H.264 output file size too big vs WMV

[bijoythulas]

Ok . i have been trying to convert some of my mpeg2 videos to h.264 because of the claim that

1. it reduces the size of the output file for a given bit rate/fps/size significantly.
2. youtube handles the codec better than wmv

so to experiment i converted my 1.30 min video to h.264 and the video size comes to 21 meg(bit rate 2100).

its greater than my earlier generated wmv file size which came to 15 meg (same bit rate/fps/size)

tools used megui and xvid4psp.

i would be interested in knowing what is average file size we can expect for a 1 minute video using h.264 compression (25 fps, 320x240 ,bitrate 2000).

also any links comparing the compression capabilities of various codecs.

[guns1inger]

If you use a constant bitrate, your file size will be predictable and constant. If you use two different codecs on the same clip, and use the same bitrates for audio and video, the file sizes will be the same (give or a take a small amount). The resolution doesn't come into it at all. A 60 second clip with a resolution of 720 x 576 encoded at 2000 kbps (no audio) will be the same size as 60 second clip with a resolution of 320 x 240 encoded at 2000 kbps (assuming you don't flood the encoder, of course).

[jagabo]

file size = bitrate * running time

If you want a smaller file use a lower bitrate. 2000 kbps is pretty high for a 320x240 video.

[jman98]

I'd guess that you are using variable bit rate if you're seeing that much difference in size. It's impossible to predict final size with variable bit rate but if you have a lot of experience and can set minimum, maximum and average bit rates for the encoder to use, you can have a good idea of what your final size will be if you know what you are doing.

[bijoythulas]

hi guys thanks for the response.

i still have a few questions left.

so does it mean that a h.264 video at a given bit rate is better quality than say a wmv video at the same bit rate ??.

also any idea how you set constant bit rate using MEGUI encoder.

[jagabo]

so does it mean that a h.264 video at a given bit rate is better quality than say a wmv video at the same bit rate ??.

I think that's debatable.

also any idea how you set constant bit rate using MEGUI encoder.

I don't know MEGUI so I can't answer that. But in general, 2-pass (or more) variable bitrate encoding will give you better quality than CBR and still get you the desired file size (except under certain circumstances where you ask for a high bitrate and the source just doesn't have enough detail). The down side is that it takes twice (or more) as long.

I usually don't care about the exact file size and use constant quality encoding (I pick the quality, the file turns out whatever size is necessary to deliver that quality).