M4v Aspect Ratio Video Dimension Muddle

[Greg2041]

Hi, I am a newbie to this website and I fear will have loads of questions about conversions.

My first one is this.

I have an M4V file which in Itunes says its Video Dimension is 853 x 478.

I have checked Media Info separately and its reads 640 x 478. Why the difference?

When I play the files on Quicktime, WMP 12, VLC etc, the file images are fine but when I download this file onto a memory stick and watch it on my LG TV, the movie looks almost square, the actors stretched and unfortunately, even using the hardware, on the TV nothing changes.

What, in your considered opinion, is the problem?

BTW All other downloads from various sources, work fine.

Help!



Greg

[jagabo]

It probably uses a frame size of 640x478 but with non-square pixels to give a display aspect ratio of 16:9. Itunes is showing you the size it will be after stretching the width to 16:9 DAR. Does MediaInfo report the DAR as 16:9?

[Cornucopia]

iTunes is based on Quicktime. Quicktime is notorious for mis-reporting dimensions. All they would have to do would be to say "equivalent squarepixel dimensions:..." along with "stored dimensions" and "display aspect ratio", and they would avoid all the confusion.

Moving on, does the video look squarish when played on your TV (via USB stick, etc)? It could be that the LG player app doesn't support the DAR flag, or it could be that jagabo's hint of the file not having it's DAR stored at all is messing it up.

640x478? That is so weird that 2 lines would have been removed from a common 640x480 format...

What was the source for this file?

Scott

[vhelp]

i'm not familiar with m4v format, so i don't know if there is an aspect ratio flag or not in there.

you could also try the command line, ffmpeg.

ffmpeg -i video.m4v

and read the results. it should tell you the real pixel dimensions as well.

[jagabo]

i'm not familiar with m4v format

As I understand it, both are the MP4 container. But the M4V extension is used when there's AC3 audio inside. So, yes, the container supports aspect ratio flags.

[Cornucopia]

It was my understanding that M4v & M4a were MPEG4 elementary streams, like M2v & M2a for MPEG2 and M1v & M1a for MPEG1. Using "M4v" for a container format would certainly go against their longstanding habit. But whatever...

Scott

[vhelp]

it just occured to me.. the op is using itunes! that indicates these are d/l's and he might be on a mac ?

[Greg2041]

It probably uses a frame size of 640x478 but with non-square pixels to give a display aspect ratio of 16:9. Itunes is showing you the size it will be after stretching the width to 16:9 DAR. Does MediaInfo report the DAR as 16:9?

Back again. A Mac? What? No, I have a proper computer. Actually, I can't afford a Mac!

Yes, Media info shows the DAR as 16:9. The LG TV is a M2450D. I need to see whether it supports DAR. I would have thought they all did but I'm probably wrong and that would explain it.

The original source is ITunes where the movie is a free download.

So does WMP, VLC etc all stretch the width? Bit confused. Isn't 640x478 16:9? Media info shows this as 640*478 (16:9)

[jagabo]

640/478 ~= 1.34 ~= 4:3

[vhelp]

you said itunes display 853x478 which ~= 16:9 ..that's why i suggested ffmpeg. unless the file was itunes encoded. doesn't apple use the atom signature? post a hex dump screenshot of the file using a hex editor. or use virtualdub's, under tools.

if the file is not too big, 30mb or less, post that, i'm sure a better determination can be made, otherwise post a hex dump screen shot. the dump will show whether its an apple itunes encoded video (atom) versus an mp4 avi riff.

[Greg2041]

Getting a bit complicated now. Hex dumps and Atoms sounds more like science fiction. Leave that with me to muddle through and google. BTW what is an Atom Signature?

The file is definitely an official proper Apple file though. It is a freebie from ITunes if that helps.

Thanks again...

Greg

Ps I will download the programs and let you know what I find.

[Greg2041]

Okay there are a lot of numbers in the Hex dump. How do I copy and paste it? Which part is most useful to you?

[vhelp]

it is an avi riff  -- if you see similar to this:  RIFFZ...AVI LIST
it is an moov atom -- if you see similar to this:  ... ftypM4aA ...

[Cornucopia]

Instead of telling us what MediaInfo shows, why don't you just post the MediaInfo text? That can clear up some of this.

Scott

[Greg2041]

Thanks Vhelp. It shows ftypM4aA.

Cornucopia. You mentioned about a possibility of a lack DRA on my LG TV. Well, I tried the file on my parent's Samsung TV and it was absolutely fine. I have since learnt of other customers who have complained that DRA is missing on their LG TVs. Maybe that's the problem? Is there an easy fix? I'm guessing not.

Media Info shows:

