lavf: deprecate avformat_alloc_output_context() in favor of avformat_alloc_output_context2()

The new function accepts a slightly more intuitive order of paramters,
and returns an error code, thus allowing applications to report a
meaningful error message.

doc/APIchanges

@@ -13,6 +13,10 @@ libavutil:   2011-04-18
 
 API changes, most recent first:
 
+2011-05-22 - xxxxxx - lavf 53.2.0 - avformat.h
+  Introduce avformat_alloc_output_context2() and deprecate
+  avformat_alloc_output_context().
+
 2011-05-22 - xxxxxx - lavfi 2.10.0 - vsrc_buffer.h
   Make libavfilter/vsrc_buffer.h public.
 

ffmpeg.c

@@ -3881,10 +3881,10 @@ static void opt_output_file(const char *filename)
     if (!strcmp(filename, "-"))
         filename = "pipe:";
 
-    oc = avformat_alloc_output_context(last_asked_format, NULL, filename);
+    err = avformat_alloc_output_context2(&oc, NULL, last_asked_format, filename);
     last_asked_format = NULL;
     if (!oc) {
-        print_error(filename, AVERROR(ENOMEM));
+        print_error(filename, err);
         ffmpeg_exit(1);
     }
     file_oformat= oc->oformat;

libavformat/avformat.h

@@ -1054,12 +1054,34 @@ int av_demuxer_open(AVFormatContext *ic, AVFormatParameters *ap);
  */
 AVFormatContext *avformat_alloc_context(void);
 
+#if FF_API_ALLOC_OUTPUT_CONTEXT
 /**
- * Allocate an AVFormatContext.
- * avformat_free_context() can be used to free the context and everything
- * allocated by the framework within it.
+ * @deprecated deprecated in favor of avformat_alloc_output_context2()
  */
-AVFormatContext *avformat_alloc_output_context(const char *format, AVOutputFormat *oformat, const char *filename);
+attribute_deprecated
+AVFormatContext *avformat_alloc_output_context(const char *format,
+                                               AVOutputFormat *oformat,
+                                               const char *filename);
+#endif
+
+/**
+ * Allocate an AVFormatContext for an output format.
+ * avformat_free_context() can be used to free the context and
+ * everything allocated by the framework within it.
+ *
+ * @param *ctx is set to the created format context, or to NULL in
+ * case of failure
+ * @param oformat format to use for allocating the context, if NULL
+ * format_name and filename are used instead
+ * @param format_name the name of output format to use for allocating the
+ * context, if NULL filename is used instead
+ * @param filename the name of the filename to use for allocating the
+ * context, may be NULL
+ * @return >= 0 in case of success, a negative AVERROR code in case of
+ * failure
+ */
+int avformat_alloc_output_context2(AVFormatContext **ctx, AVOutputFormat *oformat,
+                                   const char *format_name, const char *filename);
 
 /**
  * Read packets of a media file to get stream information. This

libavformat/output-example.c

@@ -443,10 +443,10 @@ int main(int argc, char **argv)
     filename = argv[1];
 
     /* allocate the output media context */
-    oc = avformat_alloc_output_context(NULL, NULL, filename);
+    avformat_alloc_output_context2(&oc, NULL, NULL, filename);
     if (!oc) {
         printf("Could not deduce output format from file extension: using MPEG.\n");
-        oc = avformat_alloc_output_context("mpeg", NULL, filename);
+        avformat_alloc_output_context2(&oc, NULL, "mpeg", filename);
     }
     if (!oc) {
         exit(1);

libavformat/utils.c

@@ -2751,8 +2751,13 @@ int av_set_parameters(AVFormatContext *s, AVFormatParameters *ap)
     return 0;
 }
 
-AVFormatContext *avformat_alloc_output_context(const char *format, AVOutputFormat *oformat, const char *filename){
+int avformat_alloc_output_context2(AVFormatContext **avctx, AVOutputFormat *oformat,
+                                   const char *format, const char *filename)
+{
     AVFormatContext *s= avformat_alloc_context();
+    int ret = 0;
+
+    *avctx = NULL;
     if(!s)
         goto nomem;
 
@@ -2761,11 +2766,13 @@ AVFormatContext *avformat_alloc_output_context(const char *format, AVOutputForma
             oformat = av_guess_format(format, NULL, NULL);
             if (!oformat) {
                 av_log(s, AV_LOG_ERROR, "Requested output format '%s' is not a suitable output format\n", format);
+                ret = AVERROR(EINVAL);
                 goto error;
             }
         } else {
             oformat = av_guess_format(NULL, filename, NULL);
             if (!oformat) {
+                ret = AVERROR(EINVAL);
                 av_log(s, AV_LOG_ERROR, "Unable to find a suitable output format for '%s'\n",
                         filename);
                 goto error;
@@ -2787,14 +2794,26 @@ AVFormatContext *avformat_alloc_output_context(const char *format, AVOutputForma
 
     if(filename)
         av_strlcpy(s->filename, filename, sizeof(s->filename));
-    return s;
+    *avctx = s;
+    return 0;
 nomem:
     av_log(s, AV_LOG_ERROR, "Out of memory\n");
+    ret = AVERROR(ENOMEM);
 error:
     avformat_free_context(s);
-    return NULL;
+    return ret;
 }
 
+#if FF_API_ALLOC_OUTPUT_CONTEXT
+AVFormatContext *avformat_alloc_output_context(const char *format,
+                                               AVOutputFormat *oformat, const char *filename)
+{
+    AVFormatContext *avctx;
+    int ret = avformat_alloc_output_context2(&avctx, oformat, format, filename);
+    return ret < 0 ? NULL : avctx;
+}
+#endif
+
 static int validate_codec_tag(AVFormatContext *s, AVStream *st)
 {
     const AVCodecTag *avctag;

libavformat/version.h

@@ -24,7 +24,7 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFORMAT_VERSION_MAJOR 53
-#define LIBAVFORMAT_VERSION_MINOR  1
+#define LIBAVFORMAT_VERSION_MINOR  2
 #define LIBAVFORMAT_VERSION_MICRO  0
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
@@ -68,5 +68,8 @@
 #ifndef FF_API_SDP_CREATE
 #define FF_API_SDP_CREATE              (LIBAVFORMAT_VERSION_MAJOR < 54)
 #endif
+#ifndef FF_API_ALLOC_OUTPUT_CONTEXT
+#define FF_API_ALLOC_OUTPUT_CONTEXT    (LIBAVFORMAT_VERSION_MAJOR < 54)
+#endif
 
 #endif /* AVFORMAT_VERSION_H */