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I have a video that was created on a surveillance camera with the (for video) unsusual resolution of 1280x1024. It's encoded with H.264 and encapsulated in an MP4 AVC container. The quality is rather good, especially considering the difficult structures in the image (the fine steel structure of a radio telescope dish and dark branches against the sky).

I tried to cut it using iMovie, but all export methods I tried so far yield very bad quality videos. The comparison below shows the original footage (left) and the best result I achieved until now (right). This was created by using the built-in exporter and specifying a "large" video. Note the greatly decreased resolution and blurred structures.

A section of the original video Encoding result using built-in exporter of iMovie

There are many hints on the net that suggest using QuickTime export, but I was not yet able to get any better quality out of it. I tested:

  • DV output format -- blurry, and the aspect format changed even though I specified an output video size of 1280x1024
  • H.264 output -- extremely blurry, even on highest quality setting and with two-pass encoding

So my question is: How can I tell iMovie to simply cut the input video without re-encoding it, or alternatively: How do I tell iMovies built-in exporter to use a different video format than "large" (720x576)?

File size is not an issue here.

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  • What do you mean by “cutting” exactly? Extracting a sequence of the video (time cutting) or a detail from it (space cutting)? – MattiSG Jan 12 '12 at 15:23
  • Here, I mean "time cutting" only, although "space cutting" would be neat, too. -- Metaquestion, since I'm not a native English speaker: Wouldn't "space cutting" usually be called "cropping" in this context? – jstarek Jan 12 '12 at 20:40
  • Not a native English speaker either and, being in a rush, I indeed forgot about the term “cropping” ;) – MattiSG Jan 12 '12 at 21:01
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Indeed, you should use QuickTime rather than iMovie: iMovie will import (and therefore usually encode) the movie, but will also force you to export, as you have noted.

The main interest of using QuickTime is to use its editing features.

Assuming you're using QuickTime X (Snow Leopard / Lion), open your movie file, and hit ⌘T (or Edit > Trim). The timeline will morph into a yellow double-ended scrollbar so that you can trim the sequence.

Quicktime X trim bar

Adjust it to fit the sequence you want, and validate the trimming with a click on the Trim yellow button. You can then simply save the file (⌘S), without the need for an export that will necessarily reduce quality.

Update seeing that you need to remove parts of the video.

You'll need the more advanced editing features of QuickTime 7. To install it on Snow Leopard or Lion, refer to Installing QuickTime Player 7 on Mac OS X v10.6 or Later on Apple's KB.

You'll then be able to open your video with QT7, select parts of your video with I (set input point) and O (set output point), and delete the part with a stroke of ⌫. Then, simply save the file, as said earlier.

You might need a license key for QT7, though (I don't remember if the latest versions of the OS need them or activate the Pro features for free).

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  • Interesting feature, I didn't know about that -- however, it seems that Quicktime can only cut one segment out of the video. This is not quite enough for my use case; I need to cut the original material up into several pieces. – jstarek Jan 12 '12 at 22:34
  • So the question of losslessy cutting video may become a recombining one in combination with this answer... – Jason Salaz Jan 12 '12 at 23:42
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    MattiSG, when I trim the video by selecting a portion in the middle (excluding the beginning and end), the window title changes to Untitled and Command-S doesn't work. Trying to close the window brings up a prompt about unsaved changes and forces me to export, which as you said causes a re-encode. – Kartick Vaddadi Aug 13 '12 at 5:23
  • @KartickVaddadi Under which app? Which version? In which format is the original video? – MattiSG Aug 14 '12 at 8:47
  • Quicktime X (not 7) on Lion. The original format was mp4. – Kartick Vaddadi Aug 15 '12 at 13:19
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The free and open source AviDemux video editor is a better software to cut or join AVC (H.264) / HEVC (H.265) encoded MPEG-4 videos without re-encoding them again (note: re-encoding is necessary if the "cut" you make is not on a start and end KEYFRAME. With AviDemux, you can easily use the UP and DOWN arrow keys to jump to all the keyframes in a video, and thus easily select the right portion between keyframes you want to delete from the video).

AviDemux can also produce better quality encoding with smaller file size, unlike Apple apps, as they can also encode using the CPU (Apple apps often turn to the built-in hardware encoder to encode media - this is blazing fast but at the price of lower quality and bigger file size.)

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