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I have a MP4 file with a lengh of 22:44. Here are the details:

Video:

width: 720 px  
height: 404 px  
data bitrate: 1022 kBit/s  
overall bitrate: 1182 kBit/s  
fps: 24
codec: H264 - MPEG4 AVC (part 10) (avc1)

Audio:

bitrate: 159 kBit/s  
stereo  
sample rate: 48 kHz
codec: MPEG AAC Audio (mp4a)

I thought I can reduce the current filesize (about 200 MB) by reducing the width and the height (420 x 236). I tried different programs: Handbrake, Format Factory, Next Video Converter and Super. The first three didn't worked as expected: Handbrake has a bug by setting the width and the height, the next two doesn't allow the fine setting of the videosize (only presets of width and height).

Super seems to be the best, but I didn't found a setting which reduces the file size. I reduced the width and the height but only got 20 MB less. Now I tried the xth setting and I still get a too high file size. I want to reduce the filesize to 100 MB or less. The ouput format should be FLV or MP4, because I need this for flowplayer.

Which settings of SUPER or which program should I use to reduce the file size? Of course the video should still be viewable.

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3 Answers 3

up vote 3 down vote accepted

File size is determined entirely by bitrate. If you want a smaller file size, you will need to reduce your bitrate. The lower the bitrate, the lower the quality of the file. So for example, so with your overall bitrate of 1,182 kb/s, for 22:44 (1,360 seconds), you'll have a file size (not including audio) of approx 1,607,520 kilobits, or about 200 MB. If you want to reduce your file size to 100 MB, you'll need to cut your bitrate in half.

The best thing to do to retain good quality is to do a 2-pass variable bitrate encoding. This scans the video for frame information on the first pass, and then uses it on the second pass to better predict pixel motion, scene changes, etc. So you get higher quality with the same file size.

With VBR, you will need to set a target bit rate and a maximum bitrate. You want your file size to be under 100 MB, so I would do a target bitrate of 500 Kb/s, with a max bitrate of 1 Mb/s. This will allow the encoding to use less space when it can, and more space when it needs to, and depending on the content of the video you should average around 500 Kb/s, giving you a file size of around 100 MB or less. If you are not happy with the quality at this bitrate, then try reducing your frame size to see if it looks any better.

Different encoding programs give you different options, for example, I don't think SUPER gives you the option of doing VBR. As a video editor, I work in Adobe and use Adobe Media Encoder, so I couldn't tell you which program works best, but any that give you those options should use the same codecs and give you very similar, if not the same, results.

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On another computer I tried the Adobe Media Encoder. I don't remember the error exactly but it was something like the framerate is not correct. Which settings do you use in the encoder? Only change the bit rate? But it's true that only the bitrate is important. I tried it with Free Video Converter and used one time the original resolution and the reduced resolution. The file size stayed the same! –  testing Nov 14 '12 at 23:17
    
Bitrate is the most important factor in file size, but not the sole determination. Consider that MP3 is a compressed format, and a lossy one at that. Different contents are susceptible to different degrees of compression and perceptual coding. –  Isaac Rabinovitch Nov 14 '12 at 23:59

Re-encoding will always deteriorate the quality, so be aware of that.

1000 kBit/s seems quite a lot for a 700x400 pixel video encoded with h.264. The ideal way to reduce size therefore would be to reduce the average bitrate rather than the pixel dimensions.

You can do this by either specifying a constant rate factor or setting a bitrate-restricted encoding mode. I don't have SUPER to try, but in Hamdbrake the rate factor can be simply set with a big slider – it's the default encoding option for x264 anyway.

Try starting with a value of 23. If you want less quality and less file size, increase the CRF vale in small steps (e.g. 25, 27, …) and check again.

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I haven't tried doing this with an MP4 but Free Video Converter from http://www.freemake.com should do the trick for you.

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Nice interface, but audio bitrate selection is a bit weird (only 240 kbps and upwards). Converting is quite fast (perhaps of the CUDA support). I got managed to reduce the file size to 108 MB (with 500 kbit bitrate). –  testing Nov 14 '12 at 23:13

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