avilib: Reading and writing avi files

 

Copyright (C) 1999 Rainer Johanni <>

avilib is a open source library for dealing with AVI files under Linux or other UNIX operating systems.

It provides a framework for extracting or adding raw audio and single raw (=compressed) frames from/to AVI Files.

It does not deal with any compression issues which have to be handled on a higher level by the user of avilib.

AVI files may have several video and audiotracks.

avilib writes only one video track and (optionally) one audio track and also extracts only the first video and audio track (but input files may contain more than one track, the others just being ingored).

The interface to avilib is kept similar to the quicktime4linux interface (by Adam Williams) with the following important differences:

• since only the first track of video and audio is considered, there is no track argument in any of the routines.
• audio is generally considered as a byte stream and therefore all size arguments used in reading/writing audio are in bytes and not in samples.
• as mentioned above, there are no routines dealing with compression issues.

  Compiling

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Since the library consists only of one c source file, I have not provided a Makefile or similar, just compile with

cc -c avilib.c

Portability

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AVI-Files use little endian numbers throughout the file, I have tried to read/write these numbers in a way which doesn't depent on endianness. This library should therefore also be useable on big endian machines. This feature is not so heavily tested, however.

Usage

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Include "avilib.h" in your source and declare a pointer:

avi_t *avifile;

Open the AVI file with:

avifile = AVI_open_input_file("xxx.avi",1);

or

avifile = AVI_open_output_file("xxx.avi");

You may either only read from the input file (leaving it unchanged) or create a completly new AVI file. There is no editing or append mode available.

Both routines will either return a pointer to avi_t or a zero pointer in the case of an error.

For closing the file, use:

int AVI_close(avi_t *AVI);

Files you have written MUST be closed (the header is written at close time), else they will not be readable by any other software.

Files opened for reading should be closed to free the file descriptor and some data (unless your program is finishing anyway).

Most routines (besides open/close) will return 0 or a usefull number if successfull and a -1 in the case of an error. If an error occured, the external variable AVI_errno is set. See avilib.h for the meaning of the error codes in AVI_errno.

There is also a routine (which acts like perror) to output a description of the last error to stderr:

AVI_print_error(char *str)

After opening the file, you can obtain the parameters of the AVI with the following routines:

long AVI_video_frames(avi_t *AVI);

number of video frames in the file

int AVI_video_width(avi_t AVI);
int AVI_video_height(avi_t AVI);

width and height of the video in pixels

double AVI_frame_rate(avi_t *AVI);

frame rate in frames per second, notice that this is a double value!

char* AVI_video_compressor(avi_t *AVI);

string describing the compressor

int AVI_audio_channels(avi_t *AVI);

number of audio channels, 1 for mono, 2 for stereo, 0 if no audio present

int AVI_audio_bits(avi_t *AVI);

audio bits, usually 8 or 16

int AVI_audio_format(avi_t *AVI);

audio format, most common is 1 for raw PCM, look into avilib.h for others

long AVI_audio_rate(avi_t *AVI);

audio rate in samples/second

long AVI_audio_bytes(avi_t *AVI);

total number of audio bytes in the file

In order to read the video frame by frame, use (frame numbers are starting from 0 !!!!!)

long AVI_frame_size(avi_t *AVI, long frame);

to get the size of frame with number "frame"

long AVI_read_frame(avi_t AVI, char vidbuf);

to read the next frame (frame posittion is advanced by 1 after the read)

int AVI_seek_start(avi_t AVI);
int AVI_set_video_position(avi_t AVI, long frame);

to position in the AVI file
(for reading the frames out of order)

Read audio with

int AVI_set_audio_position(avi_t *AVI, long byte);

to position to an arbitrary byte position within the audio stream

long AVI_read_audio(avi_t AVI, char audbuf, long bytes);

to actually read "bytes" number of audio bytes. the audio position is advanced by "bytes", so there is no need to reposition before every call when reading in order.

When opening the AVI file, avilib looks if the file has an index attached and if this is not the case, it creates one by reading through the whole file.

If you want to read through the file only once, creation of an index is not necessary in that case. You may use AVI_open_input_file with the second argument set to 0 and then use AVI_read_data for readin through the file.

Look to the source for the arguments of AVI_read_data.

After you have opened the file, use the following routines to set the properties of the AVI file:

void AVI_set_video(avi_t AVI, int width, int height, double fps, char compressor); void AVI_set_audio(avi_t *AVI, int channels, long rate, int bits, int format);

with

width, height width and height of the video in pixels

fps frame rate in frames per second, notice that this is a double value!

compressor string describing the compressor

channels number of audio channels, 1 for mono, 2 for stereo, 0 if no audio present

rate audio rate in samples/second

bits audio bits, usually 8 or 16, 0 if no audio present

format audio format, most common is 1 for raw PCM, look into avilib.h for others

to write video frames or audio, use:

int AVI_write_frame(avi_t AVI, char data, long bytes); int AVI_write_audio(avi_t AVI, char data, long bytes);

there is also a feature to duplicate the index entry of the last frame without writing the data again to the file, this should used with care since I don't know if all AVI players can handle the resulting file (xanim can do it!):

int AVI_dup_frame(avi_t *AVI);

AVI files have a 2 GB limit (as has the Linux ext2 file system), avilib will return an error if you try to add more data to the file (and it cares that the file still can be correctly closed). If you want to check yourself how far you are away from that limit (for example to synchronize the amount of audio and video data) use:

long AVI_bytes_remain(avi_t *AVI);

 

 

Revision 1264: /trunk/LemAPI/avi_input

• avi_input.dev

 

 

Revision 1264: /trunk/LemAPI