What's the simplest/fastest way to split an mp4 file into two files?

April 8, 2017 12:29 PM

I have a large video file (mp4) that I'd like to make into two smaller video files. This seems like it should be simple to do. I've got Adobe Premiere Pro CC, but I don't really know how to use it. I think I'm getting it to do what I want but it's going to take a couple hours to just process and render half of the file, and even then, I'm not 100% positive that the results will be the same quality as the original. Is there a way to do this that doesn't require rerendering the entire video? I've seen lots of freeware out there, but I don't really trust the results of a Google search for this sort of thing. Okay, I'm almost embarrassed at the stupidity of this question.

I've seen some questions about how to do this in bulk, but I don't really need that. Also, some questions for similar topics that are really old, but I figure things have changed a bit in the past 7 years or so.

posted by ErWenn to Computers & Internet (11 answers total)

Go with Premiere. Any other system will be just as much a learning curve. This should not be hard to do.

What's large? Hours? Hundreds of GB? Very large is going to take time on anything, even heavy pro systems. But, splitting into two should not be rendering, there's an extraneous step that you're triggering.

Load it into the timeline, find the point to split, slice at that point, remove one side and do a "save as" or export, be sure it's to the same format and codec that the original is in.

One thing, find a small video of the same format to figure out the steps.
posted by sammyo at 12:40 PM on April 8, 2017

Response by poster: What's large? Hours? Hundreds of GB?

The file's about 23GB. So not enormous, but big enough that rendering seems stupid.

Load it into the timeline, find the point to split, slice at that point, remove one side and do a "save as" or export, be sure it's to the same format and codec that the original is in.

That's what I tried to do the first time. Unless I'm missing something, "Save As" only gives the option to save a "project" file. I used the Export → Media option and chose "Match Sequence Settings" to keep the format and codec the same. That's what triggered the hours-long rendering sequence. There must be an option I'm missing somewhere.
posted by ErWenn at 12:50 PM on April 8, 2017

Freeware mp4tools will do this. Mp4splitter is specifically for this purpose.
posted by bluecore at 12:53 PM on April 8, 2017

On reflection yes go with one of the freeware splitters. Premeire may not work with mp4 natively, thus possibly auto converting to it's working format (fast) but without specialized hardware mp4 compression is very cpu intensive.

(mp4 compression takes a key frame at full resolution but the next n frames are deltas, just the bits that changed, until a new key is needed.)
posted by sammyo at 1:38 PM on April 8, 2017 [2 favorites]

With the proper codecs installed VirtualDub will open mp4 files in various formats if you need a GUI. Last I saw, which was years ago, it would only cut on GOP boundaries if you want to avoid a full reencode, though. You'll want the ffmpeg plugin to make it read/write mp4 and mkv.
posted by wierdo at 3:40 PM on April 8, 2017 [1 favorite]

Best answer: The answer is almost always ffmpeg.

$ ffmpeg -i input-video.mp4 -codec copy -ss MM:SS -to MM:SS output.mp4

There are many possible options, a google search for 'ffmpeg extract' or similar will turn up more specific or complicated examples.
posted by zengargoyle at 4:47 PM on April 8, 2017 [7 favorites]

I'm in a teaching program and I've been using MPEG Streamclip to take recordings of entire classroom sessions (about 2-3 GB files) and trim them down to smaller clips which can then be exported separately. It had basically no learning curve: mark the "in" and "out" of your clip, tell it to "trim", and then tell it to export that clip. Then undo your trims and start again on the next clip.

When you export you'll get detailed video options for what type of file and what quality rate you want, with good presets also.
posted by The Pluto Gangsta at 5:32 PM on April 8, 2017

Seconding ffmpeg. If you use the copy codecs, your files will write basically as fast as the hard drive. The data in the frames will be bit-for-bit identical to the original. Stack Overflow question
posted by RobotVoodooPower at 6:30 PM on April 8, 2017 [1 favorite]

ffmpeg is the tool you want.

But if you want to use Adobe Premiere, look at what codec you have inside the MP4 wrapper and check if it will work with Smart Rendering.
posted by Rainbo Vagrant at 3:02 PM on April 9, 2017 [1 favorite]

oh, if command lines intimidate you there's WinFF as a frontend to ffmpeg.
posted by Rainbo Vagrant at 3:06 PM on April 9, 2017 [1 favorite]

Response by poster: ffmpeg worked like a charm! Thank you!
posted by ErWenn at 3:57 PM on April 9, 2017