start at IDR frames without probable decoding errors, and the further they are away, either the coarser the accepted seek positions are (if the player will only seek to GOP starts), or the longer a player needs to decode from a previous GOP start to the desired seek position before the playback continues.

A complete encoder command line with all options (or alternatively, the reported metadata from the video stream in a MediaInfo analysis) would be useful to see if you possibly selected a counterproductive options set.

[sneaker]

https://forum.videohelp.com/threads/379201-mp4-skipping-problem-in-mpc?p=2450029#post2450029

If you can't turn off open-gop it is because you have selected Blu-ray as target playback device. Don't do that. (MeGUI shouldn't force open-gop for BluRay, IMHO. It's not required.)

[yukukuhi]

I tried that but it's not working.

[yukukuhi]

@light.de
Counterproductive like what?

[hello_hello]

https://forum.videohelp.com/threads/379201-mp4-skipping-problem-in-mpc?p=2450029#post2450029

If you can't turn off open-gop it is because you have selected Blu-ray as target playback device. Don't do that. (MeGUI shouldn't force open-gop for BluRay, IMHO. It's not required.)

MeGUI doesn't enforce open gop if you check "Bluray Compatibility" (bluray_compat=1) in the advanced x264 configuration, but it appears to if you select "Bluray" from the list of target playback devices.

I'll confess I thought selecting Bluray as the target playback device enabled open-gop, but MeGUI would still let you disableit if you so desired, but it wouldn't let me disable it when I tried it recently. Maybe I wasn't remembering correctly and it's always forced open-gop that way. It's probably not a bad idea though, and not too hard to work around if you need to by creating your own encoder configuration without it.

Still, I'm not sure that's the issue in respect to the keyint settings, because for a 25fps video I'm pretty sure selecting Bluray as the target playback device will get MeGUI to use keyint = 25 and keyint_min = 1 and increasing them will have no effect. If you only set bluray_compat=1 in the encoder configuration though, MeGUI will let you change the open gop and keyint settings. That's probably what's happening as the MediaInfo from the other thread shows keyint = 250.

When bluray_compat=1 it seems keyin_min=1 is enforced. I think it's x264 enforcing it though, not MeGUI.

[LigH.de]

"Counterproductive" like: trying to limit an option which doesn't hurt (min. GOP size) but leaving an option which would have an effect; I may have been wrong to mention Blu-ray compatibility at first, as an MP4 is not directly related, but max. GOP size should have an effect for sure, and maybe also open GOPs if people say so from their experience (although an IDR* frame is the only possible (re-) start of decoding, no matter whether previous B frames refer to it or not).

*IDR = Intra-frame with Decoder Reset: You can be certain that no previous frame will matter when the decoder reaches such a frame. Decoding can start here without any reference to previous video. Therefore you can certainly seek to such frames. Vice versa, it means that if you want to seek to any other frame, the decoder needs to rewind further to the previous IDR frame and decode from there to your target frame before playback can continue. If you have a slow decoder, this may take some time. To avoid waiting, either seek to the few IDR frames only, or encode with shorter GOPs to have more IDR frames to seek to, and less frames to skip to the target frame.

[yukukuhi]

@hello_hello
Thanks for your help, it solved the problem.