G-Spot says its 4:3, but its really 16:9

[Toastie]

I have an NTSC mpeg-2 video clip that was recorded by an Canon digital video camera. It is recorded in .mod format, which is a container, essesntially like mpeg-2. I can use MPEGStreamClip to convert it to an actual .mpg, mpeg-2 container.

This video is shot in 16:9 format and the .mod file plays back properly on my computer with VLC as 16:9, yet when I check, G-Spot says its 4:3. There definitely is some info in the header that says it 4:3, so how the heck does VLC know to play it back properly as 16:9 ?? I am very puzzled by this.

Here is the screen cap from G-Spot saying the .mod file is 4:3:



and here is a screen cap from VLC playing back that same file as 16:9, which is how it should look:



When I try to do a re-encode it comes out all squished side to as 4:3. Obviouly the encoder is paying attention to the info in the file header that says its 4:3. I can easily correct for this by using DVDPatcher to make a change in the file header before the re-encode takes place to say it 16:9. Problem solved.

My question is if original file has the wrong info in it out of the camera - how in the world is VLC able to tell its 16:9 and correct for that on playback?? What is VLC seeing that the encoder and G-spot are not?


Thanks!

[chowmein]

That looks 4:3 letterboxed to me? Not sure (I am PAL land). What camera is it? Are you sure it shoots 16:9 anamorphic?

[Toastie]

Thanks for your reply, but I don't think that is it. Here is a picture of what it looks like when I first open this in VLC without going to full screen mode:


And this is what the picture looks like when I use the "snapshot" funtion within VLC for that same exact frame of the video - no black bars (853/480 = 1.777, same as 16:9):

[aedipuss]

try mediainfo in text mode. paste results here.

[Toastie]

Mediainfo says it's 16:9 - so why does Gspot say 4:3 ?


General
CompleteName : D:\MOV001.MOD
Format : MPEG-PS
FileSize/String : 2.63 GiB
Duration/String : 1h 19mn
OverallBitRate/String : 4 762 Kbps
Video
ID/String : 224 (0xE0)
Format : MPEG Video
Format_Version : Version 2
Format_Profile : Main@Main
Format_Settings_BVOP/String : Yes
Format_Settings_Matrix/String : Custom
Format_Settings_GOP : M=3, N=15
Duration/String : 1h 19mn
BitRate_Mode/String : Variable
BitRate/String : 4 411 Kbps
BitRate_Maximum/String : 9 600 Kbps
Width/String : 720 pixels
Height/String : 480 pixels
DisplayAspectRatio/String : 16:9
FrameRate/String : 29.970 fps
Standard : NTSC
ColorSpace : YUV
ChromaSubsampling : 4:2:0
BitDepth/String : 8 bits
ScanType/String : Interlaced
ScanOrder/String : Top Field First
Compression_Mode/String : Lossy
Bits-(Pixel*Frame) : 0.426
StreamSize/String : 2.44 GiB (93%)
Audio
ID/String : 189 (0xBD)-128 (0x80)
Format : AC-3
Format/Info : Audio Coding 3
Format_Settings_ModeExtension : CM (complete main)
MuxingMode : DVD-Video
Duration/String : 1h 19mn
BitRate_Mode/String : Constant
BitRate/String : 256 Kbps
Channel(s)/String : 2 channels
ChannelPositions : Front: L R
SamplingRate/String : 48.0 KHz
BitDepth/String : 16 bits
Compression_Mode/String : Lossy
Video_Delay/String : -66ms
StreamSize/String : 145 MiB (5%)
Menu

[Toastie]

I should add that if I use DGindex to create an index file of this video, the .d2v file says 4:3 when I look at it with notepad.

Of course I am able to change the 4:3 info in the header with DVDpatcher, and index again with DGindex to get a correct d2v file so my re-encode comes out ok.

So I know how to resolve the problem, by what the heck is goiing on here??

[aedipuss]

don't blame the software for the shortcomings of your weird ass camera. blame the moron who decided to put standard dvd spec mpeg-2 ps in a mod container instead of the correct mpeg container.

[Toastie]

I am not "blaming" the software, just asking a question. I can use MpegStreamClip to read the .mod file and export a .mpg but the situation is the same.

