user3335: What application is there that can open a video, modify it, and save it?
(the software that I am using now, only allows the video to be used as a source, and then exported)
I have adobe premier, but it does not actually edit videos, you have to make a new project, and set the output type/settings, then import the video, then bring in the video, edit it, and then save it.
I also have iMovie, and again, project, import, edit, export.
Is there any application that I can open a mp4 video make edits (clipping segments) and save it in the same format/size/container/etc as it was opened in?

user3029: What do you mean by "Edit"? If splitting/cutting all you need, take a look at
AVS Video Remaker, which makes it without conversion.

user25532: AVS4YOU and Filmora can do this but they are 60USD. 
Avidemux can do this for free (and the above software may even be reboxed Avidemux) but it will only cut one video where as these others will cut your video into lots of clips, saving each separately. 
There is also losslesscut which is a GUI for  ffmpeg seems to be able to do all that the commercial stuff does for free. You press the "i" and "o" (in and out) keys to set a cut, and press the c+ button to set a second cut. 
https://github.com/mifi/lossless-cut
Unfortunately it does not seem to work with the video that I have created using Vegas. 

user2178: Open your video in Quicktime Player, click Edit -> Trim and place the start and end marks at the desired beginning and end of your clip. Hit Trim and then click Save.

user525: If you can script yourself, all you need to do is call FFmpeg repeatedly:
ffmpeg -ss [start-time] -i input.mp4 -c copy -t [clip-time] output.mp4

Here, start and clip times can be in the form HH:MM:SS.mmmm, or just in seconds. 

To give you a rough idea how that'd look like in Ruby, see this Gist of mine. It contains a script that takes an edit list, a folder of videos, and cuts them accordingly. I've used it very often for cutting videos based on an input edit list.
The edit list would look like that, with the timestamps in the proper FFmpeg format (e.g. 00:00:24.240) and the difference passed to -t in the last column.

Note that you can't expect it to work with any input/output without synchronization issues. If that's the case, you need to re-encode video and audio parts. I wouldn't use that script of mine though as it's not very … eloquent in that regard. Rather cut your video in a NLE.

3335: <p>What application is there that can open a video, modify it, and save it?<br>
(the software that I am using now, only allows the video to be used as a source, and then exported)</p>

<p>I have adobe premier, but it does not actually edit videos, you have to make a new project, and set the output type/settings, then import the video, then bring in the video, edit it, and then save it.</p>

<p>I also have iMovie, and again, project, import, edit, export.</p>

<p>Is there any application that I can open a mp4 video make edits (clipping segments) and save it in the same format/size/container/etc as it was opened in?</p>
 3029: <p>What do you mean by "Edit"? If splitting/cutting all you need, take a look at
<a href="http://avs-video-suite.org" rel="nofollow">AVS Video Remaker</a>, which makes it without conversion.</p>
 25532: <p>AVS4YOU and Filmora can do this but they are 60USD. </p>

<p>Avidemux can do this for free (and the above software may even be reboxed Avidemux) but it will only cut one video where as these others will cut your video into lots of clips, saving each separately. </p>

<p>There is also losslesscut which is a GUI for  ffmpeg seems to be able to do all that the commercial stuff does for free. You press the "i" and "o" (in and out) keys to set a cut, and press the c+ button to set a second cut. 
<a href="https://github.com/mifi/lossless-cut" rel="nofollow noreferrer">https://github.com/mifi/lossless-cut</a>
Unfortunately it does not seem to work with the video that I have created using Vegas. </p>
 2178: <p>Open your video in Quicktime Player, click <code>Edit -&gt; Trim</code> and place the start and end marks at the desired beginning and end of your clip. Hit <code>Trim</code> and then click <code>Save</code>.</p>
 525: <p>If you can script yourself, all you need to do is call FFmpeg repeatedly:</p>

<pre><code>ffmpeg -ss [start-time] -i input.mp4 -c copy -t [clip-time] output.mp4
</code></pre>

<p>Here, start and clip times can be in the form <code>HH:MM:SS.mmmm</code>, or just in seconds. </p>

<hr>

<p>To give you a rough idea how that'd look like in Ruby, see <a href="https://gist.github.com/2574696" rel="noreferrer">this Gist of mine</a>. It contains a script that takes an edit list, a folder of videos, and cuts them accordingly. I've used it very often for cutting videos based on an input edit list.</p>

<p>The edit list would look like that, with the timestamps in the proper FFmpeg format (e.g. 00:00:24.240) and the difference passed to <code>-t</code> in the last column.</p>

<p><img src="https://i.stack.imgur.com/M01G8.png" alt=""></p>

<p>Note that you can't expect it to work with any input/output without synchronization issues. If that's the case, you need to re-encode video and audio parts. I wouldn't use that script of mine though as it's not very … eloquent in that regard. Rather cut your video in a NLE.</p>
