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If I have an existing MP4/H264 video file and I need to trim the start and end,

Then save it as an MP4 again,

Are there any recommendations on export settings?

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You can use ffmpeg, a free command-line tool, to do this

Without recompression

ffmpeg -ss 02:45 -t 03:05 -i orig.mp4 -c copy -map 0 -avoid_negative_ts make_zero cut.mp4

This will copy a 3m 5s portion of the original MP4, starting at 2m 45s. Since the codec of the video stream in a MP4 usually uses temporal compression, the cutpoints may not be exact and some frames before and after may be included in the trimmed file. Since there's no recompression, quality is identical to the original.

With recompression

ffmpeg -ss 02:45 -t 03:05 -i orig.mp4 -c:v libx264 -crf 20 -c:a aac -b:a 128k -map 0 cut.mp4

This will precisely cut the specified portion but will recompress the content. The crf value controls the video quality - smaller value produces better quality but a larger file. The b:a sets the bitrate of the audio output.

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  • this sounds awesome - just googled the steps involved in setting up ffmpeg on my mac and it looks a tad 'challenging' – any non-command line apps available? – alexh Apr 21 '16 at 3:01
  • You can download a binary from my first link - no installation needed. Specifically - evermeet.cx/ffmpeg – Gyan Apr 21 '16 at 4:43
  • Downloads are .7z files. Not sure what to do with these... – alexh Apr 22 '16 at 0:35
  • Wondering if there are any paid GUI apps? – alexh Apr 22 '16 at 0:36
  • 7z files are compressed archives like ZIP. Get 7zX from 7zx.updatestar.com and extract the files. – Gyan Apr 22 '16 at 5:10
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You can also use MPEG Streamclip for simple editing tasks like that. Just open your file, set in and out point and export again.

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    Does MPEG Streamclip allow for trimming/saving/uncompressing MP4s? Thanks – alexh Apr 22 '16 at 1:29
  • Well, if it is as simple as selecting a "middle" part of a video - thus cutting off a part of the beginning and the end, it does. Just give it a spin, the software is free and can be downloaded without charge. – Hans Meiser Apr 22 '16 at 1:31
  • Yes - just trimming bits off - so is it just 'save as mp4' with maximum quality settings for no compression? – alexh Apr 22 '16 at 1:33
  • I don't quite understand the export part of your question. There is no such thing as an uncompressed mp4 file. You can save the video uncompressed but typically not in an MP4 container. So if you mean "compressed but with a good quality", suggesting you some settings would require to know the size of your video frame (SD, HD, 4k?)... Generally, converting to a higher bitrate than the video was originally recorded in will obviously not make the video any better then it is. – Hans Meiser Apr 22 '16 at 1:38
  • As the source file is already an MP4, I'm looking to retain as much quality as possible. Wasn't sure what best export/save settings are when resaving an MP4 as MP4 again from MPEG Streamclip. – alexh Apr 22 '16 at 1:58
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Yes, use MPEG streamclip! You can set your in and out by using the I and O keys and export to many different codecs. The website is http://www.squared5.com.

I've been using it professionally for years.

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