Skipping I-FRMs?

[tomthumb]

Version 2.6.15 64-bit
Windows 10

I have some H264 encoded mp4 files, opened with Avidemux. When seeking keyframes, it seems to "skip" some I-frames.

For example:
The first frame has a timestamp of 00:00:00.041 and is noted as an I-FRM.
https://drive.google.com/open?id=0B5DI5ie1Gb9qVkVVb19qVmZtREk

I press the double arrow button to go to the next keyframe, which takes me to another I-FRM with a timestamp of 00:00:05.380
https://drive.google.com/open?id=0B5DI5ie1Gb9qd0tqTnp0R1VFWmM

BUT,
If I press the single arrow backwards until 00:00:03.378, there is another I-FRM.
https://drive.google.com/open?id=0B5DI5ie1Gb9qb3NmbUpWWFM4OEU

There are many of these skipped I-FRMs throughout my videos.

I could be misunderstanding the difference between keyframes and intra-frames, but my quick research on Google indicates they are synonymous.

This happens whether I use the gui button, the keyboard keys, or the Go menu->Next Intra Frame

If I cut a section ending on one of these skipped I-FRMs and save, Avidemux gives me a warning about corruption of the resulting file. However, that file seems to play just fine in VLC.

I have not been able to find anyone else with this issue through using Google or the forum search.

Here is a sample video: https://drive.google.com/open?id=0B5DI5ie1Gb9qN0x6SmpQWHpEMVU

Here is an admlog.txt: https://drive.google.com/open?id=0B5DI5ie1Gb9qNVg2N2FsNWFmbUU

Has anyone else noticed this behaviour? Or am I doing something dumb?

[eumagga0x2a]

Thank you for the sample, confirming the behaviour on Linux both with hwaccel enabled and with the software decoder.

[Jan Gruuthuse]

I can confirm the behaviour as described by you.
I-FRM @ 00:00:03.378
Selecting keyframe is done with up/down arrow, so many do not come in that situation.
If you do want to cut on other frames not presented as keyframe by avidemux (up/down arrow key), you need to re-encode and not use the Video Output [Copy] mode.

Time permitting developer(s) could have a look at this. (see reply just above)

[mean]

I frames are not necessarily IDR
i.e. navigation point

[tomthumb]

Ah. I'm now reading up on IDR frames. That probably explains it.

Thanks for your help

[eumagga0x2a]

Thank you for the explanation on my part too. Wonder if the displayed frame type could reflect this difference.