DV Files (DV25)

Discussion in 'Computers' started by MarkHastings, Jan 6, 2005.

  1. MarkHastings

    MarkHastings Executive Producer

    Joined:
    Jan 27, 2003
    Messages:
    12,013
    Likes Received:
    1
    Can someone explain the differences between Microsoft AVI/DV Files, .dv files (i.e. DV streams), and DV25 files?

    Anytime I compress a DV file, it's usually an AVI file with Microsofts DV compression. I see that Media Cleaner will export DV files as QuickTime DV Streams (with the .dv extension)...

    But what is DV25?
     
  2. Ken Chan

    Ken Chan Producer

    Joined:
    Apr 11, 1999
    Messages:
    3,302
    Likes Received:
    0
    Basically, DV has both raw video and audio data. AVI and QuickTime are different container formats, which can have combinations of video and audio (and mixed video/audio) streams. So if you had the same DV stored in an AVI and QuickTime, large chunks would be identical between the two files (the actual DV data), while the bits at the beginning and sprinkled around (headers, descriptors, and markers) would be different.

    For AVI, there's also the difference between Type 1 and Type 2. QuickTime stores DV audio and video separately, so it is equivalent to Type 2.

    There's also this DV FAQ.

    I'm not sure what you mean by DV25. Consumer DV is DV25, as compared with DV50 and others. (It more properly refers to the bitrate and particular format of the video compression, since the audio is uncompressed, although only at one of a few sampling rates and bit depths.) There is the aforementioned raw DV25 data, but generally this is not in a file by itself, it's in some container like AVI. Do you have a program that offers to store in a "DV25" format in addition to AVI and QuickTime?
     
  3. MarkHastings

    MarkHastings Executive Producer

    Joined:
    Jan 27, 2003
    Messages:
    12,013
    Likes Received:
    1
    A co-worker says she can export DV files as AVI files (on the PC) with this DV25 codec, but she didn't know how to do the same on the Mac.

    I assumed DV was DV and didn't realize there was another DV compression other than the Microsoft DV codec that comes standard with most PC's.

    Again, I do know Cleaner will export .dv files (which are DV streams) - so I assume (according to what you said about QT and AVI just being "containers" for the DV file) that this .dv is the raw DV stream, but I still wasn't sure if that meant it was DV25 or not.

    [​IMG] [​IMG]
     
  4. Ken Chan

    Ken Chan Producer

    Joined:
    Apr 11, 1999
    Messages:
    3,302
    Likes Received:
    0
    Lossy codecs like MPEG and DV define a set of capabilities, and how bits of data represent those capabilities which can be interpreted by decoders to recreate the picture. Given a data stream, all decoders should generate the same picture; that's sort of the goal of any codec. But codecs vary in how they implement the encoding, balancing factors like speed, bitrate, and quality; they may use some capabilities defined by the codec and not others; and some encoders have bugs. (Decoders can have bugs too, but they are probably more obvious. They can also vary in speed, although obviously they need to be at least real-time; but bitrate is not an issue, and the resulting picture should be the same.)

    Pinnacle's DV25 codec is slightly different than the one from Canopus, or Microsoft, or QuickTime (otherwise there's no point in making your own). Some may be generally considered better or worse. But they are all (supposed to be) compatible, all DV, or more specifically, all DV25.

    With casual viewing, you shouldn't be able to tell which particular DV codec implementation was used, unless you're specifically testing scenes that exploit weaknesses with a given encoder (or the encoder sucks in general).

    The Pinnacle codec that you linked looks like any other software DV (DV25) codec using the standard "dvsd" FOURCC. (Since AVI is a container format, there's a four-character code that identifies the codec used for a particular stream, so that it can be read. Some DV codecs use their own FOURCC.) It's written as a Video for Windows component, using Pentium/SSE instructions. A Mac version would use the same internal logic, but be a completely different animal, written as a QuickTime component using PowerPC/AltiVec instructions. There just isn't one, just like there isn't a Mac version of Doom 3 (although there could be someday).

    If there is no Mac version of the Pinnacle codec, you cannot create such files on the Mac (without resorting to Virtual PC, which should actually work, but would be slow and probably difficult to integrate into your workflow).

    You can take a QuickTime DV, encoded by the Mac's built-in DV25 codec, and reencode that on a PC using Pinnacle's DV25 codec, whether that ends up in an AVI or a "raw stream" file, but I'm not sure why you'd want to do that. Reencoding DV will cause some generational loss. To go from Mac to PC without generational loss, you'd need to use uncompressed video, or a cross-platform lossless codec like this one.

    Why does the client want Pinnacle's? Simply because they heard it was better? That preference would make sense if you were compressing from pristine source, but reencoding DV could very easily destroy any advantage.
     
  5. MarkHastings

    MarkHastings Executive Producer

    Joined:
    Jan 27, 2003
    Messages:
    12,013
    Likes Received:
    1
    Thanks for the explanation Ken. It's making a bit more sense now. I will definitely refer to your post if this comes up again.

    I will also send our engineering dept. that link to the lossless codec. It sounds interesting and would probably be a life saver since we do have to share large files between computers.
     
  6. Ken Chan

    Ken Chan Producer

    Joined:
    Apr 11, 1999
    Messages:
    3,302
    Likes Received:
    0
    There's also this other lossless cross-platform codec. It's supposed to be a lot faster. I have not used either with any serious work. Let me know if you use them or find another.
     

Share This Page