question about rendered mp4 file sizes

drw wrote on 9/15/2013, 12:32 AM
I have a short video of my daughter at a piano recital that I shot with a Canon HD camera. The source file is 1280x720 29.97fps progressive MP4 format with 48k stereo audio, and is about 75M in size. I've edited it just a little, cut a few seconds out of the start and end, and added fade in/out. When I try to render this to a similar MP4 format, I end up with file sizes that are over 160M. I tried a couple different ones, like sony tablet 720p, and internet 1280x720 30p, and they were both huge compared to the original. Why are these rendered files so much bigger than the original? The video is about 3 1/2 minutes long, and the edited portion is about 4 seconds total, so the rendered version is almost identical to the original. Is there some other format I haven't found yet that would be closer in size to the original?

Comments

Steve Grisetti wrote on 9/15/2013, 8:22 AM
Well, MP4s are compressed using a couple of techniques, so it's rare to find two MP4s that are exactly the same size unless, by some miracle, you are using exactly the same specs as the original video include frame rate, i-frames, bit rate, compression level, etc.

The video in your camcorder is compressed so that it is the optimum size for storage in a camcorder. Your output is optimized for whatever template you selected.

Instead of focusing on the size of your output video, consider instead how you plan to use the finished video. Is it for upload to YouTube? For output to a DVD or BluRay? For use in another video project? There is an optimized template for each purpose.
musicvid10 wrote on 9/15/2013, 9:57 AM
"When I try to render this to a similar MP4 format, "

We don't know what that is. "Similar MP4 format" doesn't show up under any Vegas render templates or settings.

Post COMPLETE MediaInfo properties for both your original and rendered files and it should be painlessly simple to determine what you've done. MediaInfo is a free download from Sourceforge.
drw wrote on 9/15/2013, 11:01 AM

When I said "similar" in my first post I meant that I matched a 1280x720, 29.97fps, AVC MPEG-4 source file to a rendered format with those same parameters. When I look in the two HTML files they do look very similar, same codec, etc. but the primary difference is the bit rates, they're way different, and that's what's causing the big difference. Thanks to Mediainfo I now know the bit rate my camera produces for each file, so that clears up the mystery.

Not that I need any particular file size, i was just wondering how they could be so different, but I didn't know the bitrate of my camcorder, otherwise I would have figured it out sooner.

thanks for the Mediainfo pointer, that was a big help.


Chienworks wrote on 9/15/2013, 11:48 AM
It's all about the bitrate. That's what matters, and i haven't seen you mention that anywhere. The size of the output file is determined by two factors: the length, and the bitrate. Assuming your output length is pretty much the same as the original file, the size difference is caused by different bitrates used when rendering. And ... that's all there is to it.

If you want a smaller file, use a lower bitrate.