avformat/file: add fd option for pipe

Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>

doc/protocols.texi

@@ -687,7 +687,7 @@ The accepted syntax is:
 pipe:[@var{number}]
 @end example
 
-@var{number} is the number corresponding to the file descriptor of the
+If @option{fd} isn't specified, @var{number} is the number corresponding to the file descriptor of the
 pipe (e.g. 0 for stdin, 1 for stdout, 2 for stderr).  If @var{number}
 is not specified, by default the stdout file descriptor will be used
 for writing, stdin for reading.
@@ -714,6 +714,8 @@ Set I/O operation maximum block size, in bytes. Default value is
 @code{INT_MAX}, which results in not limiting the requested block size.
 Setting this value reasonably low improves user termination request reaction
 time, which is valuable if data transmission is slow.
+@item fd
+Set file descriptor.
 @end table
 
 Note that some formats (typically MOV), require the output protocol to

libavformat/file.c

@@ -92,6 +92,7 @@ static const AVOption file_options[] = {
 
 static const AVOption pipe_options[] = {
     { "blocksize", "set I/O operation maximum block size", offsetof(FileContext, blocksize), AV_OPT_TYPE_INT, { .i64 = INT_MAX }, 1, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM },
+    { "fd", "set file descriptor", offsetof(FileContext, fd), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM },
     { NULL }
 };
 
@@ -381,6 +382,8 @@ static int pipe_open(URLContext *h, const char *filename, int flags)
     FileContext *c = h->priv_data;
     int fd;
     char *final;
+
+    if (c->fd < 0) {
     av_strstart(filename, "pipe:", &filename);
 
     fd = strtol(filename, &final, 10);
@@ -391,10 +394,12 @@ static int pipe_open(URLContext *h, const char *filename, int flags)
             fd = 0;
         }
     }
+    c->fd = fd;
+    }
+
 #if HAVE_SETMODE
-    setmode(fd, O_BINARY);
+    setmode(c->fd, O_BINARY);
 #endif
-    c->fd = fd;
     h->is_streamed = 1;
     return 0;
 }

libavformat/version.h

@@ -32,7 +32,7 @@
 #include "version_major.h"
 
 #define LIBAVFORMAT_VERSION_MINOR  34
-#define LIBAVFORMAT_VERSION_MICRO 102
+#define LIBAVFORMAT_VERSION_MICRO 103
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \