mirror of https://github.com/tongzx/nt5src
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
216 lines
8.7 KiB
216 lines
8.7 KiB
DOC file for AVI Installable compressors
|
|
ToddLa
|
|
----------------------------------------------------------------------------
|
|
|
|
This document covers what happens (from the drivers point of
|
|
view) when AVI loads, saves, edits, and plays a AVI file.
|
|
|
|
|
|
FORMAT OF A AVI FILE -------------------------------------------------------
|
|
|
|
AVI files are RIFF files with the following structure:
|
|
|
|
RIFF('AVI'
|
|
LIST('hdrl'
|
|
avih(<MainAVIHeader>)
|
|
LIST ('strl'
|
|
strh(<Stream header>)
|
|
strf(<Stream format>)
|
|
strd(<Stream data>)
|
|
)
|
|
)
|
|
LIST('movi'
|
|
00??(<driver Data>)
|
|
.
|
|
.
|
|
.
|
|
00??(<driver Data>)
|
|
)
|
|
indx(<AVIIndex>)
|
|
)
|
|
|
|
OPENING a file for decompression -------------------------------------------
|
|
|
|
this is what the driver see's when a AVI file is opened for playback
|
|
or editing.
|
|
|
|
|
|
1. The AVI runtime driver gets the FOURCC driver name from the stream
|
|
header and tries to open the named driver. drivers are
|
|
listed in SYSTEM.INI
|
|
|
|
[Installable Compressors]
|
|
VIDC.SAMP = icsample.drv
|
|
|
|
This example lists a video driver ('VIDC') with the name 'SAMP'.
|
|
|
|
The first message a device driver receives is DRV_OPEN. Your
|
|
device driver should allocate any instance data it uses when
|
|
it processes this message. (Your driver will receive DRV_OPEN
|
|
each time it is opened.)
|
|
|
|
2. If a 'strd' chunk exists for this stream, the AVI runtime driver
|
|
will send your driver an ICM_SETSTATE message. The <MI>lParam1<D>
|
|
parameter will contain a pointer to the data from
|
|
the file.
|
|
|
|
3. Depending on how the AVI runtime driver will use the decompressed
|
|
data, it will send either ICM_DECOMPRESS_GET_FORMAT
|
|
or ICM_DECOMPRESS_QUERY to determine the decompression format.
|
|
|
|
ICM_DECOMPRESS_GET_FORMAT:
|
|
|
|
When your driver gets ICM_DECOMPRESS_GET_FORMAT,
|
|
<MI>lParam1<D> points to the 'strf' data, and <MI>lParam2<D>
|
|
points to a <B>BITMAPINFOHEADER<D> structure.
|
|
|
|
Your driver should fill in the <B>BITMAPINFOHEADER<D> with
|
|
information about the format it will use for decompressing
|
|
the data.
|
|
|
|
If your device driver cannot handle the input format, or
|
|
the input format 'strf' is incorrect, your driver
|
|
should return ICMERR_BADFORMAT to fail the message.
|
|
|
|
ICM_DECOMPRESS_QUERY:
|
|
|
|
When your driver gets ICM_DECOMPRESS_QUERY,
|
|
<MI>lParam1<D> points to the 'strf' data, and <MI>lParam2<D>
|
|
points to a <B>BITMAPINFOHEADER<D> structure. For this message,
|
|
the AVI runtime driver filled the structure with a
|
|
description of the output format it wants to use.
|
|
|
|
The sugested format will be the native or best format
|
|
for the decompressed data. For example,
|
|
if playback is on an 8-bit device, the AVI runtime driver
|
|
will suggest an 8-bit DIB.
|
|
|
|
Your driver does not have to accept the suggested format.
|
|
If you fail the message, the AVI runtime driver will
|
|
suggest alternate formats until your driver accepts one.
|
|
If your driver exhausts the list of formats normally used,
|
|
the AVI runtime driver will request a format with
|
|
ICM_DECOMPRESS_GET_FORMAT.
|
|
|
|
4. When the AVI runtime driver is ready, it sends the
|
|
ICM_DECOMPRESS_BEGIN message to the device driver. The AVI runtime
|
|
driver sets <MI>lParam1<D> to the input format ('strf' data)
|
|
and <MI>lParam2<D> to the decompressed format of the DIB.
|
|
If either of the formats is incorrect, your device driver
|
|
should return ICERR_BADFORMAT.
|
|
|
|
5. The AVI runtime driver sends ICM_DECOMPRESS each time
|
|
it has an image to decompress. The <B>ICDECOMPRESS<D>
|
|
structure specified in <MI>lParam1<D> contains the
|
|
decompression parameters. The AVI runtime driver
|
|
uses the flags in the AVI index to ensure decompression
|
|
will start on key frame boundries,
|
|
|
|
6. Your device driver receives ICM_DECOMPRESS_END when
|
|
the AVI runtime driver no longer needs data decompressed.
|
|
When the device driver is no longer needed the system will
|
|
close it by sending DRV_CLOSE.
