File size with various resolutions is equal

[Jay_nofilm]

I've been converting my dvr files using ffmpeg and noticed that when I change the size as the only variable, the file size remains the same.

If original size is 1024x768 and I convert to 640x360, same file size.

All the other parameters reduce the file size, video bitrate going down to -b:v 250k
and a smaller than expected file size reduction going from original 60 to -r 24
going from stereo to one audio channel reduces the size even more than I expected, I used -ac 1
with audio change, I only used that one parameter, so codec for video and audio remained same: H264 and mp4a

Not understanding the size having no affect to the file size yet, I can guess that it's stretching the pixel?

[ProWo]

Filesize=bitrate*duration

[Swedaniel]

I've been converting my dvr files using ffmpeg and noticed that when I change the size as the only variable, the file size remains the same.

If original size is 1024x768 and I convert to 640x360, same file size.

All the other parameters reduce the file size, video bitrate going down to -b:v 250k
and a smaller than expected file size reduction going from original 60 to -r 24
going from stereo to one audio channel reduces the size even more than I expected, I used -ac 1
with audio change, I only used that one parameter, so codec for video and audio remained same: H264 and mp4a

Not understanding the size having no affect to the file size yet, I can guess that it's stretching the pixel?

Maybe the video get put into the cache and just get an quick re-wrapping from there! maybe if you restart the program, clear the hdd cache, or if you can find an setting to disable/clear the cache from within the program it can help? ellse maybe the operating system have some options to clear it/change the way it operate! maybe try change cache location to an ram disk and qickly clear it after your done with an video and want new settings when using same video source that get put into the cache?

Edit: Is it acctually re-encoding the video with the new settings or is it using an source video and just adjusting the default display settings? ie. if the source video come along and it is 1920x1080 and now the re-wrapping would "change the default" display settings/meta data/aspect ratio that an video player will use to display the video?

I think i seen someone here on the forum know how to fix this in an previous thread! Ellse if you used the program for many videos it might just pick up an cached source and changing settings wont help much untill clearing cache!

Would be same thing as if your video player cache the video source, now when you play the same video again but with new settings it might play the video from the cache and now the new encoded one with the new settings might not appear with the new settings and it is easy to belive the video encoding had no effect! same solution is to clear the video player cache or disable it!

[davexnet]

Maybe the video get put into the cache and just get an quick re-wrapping from there! maybe if you restart the program, clear the hdd cache, or if you can find an setting to disable/clear the cache from within the program it can help? ellse maybe the operating system have some options to clear it/change the way it operate! maybe try change cache location to an ram disk and qickly clear it after your done with an video and want new settings when using same video source that get put into the cache?

Is that AI generated? it's bordering on gibberish

[Jay_nofilm]

...gibberish

or attempted auto language translation.

Next, I'll try starting with a larger resolution, like 1080, and then going to smaller res. Maybe better, I'll start small and re-size up with same parameters and check how much loss there is in clarity.

It's not critial, I do save a lot of space going from one gig files to somewhere between 80mb and 200, so it is working.

Of course the worst in terms of original file size is avi. I have a webcam that I can only get vlc to record to avi and it's 500mb per minute, prolly a subject for a different thread.

Wait, is the resolution actually just a setting telling the player what size to play the video file and has nothing to do with the physical parameters of the video data?

[Swedaniel]

Wait, is the resolution actually just a setting telling the player what size to play the video file and has nothing to do with the physical parameters of the video data?

I think that is an possibility allso yea, if it is an good dvr recorder it probably create an multi resolution video to be able to quickly just change the settings for the video into the meta data instead of re-encoding! ellse for me ive got same issue with basicly whatever setting i change it create same file size allso, but only when i allready used the program for one conversion, so it collect the second conversion from the cache and those videos allso allways same file size as the other one!

[davexnet]

The files resolution is a physical property, the amount of pixels that make up the picture,
Width x height

[DB83]

The only answer has already been given in reply #2.

It is a newbie fallacy (I fell for it 25 years ago) that a change of video dimensions results in a change of file size. There is a minor change, and that is all, if you change the container format from say avi to mp4 due to the length of file header.


Of course, a player reads the video resolution from the header and scales it's own window accordingly. But that same player set for 'full-screen' will play the same video full-screen irrespective of the actual video dimensions.

[Swedaniel]

Of course, a player reads the video resolution from the header and scales it's own window accordingly.

Yeah, if that is the issue then i think someone in an previous thread had an solution for this, some sort of command lines that would make sure it re-encoded an new video and not just changing settings/re-wrapping!

[_Al_]

As was stated in first response, size is not an argument for final filesize. You set bitrate and that is what you are going to get.

If testing what filesize you are going to get for what video size, or overall testing, you need to switch to constant rate factor encoding instead. Then keeping same crf you experiment with different video sizes and check what filesize you get. crf chooses a bitrate for a scenes for you.