[FFmpeg-devel] [PATCH 1/2] doc/examples/demuxing: show how to use the reference counting system.

[Clément Bœsch]

From: Clément Bœsch <clement at stupeflix.com>

---
 doc/examples/demuxing.c | 44 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 38 insertions(+), 6 deletions(-)

diff --git a/doc/examples/demuxing.c b/doc/examples/demuxing.c
index 7ae3654..379b1ea 100644
--- a/doc/examples/demuxing.c
+++ b/doc/examples/demuxing.c
@@ -53,6 +53,11 @@ static AVPacket pkt;
 static int video_frame_count = 0;
 static int audio_frame_count = 0;
 
+/* This flag is used to make decoding using ref counting or not. In practice,
+ * you choose one way or another; ref counting notably allowing you to keep the
+ * data as long as you wish. */
+static int use_ref_counting = 0;
+
 static int decode_packet(int *got_frame, int cached)
 {
     int ret = 0;
@@ -115,6 +120,11 @@ static int decode_packet(int *got_frame, int cached)
         }
     }
 
+    /* If we use the reference counter API, we own the data and need to
+     * de-reference it when we don't use it anymore */
+    if (*got_frame && use_ref_counting)
+        av_frame_unref(frame);
+
     return decoded;
 }
 
@@ -125,6 +135,7 @@ static int open_codec_context(int *stream_idx,
     AVStream *st;
     AVCodecContext *dec_ctx = NULL;
     AVCodec *dec = NULL;
+    AVDictionary *opts = NULL;
 
     ret = av_find_best_stream(fmt_ctx, type, -1, -1, NULL, 0);
     if (ret < 0) {
@@ -144,7 +155,10 @@ static int open_codec_context(int *stream_idx,
             return ret;
         }
 
-        if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0) {
+        /* Init the decoders, with or without reference counting */
+        if (use_ref_counting)
+            av_dict_set(&opts, "refcounted_frames", "1", 0);
+        if ((ret = avcodec_open2(dec_ctx, dec, &opts)) < 0) {
             fprintf(stderr, "Failed to open %s codec\n",
                     av_get_media_type_string(type));
             return ret;
@@ -187,18 +201,27 @@ int main (int argc, char **argv)
 {
     int ret = 0, got_frame;
 
-    if (argc != 4) {
-        fprintf(stderr, "usage: %s input_file video_output_file audio_output_file\n"
+    if (argc != 4 && argc != 5) {
+        fprintf(stderr, "usage: %s [-refcount] input_file video_output_file audio_output_file\n"
                 "API example program to show how to read frames from an input file.\n"
                 "This program reads frames from a file, decodes them, and writes decoded\n"
                 "video frames to a rawvideo file named video_output_file, and decoded\n"
-                "audio frames to a rawaudio file named audio_output_file.\n"
+                "audio frames to a rawaudio file named audio_output_file.\n\n"
+                "If the -refcount option is specified, the program use the\n"
+                "reference counting frame system which allows keeping a copy of\n"
+                "the data for longer than one decode call. If unset, it's using\n"
+                "the classic old method.\n"
                 "\n", argv[0]);
         exit(1);
     }
+    if (argc == 5) {
+        use_ref_counting = strcmp(argv[1], "refcount");
+        argv++;
+    }
     src_filename = argv[1];
     video_dst_filename = argv[2];
     audio_dst_filename = argv[3];
+    printf("Use reference counting API: %s\n", use_ref_counting ? "YES" : "NO");
 
     /* register all formats and codecs */
     av_register_all();
@@ -257,7 +280,13 @@ int main (int argc, char **argv)
         goto end;
     }
 
-    frame = avcodec_alloc_frame();
+    /* When using the ref counting system, you need to use the
+     * libavutil/frame.h API, while the classic frame management is available
+     * in libavcodec */
+    if (use_ref_counting)
+        frame = av_frame_alloc();
+    else
+        frame = avcodec_alloc_frame();
     if (!frame) {
         fprintf(stderr, "Could not allocate frame\n");
         ret = AVERROR(ENOMEM);
@@ -336,7 +365,10 @@ end:
         fclose(video_dst_file);
     if (audio_dst_file)
         fclose(audio_dst_file);
-    av_free(frame);
+    if (use_ref_counting)
+        av_frame_free(&frame);
+    else
+        avcodec_free_frame(&frame);
     av_free(video_dst_data[0]);
 
     return ret < 0;
-- 
1.8.4.1