If it says 4:3 in the header, how is it possible for mediainfo to say 16:9 or VLC to know to play it back as 16:9? Where else would they be getting that from?

[jagabo]

MPEG files have more than one header.

[sambat]

http://en.wikipedia.org/wiki/MOD_and_TOD

The last paragraph of the first (Overview) section comments on the AR dilemma and how MediaInfo reports it correctly.

[Toastie]

Thanks! Wikipedia says: "Some tools such as MediaInfo can correctly report the aspect ratio of widescreen MOD files, but media players may or may not display them correctly depending on the capabilities of the video decoder that they are utilizing at the time."

So its really the codec that is not reading file correctly.

[jagabo]

I happen to have a .MOD file in my collection of odds and ends. GSpot reports the aspect ratio is flagged as 4:3. But it also shows the video has a sequence_display_extension that indicates the flagged 4:3 picture is contained in a 540x480 sub portion of the 720x480 frame. That means the full 720x480 frame contains a 16:9 video (1.333 * 720 / 540 = 1.778). So GSpot is partially correct. The pixel aspect ratio should be reported as 32:27, not 8:9.

[Alex_ander]

Here is the detailed explanation of how sequence_display_extension is used with mod files:
http://www.dvmp.co.uk/mod-video-file-format.htm

In usual commercial DVD's the sequence_display_extension can usually be found for pan&scan option, and in my experience, it is not read by a DVD player in other cases (if present). So the workaround with DVDPatcher is OK before usage of those mpegs for authoring, but is not enough to modify an already authored DVD (setting the AR in ifo's is necessary for hardware playback, while mpeg AR correction is not).

[VirtualDoobMon]

If your files are MOD try using SDCOPY to back them up. Google Sdcopy.zip and i think you will find it on megaupload/mediafire. It will import your files and set the 16/9 flag as well as rename to .MPG

[jagabo]

SDCopy will set the MPEG aspect ratio flag to 16:9 but it doesn't change the sequence_display_extension so the resulting MPG file will be mal-formed. A device that plays it "properly" will show the video as 2.37:1 instead of 1.78:1. I would use it only as a last resort -- where you can't get your editor or player to display the original video as 16:9. What you're doing is modifying your MOD file to incorrect settings in order to make up for a deficiency in your editor/player.

All the players I've tried play MOD files with the correct display aspect ratio. WMP, MPCHC, VLC.

[Toastie]

I think I see whats going on now.

Resetting the DAR to 16:9 first and then reencoding gives good results. The file is flagged as 16:9, the par is 32:27, and no more sequence_display_extension nonsence.

If I am not going to reencode, and I just author with TMPG DVDAuthor the dvd plays properly. But but if I then check an individual VOB with Gspot the sequence_display_extension is still there and its set to 720x480. Double clicking on that VOB it plays in VLC, but is squished side to side. If I am not going to reencode, an easy approach to just clean things up is to first demux, use Restream to set the .m2v to 16:9 and also delete the sequence_display_extension, remux, and then author. That sequence_display_extension is something that isn't necessary and just causes confusion.

Thanks for all the comments!

[Alex_ander]

the sequence_display_extension is still there and its set to 720x480

This only means it keeps the extension, but resets it to default, which must work the same as without it. By the mpeg2 standard, if that extention is present, the devices that use it, apply the AR flag with reference to numbers written in it (instead of taking those numbers from resolution). If the numbers in the extension coincide with resolution numbers, any device will give the same image proportion. So it's not necessary to delete the extension. Another known program that writes a default extension (even if not present in source) is DVDRemake. But most hardware players seem to not use it at all (even pan&scan can work without it, just by taking that mode from ifo's).

[Toastie]

TMPG DVDAuthor 1.6 does not write a default extension even if not present in source. It writes it if it is present in the source, and gives individual .vob files a different extension (720x480 vs. 540x480 in the source) if the header in the source file has been altered from 4:3 to 16:9, with the extension left at 540x480

TMPG DVDAuthor 1.6 is the older version that does not include an encoder - all it does is author.

[Alex_ander]

OK, then it's more safe to remove it.