GUACAMOLE-1370: guacenc output to stdout.

src/guacenc/guacenc.c

@@ -30,20 +30,22 @@
 #include <getopt.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include <string.h>
 
 int main(int argc, char* argv[]) {
 
     int i;
 
     /* Load defaults */
     bool force = false;
+    const char* out_file = NULL;
     int width = GUACENC_DEFAULT_WIDTH;
     int height = GUACENC_DEFAULT_HEIGHT;
     int bitrate = GUACENC_DEFAULT_BITRATE;
 
     /* Parse arguments */
     int opt;
-    while ((opt = getopt(argc, argv, "s:r:f")) != -1) {
+    while ((opt = getopt(argc, argv, "s:r:fo:")) != -1) {
 
         /* -s: Dimensions (WIDTHxHEIGHT) */
         if (opt == 's') {
@@ -65,6 +67,10 @@ int main(int argc, char* argv[]) {
         else if (opt == 'f')
             force = true;
 
+        /* -o: Output file ("-" for STDOUT) */
+        else if (opt == 'o')
+            out_file = optarg;
+
         /* Invalid option */
         else {
             goto invalid_options;
@@ -95,6 +101,14 @@ int main(int argc, char* argv[]) {
         return 0;
     }
 
+    /* A single explicit output cannot receive the encodings of multiple
+     * input files */
+    if (out_file != NULL && total_files != 1) {
+        guacenc_log(GUAC_LOG_ERROR, "Only one input file may be given if "
+                "the output is specified with the -o option.");
+        goto invalid_options;
+    }
+
     guacenc_log(GUAC_LOG_INFO, "%i input file(s) provided.", total_files);
 
     guacenc_log(GUAC_LOG_INFO, "Video will be encoded at %ix%i "
@@ -106,15 +120,27 @@ int main(int argc, char* argv[]) {
         /* Get current filename */
         const char* path = argv[i];
 
-        /* Generate output filename */
-        char out_path[4096];
-        int len = snprintf(out_path, sizeof(out_path), "%s.m4v", path);
+        /* Use the explicitly-provided output path, if any, streaming to
+         * STDOUT if "-" was given as the output */
+        const char* out_path;
+        char out_buffer[4096];
+        if (out_file != NULL)
+            out_path = strcmp(out_file, "-") ? out_file : GUACENC_STDOUT_PATH;
+
+        /* Otherwise, generate output filename from input filename */
+        else {
+
+            int len = snprintf(out_buffer, sizeof(out_buffer), "%s.m4v", path);
+
+            /* Do not write if filename exceeds maximum length */
+            if (len >= sizeof(out_buffer)) {
+                guacenc_log(GUAC_LOG_ERROR, "Cannot write output file for "
+                        "\"%s\": Name too long", path);
+                continue;
+            }
+
+            out_path = out_buffer;
 
-        /* Do not write if filename exceeds maximum length */
-        if (len >= sizeof(out_path)) {
-            guacenc_log(GUAC_LOG_ERROR, "Cannot write output file for \"%s\": "
-                    "Name too long", path);
-            continue;
         }
 
         /* Attempt encoding, log granular success/failure at debug level */
@@ -148,6 +174,7 @@ int main(int argc, char* argv[]) {
             " [-s WIDTHxHEIGHT]"
             " [-r BITRATE]"
             " [-f]"
+            " [-o OUTPUT]"
             " [FILE]...\n", argv[0]);
 
     return 1;

src/guacenc/guacenc.h

@@ -47,5 +47,11 @@
  */
 #define GUACENC_DEFAULT_LOG_LEVEL GUAC_LOG_INFO
 
+/**
+ * The libavformat URL of the current process' STDOUT, as used when encoded
+ * video should be streamed to STDOUT rather than written to a file.
+ */
+#define GUACENC_STDOUT_PATH "pipe:1"
+
 #endif
 