Format : MPEG-4
CodecID : M4V
FileSize/String : 39.1 MiB
Duration/String : 2mn 34s
OverallBitRate/String : 2 124 Kbps
Movie : Mini Adventures of Winnie the Pooh: Pooh's Game
Performer : Rick Reinert
Genre : Kids & Family
Recorded_Date : UTC 2011-10-07 07:00:00
Encoded_Date : UTC 2012-01-19 22:32:10
Tagged_Date : UTC 2012-01-19 22:32:11
Copyright : © 1983 Disney
Cover : Yes
cnID : 496699620
atID : 496699621
geID : 4410
sfID : 143441
desc : Pooh, Rabbit, Piglet and Roo are gathered on the old wooden bridge to race sticks in the river below. The first stick to pass under the bridge will be the winner. Soon the race is on, and Piglet is sure his long, grayish stick is leading the pack — until
stik : 9
purd : 2013-04-02 21:13:58
xid : buenavista:vendor_id:NKQA4466WDSHE
flvr : 4:640x480LC-128
iTunEXTC : mpaa|G|100|
ldes : Pooh, Rabbit, Piglet and Roo are gathered on the old wooden bridge to race sticks in the river below. The first stick to pass under the bridge will be the winner. Soon the race is on, and Piglet is sure his long, grayish stick is leading the pack — until that "stick" turns out to be Eeyore!
iTunMOVI : <?xml version="1.0" encoding="UTF-8"?> / <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> / <plist version="1.0"> / <dict> / <key>asset-info</key> / <dict> / <key>file-size</key> / <integer>40950133</integer> / <key>flavor</key> / <string>4:640x480LC-128</string> / <key>screen-format</key> / <string>widescreen</string> / <key>soundtrack</key> / <string>DD,DS</string> / </dict> / <key>cast</key> / <array> / <dict> / <key>adamId</key> / <integer>6841988</integer> / <key>name</key> / <string>Jim Cummings</string> / </dict> / <dict> / <key>adamId</key> / <integer>59580566</integer> / <key>name</key> / <string>John Cleese</string> / </dict> / <dict> / <key>adamId</key> / <integer>188907444</integer> / <key>name</key> / <string>Tom Kenny</string> / </dict> / <dict> / <key>adamId</key> / <integer>427283577</integer> / <key>name</key> / <string>Bud Luckey</string> / </dict> / <dict> / <key>adamId</key> / <integer>496320158</integer> / <key>name</key> / <string>Wyatt Hall</string> / </dict> / <dict> / <key>adamId</key> / <integer>467998058</integer> / <key>name</key> / <string>Travis Oates</string> / </dict> / </array> / <key>codirectors</key> / <array/> / <key>copy-warning</key> / <string>FBI ANTI-PIRACY WARNING: UNAUTHORIZED COPYING IS PUNISHABLE UNDER FEDERAL LAW.</string> / <key>directors</key> / <array> / <dict> / <key>adamId</key> / <integer>496699621</integer> / <key>name</key> / <string>Rick Reinert</string> / </dict> / </array> / <key>producers</key> / <array/> / <key>screenwriters</key> / <array> / <dict> / <key>adamId</key> / <integer>2037174</integer> / <key>name</key> / <string>A. A. Milne</string> / </dict> / </array> / <key>studio</key> / <string>Disney Junior</string> / </dict> / </plist>
Video
ID/String : 1
Format : AVC
Format/Info : Advanced Video Codec
Format_Profile : Baseline@L3.0
Format_Settings_CABAC/String : No
Format_Settings_RefFrames/String : 1 frame
CodecID : avc1
CodecID/Info : Advanced Video Coding
Duration/String : 2mn 34s
BitRate/String : 1 556 Kbps
Width/String : 640 pixels
Height/String : 478 pixels
DisplayAspectRatio/String : 16:9
FrameRate_Mode/String : Constant
FrameRate/String : 23.976 fps
ColorSpace : YUV
ChromaSubsampling : 4:2:0
BitDepth/String : 8 bits
ScanType/String : Progressive
Bits-(Pixel*Frame) : 0.212
StreamSize/String : 28.6 MiB (73%)
Language/String : English
Encoded_Date : UTC 2012-01-19 22:32:10
Tagged_Date : UTC 2012-01-19 22:32:11
Color primaries : BT.601 NTSC
Transfer characteristics : BT.709
Matrix coefficients : BT.601

[jagabo]

Since you LG TV doesn't support aspect ratio flags you'll have to resize to square pixel and reencode.

Or get a decent standalone media player. It will obey aspect ratio flags and play a much wider array of containers and codecs.

[vhelp]

i was going to suggest to transcode to another container (via ffmpeg) and set the dar flag in that step. but if it is hardware problem then that may not help.

[Greg2041]

Yup. I thought that might be the case. Just from a layman's point of view. Apple's pixels are rectangular then?

Seems strange. Are they superior to square pixels?

Thanks vhelp, I am guessing that there must be some sort of Flag there, as all is well on the Samsung TV so it must be a hardware problem.

Solution - Don't buy an LG TV!

Now, I must head over to the subtitles area where our paths may cross again. Blasted iTunes subs (closed captions) only work with quick player. Now I need to work out how to abstract them to an srt file for my parents TV. Dad has severe hearing problems.

Thanks again guys!

Greg

[jagabo]

Apple's pixels are rectangular then?

In that particular video, yes.

Seems strange. Are they superior to square pixels?

It depends on your source. Any time you resize a digital frame you get some loss of quality. If your source is square pixel keeping it that way will avoid quality loss from scaling. On the other hand, DVD uses non-square pixels. So retaining the original frame size and using AR flags lets you avoid quality losses from scaling to square pixels.

[Greg2041]

Very interesting. Thank you.

Greg

[Greg2041]

Since you LG TV doesn't support aspect ratio flags you'll have to resize to square pixel and reencode.

Or get a decent standalone media player. It will obey aspect ratio flags and play a much wider array of containers and codecs.

Out of interest how to do you re-encode to change the aspect ratio? I tried it in Handbrake as a test but nothing changed. What would you use?

Saw Megui but that looks a bit complicated.

[jagabo]

I would use AviSynth and the x264 encoder. But that's probably more than you want to learn just for resizing to square pixel. I don't really use Handbrake but it seems to try really hard to prevent you from changing aspect ratio settings. Xmedia Recode has a similar GUI and allows you to change the frame size and AR.

[Greg2041]

Thanks Matey. I will give it a go.



Greg

[Greg2041]

Works perfectly. Brilliant!

Greg

[jagabo]

Glad it worked out.