Cut an H264 video on non-key frames

I would like to extract a scene of a video (audio codec: AAC, video codec: H264). The problem is that the scene doesn't begin on a I key-frame. The software, I have tried (Avidemux, Handbrake or VLC) allow to cut a video only on key-frames. Does anyone have a tips to solve this issue?

Thanks'

2 Answers

No way IMHO, for h.264 you have to cut at keyframes (Intra frames = I frames).

In video compression, a keyframe, also known as an Intra Frame, is a frame in which a complete image is stored in the data stream. In video compression, only changes that occur from one frame to the next are stored in the data stream, in order to greatly reduce the amount of information that must be stored. This technique capitalizes on the fact that most video sources (such as a typical movie) have only small changes in the image from one frame to the next. Whenever a drastic change to the image occurs, such as when switching from one camera shot to another, or at a scene change, a keyframe must be created.

Avidemux smartcopy mode re-encodes only the GOPs (groups of pictures) that don't start with a key frame and does a plain copy of the GOPs that do. Unfortunately, that feature is not available for AVC, only ASP.

Other software are said to do it for AVC, e.g. VidCutter but this one is working so fuzzily that I don't use it.

I tried to simulate smartcopy by merging re-encoded and copied GOP video files but the display went wrong at the merge points. It may well be that it's just a matter of re-encoding with exactly the same configuration parameters as the copy.