Why do we need MJPEG?

[Main]

Hi,

I guess this is kind of a stupid question and most likely very out of date but I hope some one could tell me what are the advantages of MJPEG over MPEG 2?

Thanks

[ktnwin]

Let me try:
1) JPEG is the compression format for still picture (like digital camero produces today)
2) motion vide (for NTSC) is 29.99 frames per second, that means there are almost 30 still pictures per second
3) each of those get compressed in JPEG format
4) the serie of those JPEG pictures stringed together is called MJPEG (motion JPEG).
This is my plain guess, if I am wrong, please educate me.

[ktnwin]

I forgot to say what the advantages of each:
1) MJPEG advantage: each still picture is compressed independently, so the compression is faster (???) then MPEG. The downside is the size of the output file, still huge
2) MPEG compression on the contrary is based on the differences between the still pictures (frames). In typical movie, there are pretty little motion, therefore the delta is small. MPEG compression normall takes longer to perform in software but produces much smaller file size.
The main advantage of MPEG is stand alone players (VCD, DVD) can play them. None plays MJPEG (this must comes from the Studio DC-10 capture card !!!).

[Gazorgan]

MJPEG can be 'virtually lossless'. Example: Capturing vidoe at 640x480 with 44 Khz PCM stereo sound, in HuffyUV codec ( alossless codec)I get around 14 GB/hour (off the top of my head). That's on the ragged edge of my larger capture drive to not drop frames. RGB capture is something like 4 times more data. Easily 30-40 GB/hour( again, off the top of my head, could be higher).

Enter MJPEG. It has loss. But, if you set the quality to 90%-95%, it is 'virtually lossless'. That is you can take that 40 GB RGB capture, the 14 GB HuffyUV capture, and get a 9-11 GB capture.

Virtually the same quality. You can lower the quality down to 80% or 85% to save space or work with slower harddrives. The lower the quality setting, the more artifacts that will show up in the video, and in turn the final product.

MJPEG is for capturing, or working with raw video where you don't want to include codec artifacts and loss. You don't use it as a final product, just capture, or as an intermediary format. You could output MJPEG from Adobe Premiere, and encode the final product in TM or VDUB as normal.

Hope that helps

[Main]

Thanks for the help. Please correct me if I'm wrong - MJPEG is better picture quality than MPEG (at least at 100% quality). But does 100% quality, no frames droped, both frames, full screen mean anything? That is, isn't it different for different capture cards? So, how is "loss less" defined? When a capture card says "SVHS quality", what would happen if I use Betacam as my source?

I know I have a lot of questions, but thanks for your help.

[rick6612]

Hi Main,

The difference between MJPEG and MPEG doesn't really have much to do with picture quality. Hi bit rate MPEG2 can be very high quality. My RT2500 can capture MPEG2 at up to 25 Mb/s, which gives a very high quality picture.

In terms of video capture, the main differences between MJPEG and MPEG2 is that MPEG2 takes a lot more processing power to encode and thus is harder to do in "real time." With the fast processors that are available today, it is more realistic to expect to be able to encode MPEG2 in real time while capturing video. But it wasn't long ago that processors just weren't fast enough to encode MPEG2 in real time. That's why MJPEG was popular for inexpensive video capture devices.

In terms of video editing, MJPEG is better suited to editing because each frame in an MJPEG .avi file is a separate entity. As a previous message in this thread indicated, MPEG typically uses a process where the only information saved for most frames is just the data that is different from the previous frame. This makes editing more difficult because you don't actually have direct access to each individual frame. This also creates a situation where you can end up having to re-render your video frequently while editing.

In terms of storing video, MPEG gives better compression, so you can fit more video of the same overall picture quality in a given amount of space than you can with MJPEG. This is especially desirable when you are trying to fit a feature length movie on a DVD, for example.

[Sulik]

MJPEG is basically I-frame only MPEG (no temporal compression).

[Main]

Thnks for your help. It was helpful.

So, can you please tell me where DV format comes in? I mean, if I download video through a firewire connection, what is the qualit I get? Is this compressed? Sorry if I sound stupid, but compared to MPEG2 and MJPEG where does it stand? It can be edited real time on the PC, can't it? Since there is no generation loss why can't this be a solution for Brodcast editing? Shoot on a Digital Pro Camera, download through firewire and edit on a PC, then take the edited video through the firewire back on a Digital camera or VCR for broadcasting?

Thanks

Thanks

[rick6612]

DV is compressed, and there is some amount of loss due to the compression. DV is probably more like MJPEG, in that it contains separate individual frames, as opposed to the typical MPEG video which does not.

One of the main advantages of the whole DV format is that it was designed from the beginning to allow you to record video to tape in a digital format that could then be transferred to a computer for editing without having to decompress the video and then recompress it during the transfer process.

DV can and is often used for broadcast purposes. And you can usually tell when you see something that was shot on DV. DV is usually used for low budget stuff, or for situations where a small compact video camera is needed to get something.

DV does not store the same amount of color detail as some of the higher-end digital video formats used for serious professional video. Furthermore, there isn't much in the way of high-end professional equipment that is based on DV. DV tape suffers more from drop-outs and glitches than would be acceptable for serious broadcast TV work. The fact of the matter is, most high-budget prime-time network TV shows are usually shot on 35 mm film!