src/guacenc/man/guacenc.1.in

@@ -26,6 +26,7 @@ guacenc \- Guacamole video encoder
 [\fB-s\fR \fIWIDTH\fRx\fIHEIGHT\fR]
 [\fB-r\fR \fIBITRATE\fR]
 [\fB-f\fR]
+[\fB-o\fR \fIOUTPUT\fR]
 [\fIFILE\fR]...
 .
 .SH DESCRIPTION
@@ -46,6 +47,13 @@ overridden with the \fB-s\fR and \fB-r\fR options respectively. Existing files
 will not be overwritten; the encoding process for any input file will be
 aborted if it would result in overwriting an existing file.
 .P
+Alternatively, the \fB-o\fR option may be used to specify the output file
+explicitly. In typical UNIX fashion, specifying "-" as the output file will
+cause the encoded video to be streamed to STDOUT rather than written to a
+file, allowing the video to be piped to another process or streamed as a
+download while it is still being encoded. As only a single output may be
+specified, only one \fIFILE\fR may be given if \fB-o\fR is used.
+.P
 Guacamole acquires a write lock on recordings as they are being written. By
 default,
 .B guacenc
@@ -75,6 +83,13 @@ Overrides the default behavior of
 .B guacenc
 such that input files will be encoded even if they appear to be recordings of
 in-progress Guacamole sessions.
+.TP
+\fB-o\fR \fIOUTPUT\fR
+Writes the encoded video to \fIOUTPUT\fR instead of a file named after the
+input file. If \fIOUTPUT\fR is "-", the encoded video will be streamed to
+STDOUT rather than written to a file; as all log messages are written to
+STDERR, they will not interfere with the video stream. Only one \fIFILE\fR may
+be given when this option is used.
 .
 .SH SEE ALSO
 .BR guaclog (1)

src/guacenc/video.c

@@ -29,6 +29,7 @@
 #include <libavformat/avformat.h>
 #endif
 #include <libavutil/common.h>
+#include <libavutil/dict.h>
 #include <libavutil/imgutils.h>
 #include <libswscale/swscale.h>
 #include <guacamole/client.h>
@@ -41,6 +42,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <inttypes.h>
+#include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
@@ -54,8 +56,16 @@ guacenc_video* guacenc_video_alloc(const char* path, const char* codec_name,
     int ret;
     int failed_header = 0;
 
+    /* The container format cannot be guessed from a pipe URL and must be
+     * specified explicitly. The "ipod" container is used, matching the
+     * container that would be guessed from the ".m4v" extension of the output
+     * files normally produced */
+    bool is_pipe = (strncmp(path, "pipe:", 5) == 0);
+    const char* format_name = is_pipe ? "ipod" : NULL;
+
     /* allocate the output media context */
-    avformat_alloc_output_context2(&container_format_context, NULL, NULL, path);
+    avformat_alloc_output_context2(&container_format_context, NULL,
+            format_name, path);
     if (container_format_context == NULL) {
         guacenc_log(GUAC_LOG_ERROR, "Failed to determine container from output file name");
         goto fail_codec;
@@ -130,8 +140,17 @@ guacenc_video* guacenc_video_alloc(const char* path, const char* codec_name,
         }
     }
 
+    /* A pipe cannot be seeked backwards to finalize the container once
+     * encoding is complete, so fragmented MP4 must be used to produce a
+     * usable video stream */
+    AVDictionary* header_options = NULL;
+    if (is_pipe)
+        av_dict_set(&header_options, "movflags",
+                "frag_keyframe+empty_moov", 0);
+
     /* write the stream header, if needed */
-    ret = avformat_write_header(container_format_context, NULL);
+    ret = avformat_write_header(container_format_context, &header_options);
+    av_dict_free(&header_options);
     if (ret < 0) {
         guacenc_log(GUAC_LOG_ERROR, "Error occurred while writing output file header.");
         failed_header = true;
@@ -163,8 +182,9 @@ guacenc_video* guacenc_video_alloc(const char* path, const char* codec_name,
 fail_output_file:
     avio_close(container_format_context->pb);
 
-    /* Delete the file that was created if it was actually created */
-    if (unlink(path) == -1 && errno != ENOENT)
+    /* Delete the file that was created if it was actually created (no file
+     * exists to be deleted if output was written to a pipe) */
+    if (!is_pipe && unlink(path) == -1 && errno != ENOENT)
         guacenc_log(GUAC_LOG_WARNING, "Failed output file \"%s\" could not "
                 "be automatically deleted: %s", path, strerror(errno));