how do i replace part of mp4 file

[cns00]

i have an mp4 video file which has length of 3:48:10.594. a part of the video file is corrupted and blurry. i have another video file which and that part is ok in the second file

i need to cut out a part of the second file and i want to put the good part instead of the corrupted part in the first video file and the length of the first video file has to remain 3:48:10.594 after the replacement happens

both video files have different encoding

what is the simplest way to make the new video which has the good part and it allows me to precisely select frames? i tried to do by using avidemux. the new video file had different length than the original file and it gave me warning that the part that i want to add has different encoding

[ProWo]

Post a Mediainfo of both files, specifying the corrupt one (with exact last time in hh:mm: ss for the good part) here.

[abolibibelot]

If those video files have different parameters preventing them to be merged, and if you want the cut-and-paste to be perfectly accurate, then obviously, at least the replacement segment needs to be reencoded so as to match the parameters of the first video. As for how to precisely select cutting points with a 1 frame accuracy, it could be done with a non-linear editor, or with Avisynth + AVSPMod (first adjust the required parameters on the second video to match the first video, then use StackHorizontal or StackVertical to display both videos on the same frame, Trim some frames at the beginning to have both versions synchronized if needed, then scrub to the beginning of the problematic part, note the frame number – adding the number of trimmed frames if applicable, then the same for the end of the problematic part). The difficulty, if you want to avoid re-encoding the first video, is that you can only cut on key frames ; you could be lucky as key frames are often placed at scene changes, otherwise the transition may be noticeable ; you can also decide to re-encode both videos, which makes the editing easier, then it can be done entirely in Avisynth. If using the Avisynth method, then ffmpeg could be used (with the AVS script as input) to encode the replacement part, then merge it with the beginning and end of the first video, or to encode the whole fixed video in one go.

[butterw]

Cut into 2 parts with avidemux, starting on a keyframe for the second file. This is easy enough to do but you'll end up with 2 files.
If it is not satisfactory you need to re-encode.

[ProWo]

Only as an idea (not tested):
You could remux the two mp4 (from butterw's suggestion) as TS and merge the ts files.

[abolibibelot]

You could remux the two mp4 (from butterw's suggestion) as TS and merge the ts files.

How could it change anything with regards to key frames ? I mean, if the TS is a mere remux, the encoding scheme should be unchanged, hence the interval between two key frames should be the same, shouldn't it ? (Not tested either — how scientific we are over here !)

[ProWo]

How could it change anything with regards to key frames ? I mean, if the TS is a mere remux, the encoding scheme should be unchanged, hence the interval between two key frames should be the same, shouldn't it ? (Not tested either — how scientific we are over here !)

Those who can read have a clear advantage...

[smrpix]

TMPGenc Smart Renderer can be used to split up and reassemble the clips with minimal re-encoding. It is frame accurate. From what I understand videoredo will do the same but I am less familiar with it. Most free tools will have you hunting down keyframes for days.