avi to mp4 video sizing

[rage777]

this may have started after an update, but when i convert an avi to mp4 and either leave the original video size or customize it, it turns out to be a different size all together. i have never had this problem before. could it be a particular avi?

[rumplestiltskin]

Which app is doing the conversion?

[rage777]

oh yeah. i guess that would help. i'm using ffmpegx vers. 0.0.9y for mac. when i usually convert the videos i make them bigger than the original. now they end up being a weird size about 4:3 instead of widescreen dimensions.

[terryj]

if they were originally 16:9 and then are being converted to 4:3,
then there is a setting in ffmpegx's Video conversion tab that isn't set properly.
Check the "Autosize" selection in the Video Tab.

[Case]

Please talk specifics (target video codec, size, used preset, settings), so others can verify the behavior on their system.
Is the weird size in a Mac software player like QuickTime Player, or on a handheld device like iPod Video (or both)?
The online manuals [1,2,3] have a few things to say about restrictions to video size.

[rage777]

i keep the ratio the same, just change the video size keeping proportion constraints. if the original is 2.35:1 i use autosize to keep the ratio correct. i am using quicktime to playback the videos and also use them on my ipod.

[rumplestiltskin]

Okay; iPod use.

Do whatever math is needed to keep the frame size at 640 pixels wide (or less). Frankly, enlarging the frame size won't improve your viewing quality.

ffmpegX conversions to mp4 or h264 should adhere to the "rule of 16's" so let's say your source video is (for whatever reason) 588 x 268. You'd like to view this on your Mac and in your iPod so let's do some math here:

588 is not evenly divisible by 16 so we need to fix this first. 576 -is- evenly divisible by 16 so let's use that as the target width.

576 / 588 = .9796

Now let's multiply the height by .9796.

268 x .9796 = 262 pixels (rounded up).

262 pixels isn't evenly divisible by 16 so let's look at two numbers (close to 262) that are: 256 and 272. 262 is only 6 pixels taller than 256 but is 10 pixels shorter than 272 so let's choose 256 as it's closer. Now we're done.

576 x 256 is a good "legal" width and height for ffmpegX to convert. If you're looking to maximize quality (and are using the H264 setting), drop the Qmin to 5 and Qmax to 30.

Bottom line: Set your desired frame size -manually- rather than rely upon ffmpegX to do it for you. Use H264 (640x) even if you don't enlarge the frame. Stick to the "rule of 16's". Tweak the Qmin/Qmax settings if desired.

Let us know if this helps.

[rage777]

well, for some reason the height stays the same but the width is what changes. i had an avi that was 624 x 336 that ended up i think 448 x 336. is there a way to revert to an earlier software version? i think that this all started with the update.