BDMV versus MP4

[yugoman1]

Hello, I know this is not a specific VS question but as I work with VS and know that some of you guys understand this stuff, I thought I would ask.....up until now I archive all of my video files....raw footage, BDMV and TS folders, but as you guys know, you need a lot of space.

A couple of days ago, a friend gave me a downloaded film called an MP4 Bluray (a 2 hour movie) The file size was 1.96 GB. When I watch it on the computer, the quality is HD quality.So I thought I would render it to a BDMV file (now 21GB) for burning a BLURAY disc, and when played on my BLURAY player, the quality is still excellent HD quality.

So the question is this.........why save all of my disc images or BDMV files etc. at 20GB or so for 2 hours of footage if we can use these MP4 files and maybe archive these ? I`m sure its not quite as simple as this but I would be interested in any comments.

[Ken Berry]

A couple of thoughts. It depends, though, on which Blu-Ray format you chose. I suspect it was the transport stream mpeg-2 one. That would account for the greatly increased file size. Like its standard def counterpart, high def mpeg-2 uses a different compression from mpeg-4 and results in larger files.

Now, on the mpeg-4 side, things get a little confusing, since it is possible to have high def mpeg-4 which uses the mp4 extension. But it is not directly Blu-Ray compatible. The mpeg-4 format which is one of the Blu-Ray acceptable formats is AVCHD which is mpeg-4 encoded with the H.264 codec and uses either .mts or .m2t as extensions (and even sometimes just plain old .mpg).

Both mp4 and AVCHD, which use much more compression than mpeg-2, will produce smaller files.

But when you ask about burning mp4 to a Blu-Ray disc, did you mean using VS and selecting Share > Create Disc > Blu-Ray then one of the sub-sets? Or did you mean -- as I suspect you might have since you mention archiving -- simply burning mp4 to a Blu-Ray disc as data files, using some other program? Then relying on a Blu-Ray player to be able to recognise the format and play it.

[yugoman1]

Hello Ken, Yes I did select Share/Create Disc/ Bluray and then untick create a disc but tick the create bluray folder.........and then I burned a disc using a different program. It is just that I take a lot of HD video for family & friends, and end up keeping the disc images (bdmv folders) which are very large, and when I saw the quality of this .mp4 file, I was quite amazed, and wondered if there was a way to render to mp4 for archiving purposes rather than bdmv ?? Hope this makes sense ?

martyn

[Ken Berry]

Well if you are only interested in archiving the mp4, then yes, go ahead. But VS is not the program you can use to do the archiving. The latter is a data file storage process while VS is a video disc production program, be it DVD or BDMV. Once you produce your mp4s, all you need is something like Windows Explorer or any other file management program to burn the files to disc as data files.

[canuck]

If all you want is to simply archive the created files then I would archive them to a external hard drive. You could then do the "archive" directly from VS to the drive and you don't even have to bother with burning.

[yugoman1]

Let me put it another way Ken.......if for instance I take a wedding video tommorow at full capture rate on my HD camcorder, then produce a project approx 2 hours long for dvd using VS . I would then keep the raw capture files and a copy of the disc image in case i wanted to come back later and burn more discs. These 2 files would probably be around 30gb in size and I wondered if there was any way of making smaller files for archiving without losing any quality ?

It is only that I have very recently looked at this MP4 file 2 hours long (size less than 2gb) and was stunned by the quality so wondered if things had moved on and I should be looking at some other file variation for archiving ?

[Ken Berry]

Did your friend tell you which program he used to produce this mp4 video? In any case, can you put the video back in the VS timeline and right click on it. Then copy ALL its Properties here, please, or post a screen grab of the Properties box. Then we will have a clearer idea of what we are talking about...

[yugoman1]

Hi ken, Don`t know how to screen print so here are the details....

F Format-MPEG-4 File
Size-2,060,046 KB
Duration-6644.311seconds

Video Type H264 High Profile video
Total Frames-159,304
Attributes-24 bits 1920 x 816
Frame Rate-23,976 frames/sec
Data Rate-2240kbps

Audio Type- MPEG AAC Audio
Total Samples-159,466,496
Attributes-24000Hz 16 Bit Stereo
Bit Rate 81Kbps

[Ken Berry]

Hmmm... I wonder which program your friend used to produce that film...? Its small size is accounted for by the very low bitrate for the video, and also by the audio format, yet it still appears to be a form of AVCHD though using a "cinematic" framerate of 24 full frames per second. I am not sure I can say much more about it as I have never used this version of the format before. Hopefully someone who has used it will jump in here.

I suppose the other question is how it looks on a big screen HDTV... The H.264 codec uses a very efficient compression algorithm, but I would still suspect that when reducing the bitrate that low -- when compared to the high def "normal" bitrate of anything between, say, 16,000 and 28,000 kbps -- that a fair amount of data from the original movie was thrown away in the compression i.e. that some quality must inevitably have been lost.

From my own perspective, it is really up to you to decide if the size/quality equation is satisfactory to your needs. My main worry would be that if you later wanted to unarchive your stored video, and use it, say, to make a new Blu-Ray movie (which would as you have found normally use a much higher bitrate and produce a much larger file), that expanding that stored video would involve the invention of new data by doubling up of existing data, and thus further loss of quality.

But as I say, hopefully someone with more experience of this particular format will be able to inject their own take on the matter.

[yugoman1]

Thanks again for your input Ken, it`s just that I am always looking for a way to Archive this stuff, but with smaller files, as you very quickly fill up a TB of External Hard drive space when you save raw footage, and disc images !