Reducing File Size

I'm a complete neophyte at this game.  I'm making a video from an action camera image sequence ... close to 3000 images.  I need my output file to be 30MB.  It came out at 150Mb.  I tried changing the output resolution to a mere 640x360 but that only changed the size to 141Mb.  I tried changing the scale value to 40% for the sequence.  That made for a smaller output window but still 130Mb size.  Is there a way to change the resolution on all the images at once or do you have other suggestions?


  • You have an unrealistically low desired final file size.

    Assuming 30fps output, you have 100 seconds of video. For a 30 megaBYTE file, then you have a total of 240 megaBITS. That's an output bitrate of 2.4 mbps/second. 640x480 resolution is about standard definition, and a typical encoding rate for a standard def DVD would be 6-8mbps... So you can see where 2.4 isn't going to look good. 

    Why is 30 megabytes your target size? 

  • edited December 2016

    Job application,  wanted 2 minutes of video and not to exceed 30MB. 

  • Sigh. Ok, that's rough. Try 640x480 1-pass variable bit-rate. Go ahead and try a target of 2.4 mbps and a max if 3.6mbps. That'll probably be right at your target. Hopefully iit will look... Passable. 

  • edited December 2016

    I put a 1080p video through Handbrake at 640x360 (16:9) at 2400Mbps Average Bitrate and it looked perfect...apart from being small.

    I just checked and things I've downloaded from YouTube are very low bitrate. The 2016 M&S Christmas Ad is 1080p, 3 minutes long and only 50.1Mbs with a bitrate of only 2201kbps (2.2Mbps) and it's completely acceptable.

    It might be a bit  quicker to take a final version and keep on putting it through Handbrake with successively smaller bitrates, than keep rerendering it each time.

  • The only real advice I've got is export an uncompressed AVI (use ProRes if you're a Mac user) then use Handbrake to see how small you can get. On the Video tab change x264 Preset to "very slow" and try the Constant Quality @ 20. Very slow will take a long time but you will end up with a much much smaller file while still retaining quality. 

    @Palacono Changing the x264 Preset to to the slower settings kind of gets you to the same place as running it through multiple times.

  • edited December 2016

    @Aladdin4d OK, useful to know when I've got time to spend on it getting it small myself, but I didn't mean put the output back round again as a new input, I meant run it through, check the size, reduce the bitrate, rinse, repeat. :) Shame there isn't a "Set max output file size size" option, which used to be a requirement for ripping DVDs to DivX CDs back in the day... :D

  • Using a CRF/RF does not let you predict outfile file size. It is just a constant perceptual quality mode. Highly variable output depending on source input.

    I would suggest you use the two pass mode and set the bitrate(s) you need to get the file size you desire. Don't forget to include audio in the filesize computation. Then use the slowest modes of x264 to get the best quality possible at the given bitrate.

    Your filesize is determined by total bitrate. Total bitrate is the sum of the video and audio bitrates. (30,000,000*8) / 120 seconds = 2,000,000 bits per second. That includes video and audio. 2Mbps. For audio use at most 128Kbps to leave room for video.

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