本文详细介绍了AVI文件的操作方法，包括使用C语言结构体管理AVI文件和流的状态、打开和创建AVI文件、读写视频帧等关键功能。此外，还提供了错误代码说明以及相关API函数的调用示例。
Header Files
#include <dvmavi.h>
Type Definitions
AviFile
This structure maintains the internal state corresponding to an open avi file.
typedef struct AviFile {
PAVIFILE aviHandle;
short numStreams;
int length;
int flags;
} AviFile;
aviHandle
- handle returned by AVIFileOpen
numStreams- The Number of media streams
length- Number of frames in the AVI file
flags- VFW specified flags
AviStream
This structure maintains the internal state corresponding to a single open stream in an avi file. The data in this structure is common to both audio and video streams.
typedef struct AviStream {
PAVISTREAM streamHandle;
int type;
int codec;
int length;
int start;
int sofar;
void *data;
} AviStream;
streamHandle
- Handle returned by AVIGetStream
type- Either AVISTREAM_AUDIO or AVISTREAM_VIDEO
codec- The fcc (not used for audio)
length- Number of frames in the stream for video. Number of blocks for audio.
start- sample number of the first frame
sofar- sample number of the next frame to decompress
data- format specified data (AviVIdeoStream or AviAudioStream
AviVideoStream
This structure maintans information relevant to open video streams.
typedef struct AviVideoStream {
PGETFRAME gf; /* getframe handle for decompression */
PAVISTREAM cs; /* handle to compressed stream (for writes) */
unsigned char *fb; /* framebuffer (for writes) */
short width; /* width of each frame */
short height; /* height of each frame */
short fps; /* frames per second .. */
short keyinterval; /* Interval between key frames */
} AviVideoStream;
gf
- getframe handle for decompression
cs- handle for compressed stream (for writes)
fb- framebuffer (for writes)
width- width of each frame
height- height of each frame
fps- number of frames per second
keyInterval- interval between key frames
Return Code
These represent the possible return values from Dali avi functions. DVM_AVI_OK is returned if all goes well. The error codes are included below. Apart from these, standard video for windows errors may also be returned. These typically bave a AVIERR_ prefix, and are defined in the windows header files.
#define DVM_AVI_BAD_SIZE 1 /* ByteImage size does not match stream size */
#define DVM_AVI_NOT_VIDEO 2 /* Not a video stream */
#define DVM_AVI_GET_FRAME_FAILED 3 /* Call to AVIStreamGetFrame() failed */
#define DVM_AVI_UNINITIALIZED 4 /* Stream not initialized */
#define DVM_AVI_WRITE_FAILED 5 /* Call to AVIStreamWrite() failed */
#define DVM_AVI_FILE_OPEN_FAILED 7 /* AVIFileOpen() failed */
#define DVM_AVI_FILE_INFO_FAILED 8 /* AVIFileInfo() failed */
#define DVM_AVI_BAD_STREAM_NUM 10 /* Requested to read non-existent stream */
#define DVM_AVI_GETSTREAM_FAILED 11 /* AVIFileGetStream() failed */
#define DVM_AVI_STREAM_INFO_FAILED 12 /* AVIStreamInfo() failed */
#define DVM_AVI_READ_FORMAT_FAILED 13 /* AVIStreamReadFormat() failed */
#define DVM_AVI_NOT_RGB 14 /* Video stream is not RGB */
#define DVM_AVI_UNSUPPORTED_TYPE 15 /* Stream type is not supported */
#define DVM_AVI_NO_DECOMPRESSOR 16 /* Decompressor not installed */
Operators
File
int AviFileOpen(char *filename, AviFile **aviFilePtr)
Opens an existing avi file filename for reading. Fills in the aviFilePtr with a ponter to a AviFile structure. Returns AVIERR_MEMORY if memory allocation fails. Can also return other Video For Windows errors. Use AviTranslateError() to get a textual description of the error.int AviFileCreate(char *filename, AviFile **aviFilePtr)
Creates an avi file filename for writing. In case the file exists, it is truncated. Fills in the aviFilePtr with a ponter to a AviFile structure. Returns AVIERR_MEMORY if memory allocation fails. Can also return other Video For Windows errors. Use AviTranslateError() to get a textual description of the error.int AviFileClose(AviFile *aviFile)
