DV Video Data and AVI Files
This article presents issues related to DV video data in relation to AVI files. Both hardware and software vendors need to understand that the format used to store DV data in AVI files can result in an inability by video editing and other relevant applications to read the stored data.
On This Page
 | Background |
| Type-1 Method |
| Type-2 Method |
| DirectShow Filters for DV |
| References |
Background
Microsoft is defining two methods of storing DV video data in AVI files, referred to in this article as type-1 and type-2. You should be aware of two salient points regarding these respective types to keep in mind when designing multimedia devices and their respective software drivers and utilities:
| • | Any DV stored as type-1 cannot be used with VfW-based editors. |
| • | Microsoft is providing DV encoder and decoder filters for DirectShow only, and will not provide support for encoding or decoding DV video data for VfW. |
It is important to understand the format used to store video and audio in an AVI file for VfW.
Although an AVI file can have n number of streams, the most common case is one video ("vids") stream and one audio ("auds") stream. The stream format headers define the format (including compression) of each stream. The existence of one video stream, one audio stream, or both in an AVI file is a de facto standard for VfW.
A native DV stream, on the other hand, interleaves the video and audio data into a single stream. As stated in the introduction, Microsoft is defining two methods (type-1 and type-2) that developers can use for storing DV data in AVI files. The method chosen by a developer will impact the ease with which the data can then be used with current and future video editing applications.
Type-1 Method
The native DV interleaved stream that is produced and consumed in I/O with a DV device contains DV compressed video and pulse code modulated (PCM) audio data. This single interleaved stream can be stored in an AVI file as "ivas" stream (for interleaved video/audio stream). Microsoft refers to this format as a type-1 DV AVI file.
Because the type-1format stores data as a single AVI stream, type-1 DV AVI files are not compatible with VfW. DirectShow, however, easily handles type-1 data streams by routing the streams to a DV Splitter filter that produces a DV-encoded video stream and one or more PCM audio streams for playback or subsequent processing.
Type-2 Method
Interleaved DV data can also be split into a single video stream and one to four audio streams within an AVI file. Microsoft refers to this format of storing DV data as type-2. This format has the advantage of being backward compatible with VfW, because it contains a standard video "vids" stream and at least one standard audio "auds" stream.
Notice that the type-2 file format requires a small amount of additional processing to split and multiplex the DV stream during the functions of capture and transmit to IEEE 1394 DV devices.
DirectShow Filters for DV
DirectShow allows complete access to type-1 and type-2 files for reading and writing (including support for encoding and decoding of DV video):
| • | The DirectShow "DV Splitter" filter can be used to split the interleaved DV stream into video and audio streams that can be written into an AVI file, producing a type-2 DV AVI file. However, keep in mind that the video data is not usable by completely VfW-based applications without a VfW DV codec. Microsoft will not be providing such a codec, as no future development will be allocated to VfW support. |
| • | The DirectShow "DV Mux" filter can be used to multiplex a DV encoded video stream with PCM audio streams to produce a DV interleaved stream. The resulting stream can be written into an AVI file, producing a type-1 DV AVI file, or it can be sent to a combination of a rendering or sink filter and device drivers for transmission to a DV device. |
| • | The DirectShow "DV Encoder" filter can be used to encode video data into the DV compressed video format for storage in DV AVI files or transmission to DV devices. The DirectShow "DV Decoder" filter, conversely, can be used to decode DV compressed video into uncompressed video for display or subsequent processing, such as recompression into a different format. |
Although Microsoft Windows 98 and Windows 2000 ship with a DirectShow VfW-wrapper capture driver to ensure compatibility with WDM, this compatibility is not comprehensive. ISVs should adopt DirectShow as soon as possible for capture and transmit (print to tape) functionality.
References
Download the DV Data in the AVI File Format Specification, Version 1.01.
(File date: June 25, 1997; .rtf file; file size: 215KB)
For information about Microsoft DirectShow architecture, filters, data-types, interfaces, and so on, see the Microsoft DirectX SDK, which includes DirectShow documentation (available through MSDN Professional membership). See http://www.microsoft.com/directx/dxmedia/. DirectX Media documentation is available on-line at http://www.microsoft.com/directx/dxm/.
For more information about DV data formats, see the Specification of Consumer-use Digital VCRs (the "Blue Book"). Detailed information about obtaining the Blue Book (which costs about 50,000 yen) can be obtained by sending your name, company name, address, fax number, and telephone numbers to the following address:
Mr. Mineo Mino,
File Keeper of Dissolved HD Digital VCR Conference and
Manager of Development Planning and Technology Liaison,
Video Equipment Division,
AVC Company,
Matsushita Electric Industrial Co., Ltd.
1-15, Matsuo-Cho, Kadoma-Shi, Osaka, 571-8504, JAPAN
Tel:+81-6-6906-2887
Fax:+81-6-6906-1657
E-mail: mino@ved.mei.co.jp