Video File Size

[seekermeister]

After downloading quite a few videos...usually 720x720, I have noticed that when I download a file that is 640x640, that it is somwhat larger than the one with the higher resolution. It would seem that it should be just the opposite, since the higher one has to cover more screen area. Can someone explain why this is?

 

[mickey megabyte]

you're ignoring compression, and possibly frame-rate and length of movie.

the 720 video obviously has had more compression applied to reduce its file size (or is using a more efficient codec) compared to the 640.

and you don't mention how long these clips are - a two hour movie is obviously going to contain more frames (and hence data) than one lasting half-an-hour.

 

[seekermeister]

Film length is not a factor, because it will be the exact same film in both resolutions. As far as the compression, etc. I have no idea, but it would seem that if a larger resolution can be compressed to a particular size, the smaller resolution could be compressed to at least the same size or smaller. However, it is obvious that there is something that is not as it would seem...at least to me.

 

[mickey megabyte]

Film length is not a factor, because it will be the exact same film in both resolutions. As far as the compression, etc. I have no idea, but it would seem that if a larger resolution can be compressed to a particular size, the smaller resolution could be compressed to at least the same size or smaller. However, it is obvious that there is something that is not as it would seem...at least to me.

if the 640 film was compressed using the same codec and the same bit-rate, then yes, it will be made smaller than the 720 one.

i guess it comes down to whoever produced the videos in the first place, and their personal choice of codec and compression settings. also the quality of the source material is important - it's a lot easier to compress 'clean' images compared to grainy or dirty ones.

it's a bit like asking why a 3 minute wav file is bigger than a 6 minute mp3 file.

 

[seekermeister]

The files that I'm talking about are all .FLVs, so wouldn't they all use the same codec? They are also all from the same source, so it's not a matter of just the different people do different thing...I think.

 

[mickey megabyte]

flv is not a codec - neither are avi, mkv etc etc

they are containers and can be encoded with various codecs - you can take a movie, compress it using a divx codec (for example) and then turn it into an avi or mkv or whatever you like.

flv's can be produced using a variety of codecs - including sorenson spark, on2 vp6, screen video, screen video 2 or h264, depending on the software being used. each of them will yield different results, with differing file sizes.

you can even chose different compression settings within the same codec, if you wished - so you can take the same source, and produce two flv's from it, both using h264 codec, but with different compression settings.

it's a bit like jpg images - they can have variable compression applied to them. for example, here the big picture is actually a smaller file size as it has been more heavily compressed.

100x100 pixels, file size 6.4 kB
150x150 pixels, file size 2.8 kB