Closes the file and frees memory associated with handle aviFile
Stream
int AviStreamOpen(AviFile *aviFile, int streamnum, AviStream **strPtr)
Opens the streamnum -th stream in the avi file aviFile, where the first stream is numbered 0. This stream must already exist in the file aviFile. Fills in the strPtr with a ponter to a AviStream structure. Returns AVIERR_MEMORY if memory allocation fails. Returns DVM_AVI_BAD_STREAM_NUM if there is no stream with this ordinal. Returns DVM_AVI_NOT_RGB if the video bit depth is not 24. Can also return other Video For Windows errors. Use AviTranslateError() to get a textual description of the error.a textual description of the error.int AviStreamClose(AviStream *aviStream)
Closes the stream and frees memory associated with handle aviStream
Video Stream
int AviVideoStreamCreate (AviFile *aviFile, int codec, int w, int h int keyinterval, int quality, int bitrate, AviStream **strPtr)
Create a video stream in the file aviFile, using codec. The frame width and height are given by w and h. The keyinterval specifies the number of frames between key frames, and is used by some codecs. quality is a number between 0 and 100, higher numbers indicating better desired quality. Finally, bitrate is the desired bit rate of the stream in bits per second. The codec value is exactly of the form video for windows expects, and can be obtained from the short textual form by calling a VFW macro. Fills in the strPtr with a ponter to a AviStream structure. Returns AVIERR_MEMORY if memory allocation fails. Can also return other Video For Windows errors. Use AviTranslateError() to get a textual description of the error.int AviStreamStartDecode(AviStream *strPtr)
This should be called prior to calling any functions to decode any frames. Returns AVIERR_NOCOMPRESSOR if no suitable compressor could be found to decode this streamint AviStreamStopDecode(AviStream *strPtr)
This should be called after decoding frames in the stream is complete Frees up memory allocated by AviStreamStartDecodeint AviVideoFrameRead(AviStream *strPtr, ByteImage *r, ByteImage *g, ByteImage *b)
Decodes the next video frame in the stream and fills in the ByteImages r, g, b with its contents. Returns DVM_AVI_NOT_VIDEO if strPtr is not a video stream. Returns DVM_AVI_BAD_SIZE if the ByteImage size does not match the width and height in the stream header. Returns DVM_AVI_GET_FRAME_FAILED if video for windows did not manage to decode the frame.int AviVideoFrameWrite(AviStream *strPtr, ByteImage *r, ByteImage *g, ByteImage *b)
Encodes the next frame given in the ByteImages r, g, b and writes them out to the stream. Returns DVM_AVI_NOT_VIDEO if strPtr is not a video stream. Returns DVM_AVI_BAD_SIZE if the ByteImage size does not match the width and height in the stream header. Can also return other Video For Windows errors. Use AviTranslateError() to get a textual description of the error.a textual description of the error.int AviVideoFrameSeek(AviStream *strPtr, int frameno)
Seeks to the frame position given by frameno. Also returns this frame position.int AviVideoFrameTell(AviStream *strPtr)
Returns the current frame position in the stream.int AviVideoFrameSkip(AviStream *strPtr)
Skips the next frame position in the stream.int AviVideoFrameRewind(AviStream *strPtr)
Sets the frame position to the beginning of the stream.AviStreamGetType(AviStream *aviStream)
AviStreamGetCodec(AviStream *aviStream)
AviStreamGetLength(AviStream *aviStream)
AviStreamGetWidth(AviStream *aviStream)
AviStreamGetHeight(AviStream *aviStream)
AviStreamGetFps(AviStream *aviStream)
These functions (macros in the tcl version) get the corresponding fields from the AviStream and AviVideoStream structure.
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