Change Aspect Ratio of .mp4 without re-encoding

[rtharagan]

I have a bunch of downloaded .mp4 files that, for some reason, are in 16:9 format while the original material was in 4:3. I want to put these on an Zune, and the Zune can't stretch video. So I'm looking for a way to change it, but re-encoding is out of the question. Thanks.

[poisondeathray]

mp4box (yamb is the gui)

you can set the par value

[PuzZLeR]

Other than basic stuff, YAMB can be buggy when it comes to more complex items, such as PAR... (PAR = Pixel Aspect Ratio). Well, it has been for me at least.

I prefer the the mp4box CLI using the "par" command for this. Look here for some documentation:
http://gpac.sourceforge.net/doc_mp4box.php

Either way, this will be done at the container level, not on the stream itself.

However, I'm just curious, doesn't the Zune only support square pixels (PAR=1:1)? Even if you could adjust the PAR value, it probably would be ignored anyway.

As well, are your source MP4 files square pixel 16:9, something like 640x352 with PAR 1:1? This changes things.

[rtharagan]

Thanks for the helpful replies. Where is PAR in the gui? I would just use the CLI like Puzzler said, but when I double click the exe, it comes up for 1/10 of a second and then disappears. Don't know why. And about the Zune and square pixels, I'm not sure, actually I have no idea, but I think it's worth a try.

[poisondeathray]

mp4box is a command line application, you can't just double click it

in yamb, create a new .mp4, highlight the video track, hit properties button, select pixel aspect ratio

[rtharagan]

Okay, I've never used a command line interface before, so sorry if I'm sounding stupid, but here is what I type in:

mp4box -add inputfile.mp4#video -par (don't know)=4:3 -add inputfile.mp4#audio -new newfilename

I think I'm getting everything right except for the PAR command because it successfully imports the audio and video tracks, but what is the TrackID? Because the documentation says the command is: -par trackID=PAR.

So basically, what is the TrackID? Thanks for your patience.

[poisondeathray]

track should be 1 for the video, 2 for the audio

you have to calculate the par

display aspect ratio = frame aspect ratio x pixel aspect ratio

e.g. NTSC spec DVD 720w 480h frame size, you want it to display 16/9

16/9 = 720/480 x 32/27

so the calculated par is 32:27

mp4box -add inputfile.mp4#1ar=X:Y -add inputfile.mp4#2 output.mp4

where X:Y is the par value

As puzzler mentioned, this is container level signalling, while most software players will acknowledge the flag, I doubt it will work on your device. Please post if it works or not for the zune, so others searching for this can benefit

[rtharagan]

IT WORKS!! Thank you SO much poisondeathray and puzzler for your quick replies. Yah, put it on the Zune, displays in perfect, flawless, 4:3!! So that's great to know.

[PuzZLeR]

[ronnylov]

track should be 1 for the video, 2 for the audio

you have to calculate the par

display aspect ratio = frame aspect ratio x pixel aspect ratio

e.g. NTSC spec DVD 720w 480h frame size, you want it to display 16/9

16/9 = 720/480 x 32/27

so the calculated par is 32:27

mp4box -add inputfile.mp4#1ar=X:Y -add inputfile.mp4#2 output.mp4

where X:Y is the par value

As puzzler mentioned, this is container level signalling, while most software players will acknowledge the flag, I doubt it will work on your device. Please post if it works or not for the zune, so others searching for this can benefit

Wait a minute here. 16:9 NTSC DVD at 720x480 has a pixel aspect ratio of 40/33. So 32/27 is wrong. The 16:9 DVD picture is stored in 704x480 and then some padding is added to get 720x480 DVD.