Shortcomings of .m2t as an archive. at DVinfo.net

Don Blish · March 22nd, 2007, 10:17 AM

Like many of you, I have been saving an .m2t copy of each HDV project over the last 15 months. I had always planned to author these to Blu-Ray as BDMV projects with menus etc. Over the last week I have successfully used DVDit Pro HD to make a number of them into discs that to play in my Sony BDP-S1 player (updated to 1.55). I have found the video to be stunning viewed on a 1080 screen. What was disappointing is that several times over a one hour project, a “hard cut”, usually but not always to a still image, failed to appear cleanly. The lower third of the screen would hold the previous scene’s data for 6 to 8 frames. This never appeared in the DVDs from the same material. Those DVDs were output to a Cineform .avi as 480p and encoded with Adobe Encore 1.5.

These defects could have been the player’s error, DVDit transcoding or the Cineform file itself. After opening a test Cineform project in PremPro and hauling into it both DVDit’s .m2v transcode and the Cineform .m2t archive, I discovered the error came from the Cineform .m2t file. All I can surmise is that the 24mbps CBR bandwidth of this format will not handle hard cuts if they fall unluckily.

I believe each recorded clip in the camera starts with a complete “I frame” and updates of varying completeness extend over the next 14 frames. The constraints of a CBR output to tape apparently do not smartly deal with hard transitions that do not fall fortunately. Since this never appeared on authoring from a fresh standard definition .avi, I’ll have to do my HD authoring from .avi too. I still have .avi files for a few projects on disc. On others I’ll have to use HDlink to turn the .m2t files back to .avi, find the bad spots and repair them. That is easy if they are just stills. If they are the beginnings of video footage I’ll have to either recapture or snip the bad spot out.

David Newman · March 22nd, 2007, 12:27 PM

Agreed, remastering to M2T is only good for storage space, but not for quality, not for chroma depth, not for anything that may need to be reworked. Every decreasing disk storage costs is making AVI archiving a match more viable solution. M2T is designed as delivery format, not a mastering or archive solution. M2T for acquisition in HDV cameras works OK as the can not dramic scene changes at frame boundaries.

Don Blish · March 22nd, 2007, 02:36 PM

Thanks David, you have given this advice on more than one occasion. I and others had to see the problems "in the flesh" to appreciate it. I'll be ordering an eSATA card and external drive soon, since my internal SATA connections are spoken for. (Others: please do not suggest USB or firewire to me!)

Don Blish · March 23rd, 2007, 10:45 AM

As a footnote, I let DVDit HD Pro redo my 99 minute project directly from the original Cineform .avi. I let it encode as mpeg2, VBR, average 25mbps, with 10 as min and 40 as maximum. The result was flawless with no partial hard cuts.

This post on the Roxio site suggests using the Adobe Media Encoder and choosing VBR works and without DVDit having to transcode it. I think the key to good performance over cuts is to use VBR, not the CBR that .m2t uses.

http://forums.support.roxio.com/inde...howtopic=19414

Don Blish · March 29th, 2007, 10:53 AM

I took one of my .m2t projects that made a sloppy Blu-Ray disc (DVDit transcoded) and used HDlink to make it a Cineform intermediate .avi. The resulting file had no partial scene cuts. So that problem was from letting an application transcode directly from .m2t. As noted above, DVDit Pro HD does great from a good .avi

March 22nd, 2007, 10:17 AM	#1
Don Blish Major Player Join Date: Oct 2003 Location: Portland OR Posts: 227	Shortcomings of .m2t as an archive. Like many of you, I have been saving an .m2t copy of each HDV project over the last 15 months. I had always planned to author these to Blu-Ray as BDMV projects with menus etc. Over the last week I have successfully used DVDit Pro HD to make a number of them into discs that to play in my Sony BDP-S1 player (updated to 1.55). I have found the video to be stunning viewed on a 1080 screen. What was disappointing is that several times over a one hour project, a “hard cut”, usually but not always to a still image, failed to appear cleanly. The lower third of the screen would hold the previous scene’s data for 6 to 8 frames. This never appeared in the DVDs from the same material. Those DVDs were output to a Cineform .avi as 480p and encoded with Adobe Encore 1.5. These defects could have been the player’s error, DVDit transcoding or the Cineform file itself. After opening a test Cineform project in PremPro and hauling into it both DVDit’s .m2v transcode and the Cineform .m2t archive, I discovered the error came from the Cineform .m2t file. All I can surmise is that the 24mbps CBR bandwidth of this format will not handle hard cuts if they fall unluckily. I believe each recorded clip in the camera starts with a complete “I frame” and updates of varying completeness extend over the next 14 frames. The constraints of a CBR output to tape apparently do not smartly deal with hard transitions that do not fall fortunately. Since this never appeared on authoring from a fresh standard definition .avi, I’ll have to do my HD authoring from .avi too. I still have .avi files for a few projects on disc. On others I’ll have to use HDlink to turn the .m2t files back to .avi, find the bad spots and repair them. That is easy if they are just stills. If they are the beginnings of video footage I’ll have to either recapture or snip the bad spot out.

March 22nd, 2007, 12:27 PM	#2
David Newman CTO, CineForm Inc. Join Date: Jul 2003 Location: Cardiff-by-the-Sea, California Posts: 8,095	Agreed, remastering to M2T is only good for storage space, but not for quality, not for chroma depth, not for anything that may need to be reworked. Every decreasing disk storage costs is making AVI archiving a match more viable solution. M2T is designed as delivery format, not a mastering or archive solution. M2T for acquisition in HDV cameras works OK as the can not dramic scene changes at frame boundaries. __________________ David Newman -- web: www.gopro.com blog: cineform.blogspot.com -- twitter: twitter.com/David_Newman

March 29th, 2007, 10:53 AM	#5
Don Blish Major Player Join Date: Oct 2003 Location: Portland OR Posts: 227	Cineform absolved I took one of my .m2t projects that made a sloppy Blu-Ray disc (DVDit transcoded) and used HDlink to make it a Cineform intermediate .avi. The resulting file had no partial scene cuts. So that problem was from letting an application transcode directly from .m2t. As noted above, DVDit Pro HD does great from a good .avi

March 22nd, 2007, 02:36 PM	#3
Don Blish Major Player Join Date: Oct 2003 Location: Portland OR Posts: 227	Thanks David, you have given this advice on more than one occasion. I and others had to see the problems "in the flesh" to appreciate it. I'll be ordering an eSATA card and external drive soon, since my internal SATA connections are spoken for. (Others: please do not suggest USB or firewire to me!)

March 23rd, 2007, 10:45 AM	#4
Don Blish Major Player Join Date: Oct 2003 Location: Portland OR Posts: 227	As a footnote, I let DVDit HD Pro redo my 99 minute project directly from the original Cineform .avi. I let it encode as mpeg2, VBR, average 25mbps, with 10 as min and 40 as maximum. The result was flawless with no partial hard cuts. This post on the Roxio site suggests using the Adobe Media Encoder and choosing VBR works and without DVDit having to transcode it. I think the key to good performance over cuts is to use VBR, not the CBR that .m2t uses. http://forums.support.roxio.com/inde...howtopic=19414