ffmpeg分析系列之二(檔案協議)

static int file_open(URLContext *h, const char *filename, int flags)
{
int access;
int fd;

av_strstart(filename, "file:", &filename);

if (flags & URL_RDWR) {
access = O_CREAT | O_TRUNC | O_RDWR;
} else if (flags & URL_WRONLY) {
access = O_CREAT | O_TRUNC | O_WRONLY;
} else {
access = O_RDONLY;
}
#ifdef O_BINARY
access |= O_BINARY;
#endif
fd = open(filename, access, 0666);
if (fd == -1)
return AVERROR(errno);
h->priv_data = (void *) (intptr_t) fd;
return 0;
}

static int file_read(URLContext *h, unsigned char *buf, int size)
{
int fd = (intptr_t) h->priv_data;
return read(fd, buf, size);
}

static int file_write(URLContext *h, unsigned char *buf, int size)
{
int fd = (intptr_t) h->priv_data;
return write(fd, buf, size);
}

/* XXX: use llseek */
static int64_t file_seek(URLContext *h, int64_t pos, int whence)
{
int fd = (intptr_t) h->priv_data;
if (whence == AVSEEK_SIZE) {
struct stat st;
int ret = fstat(fd, &st);
return ret < 0 ? AVERROR(errno) : st.st_size;
}
return lseek(fd, pos, whence);
}

static int file_close(URLContext *h)
{
int fd = (intptr_t) h->priv_data;
return close(fd);
}

static int file_get_handle(URLContext *h)
{
return (intptr_t) h->priv_data;
}

URLProtocol file_protocol = {
"file",
file_open,
file_read,
file_write,
file_seek,
file_close,
.url_get_file_handle = file_get_handle,
};

#define REGISTER_PROTOCOL(X,x) {
extern URLProtocol x##_protocol;
if(CONFIG_##X##_PROTOCOL) av_register_protocol(&x##_protocol); }

void av_register_all(void)
{
/* 省略部分程式碼 */
/* protocols */
REGISTER_PROTOCOL (FILE, file);
/* 省略部分程式碼 */
}

URLProtocol *first_protocol = NULL;


int av_register_protocol(URLProtocol *protocol)
{
URLProtocol **p;
p = &first_protocol;
while (*p != NULL) p = &(*p)->next;
*p = protocol;
protocol->next = NULL;
return 0;
}