|
|
|
|
|
|
COMPRESSING a file ------------------------------------------------------
|
|
|
|
This is the sequence of messages that occur for compressing video data.
|
|
|
|
NOTE: When an AVI file is recompressed, each frame is decompressed to
|
|
a full frame and passed to the decompressor.
|
|
|
|
|
|
1. The first message a device driver receives is DRV_OPEN. Your
|
|
device driver should allocate any instance data it uses when
|
|
it processes this message. (Your driver will receive DRV_OPEN
|
|
each time it is opened.)
|
|
|
|
|
|
2. The AVI runtime driver restores the device driver state
|
|
by sending ICM_SET_STATE. (The state is recalled from the
|
|
strd data chunk of the AVI file. The state information was
|
|
obtained with the ICM_GET_STATE message.)
|
|
|
|
3. The AVI runtime driver determines the size of the buffer needed to
|
|
hold the compressed data format by sending ICM_COMPRESS_GET_FORMAT.
|
|
When requesting the buffer size, the AVI runtime driver uses
|
|
<MI>lParam1<D> to point to a <B>BITMAPINFOHEADER<D> structure
|
|
and sets <MI>lParam2<D> to NULL. Your device driver should
|
|
return the size of the buffer in bytes.
|
|
|
|
4. The AVI runtime driver requests the output format by sending
|
|
ICM_COMPRESS_GET_FORMAT with valid pointers in
|
|
both <MI>lParam1<D> and <MI>lParam2<D>. For this case,
|
|
your device driver should return the output format in
|
|
the buffer pointed to by <MI>lParam2<D>.
|
|
|
|
This data becomes the <B>strf<D> chunk in the AVI file.
|
|
The data must start out like a <B>BITMAPINFOHEADER<D> data
|
|
structure. A color table (if used) follows this information.
|
|
The last part of the data is any additional information
|
|
required to decompress the file.
|
|
|
|
5. When the AVI runtime driver is ready to start compressing data
|
|
it sends the ICM_COMPRESS_BEGIN message.
|
|
The AVI runtime driver uses <MI>lParam1<D> to point to the
|
|
format of the data being compressed, and uses <MI>lParam2<D>
|
|
to point to format for the compressed data. If your device
|
|
driver cannot handle the formats, or if they are incorrect,
|
|
your driver should return ICERR_BADFORMAT to fail the message.
|
|
|
|
6. Before the AVI runtime driver starts compressing data, it sends
|
|
ICM_COMPRESS_GET_SIZE. For this message the AVI runtime driver
|
|
uses <MI>lParam1<D> to point to the input format and uses
|
|
<MI>lParam2<D> to point to the output format.
|
|
|
|
Your driver should return the worst case size (in bytes) that any
|
|
frame can compress to. The AVI runtime driver uses this size
|
|
value when it allocates buffers for the compression.
|
|
|
|
7. The AVI runtime driver sends ICM_COMPRESS for each frame it
|
|
wants compressed. It uses <MI>lParam1<D> to point
|
|
to an <B>ICCOMPRESS<D> structure containing the parameters
|
|
used for compression.
|
|
|
|
Your driver uses the buffers pointed to by the fields of
|
|
<B>ICCOMPRESS<D> for returning information
|
|
about the compressed data.
|
|
|
|
Your driver returns the actual size of the compressed data in the
|
|
<B>biSizeImage<D> field in the <B>BITMAPINFO<D> data structure
|
|
pointed to by the <B>lpbiOutput<D> field of <B>ICCOMPRESS<D>.
|
|
|
|
Your driver returns the chunk ID
|
|
in the buffer specified in the <B>lpckid<D> that it
|
|
assigns to the data.
|
|
|
|
Your driver also returns a DWORD of flags in the buffer pointed
|
|
to by <B>lpdwFlags<D>. The flags will be placed in the AVI
|
|
index for this chunk. The following flags are defined:
|
|
|
|
AVIIF_TWOCC Specifies ckid is a TWOCC.
|
|
|
|
AVIIF_KEYFRAME Specifies this frame is a key frame.
|
|
|
|
Your driver can define its own flags but they must be set in the high
|
|
word only.
|
|
|
|
If your driver handles temporal compression (that is, the compression
|
|
is based on the difference between two frames), it needs to save the
|
|
previous frame(s) for temporal compresssion.
|
|
|
|
8. Your device driver receives ICM_DECOMPRESS_END when
|
|
the AVI runtime driver no longer needs data compressed, or when
|
|
the AVI runtime driver is changing the format or palette.
|
|
If the AVI runtime driver will continue compressing data, it
|
|
will start the sequence by sending ICM_COMPRESS_BEGIN.
|
|
When the device driver is no longer needed the system will
|
|
close it by sending DRV_CLOSE.
|
|
|
|
|
|
The driver might also receive a ICM_COMPRESS_QUERY message
|
|
to determine if it supports the input or output format.
|
|
|
|
COMPRESSING A BUNCH OF FRAMES -------------------------------------------
|
|
|
|
TBD
|