For example, I'm trying to convert an .avi file of 818 megabytes. Then I use Miro Converter to convert to iPhone format and the resulting file is 865 megabytes.

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Is this normal? I would expect the file to be much much smaller given that it smaller in resolution and dimensions.

What gives?

2 Answers 2


The software you're using is setting the bitrate too high. It's setting the bitrate higher than that of the source, which is just bad.

Assuming the audio track is 128kbps at 88 minutes, it would be 80.5MB. That would put the original video bitrate at around 1000kbps (717.5MB). 80.5 + 717.5 = 798MB (818,000 KB is closer to 798MB, not 818MB).

Assuming the software keeps the original audio track, the new video bitrate would be about 1083kbps. 844MB (not 865MB) - 80.5MB = 763.5MB, or about 1083kbps.

So, you definitely want to go lower than 1000kbps.

Try around 700kbps on the video track, and make it variable bitrate. The video track would be about 440MB at that bitrate. I don't know what bitrate your audio is, but it'd probably be another 80-120MBs.

  • 1
    Louis is correct. The ONLY factor in video that changes the filesize is bitrate. You can have a 1080p video encoded at 100kbs that's tiny, and a video that's 160x90 encoded at 10Mbs that's huge. It has NOTHING whatsoever to do with resolution -- only bitrate.
    – Uninspired
    Apr 25, 2011 at 4:07
  • It would be wrong to say that file size has "NOTHING" to do with resolution. With two files encoded at the same bitrate with different resolutions, the one with a smaller resolution would be smaller in file size as well. Apr 25, 2011 at 4:43
  • How can that be, Ryan? If you download a file at a bitrate of 1MB/s for 10 seconds, and another one at a rate of 102.4KB/s for 10 seconds, after 10 seconds one will be 10MB and one will be 1MB. Same idea for videos. If you stream a 10 minute movie with a resolution of 480x320, at 1000kbps, after 10 minutes you will have streamed 600s*1000 bits. If you stream the same 10 minute movie with a 1920x1080 resolution, at 512kbps, after 10 minutes you will have streamed 600s*512 bits. Apr 25, 2011 at 5:07

It doesn't just change the resolution to a smaller one, but possibly the video codec to a less efficient codec, especially since iPhone cannot handle the more sophisticated variants of the h264 codec (assuming this is what the converter creates).

(If you were to reduce a PNG image by 50% in resolution but saved it as BMP, it'd likely still be larger. Similar issue.)

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