Implement av_find_best_stream.

Originally committed as revision 26104 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/APIchanges

@@ -13,6 +13,9 @@ libavutil:   2009-03-08
 
 API changes, most recent first:
 
+2010-12-XX - r26104 - lavformat 52.91.0 - av_find_best_stream()
+  Add av_find_best_stream to libavformat/avformat.h.
+
 2010-12-27 - r26103 - lavf 52.90.0
   Add AVFMT_NOSTREAMS flag for formats with no streams,
   like e.g. text metadata.

libavformat/avformat.h

@@ -22,7 +22,7 @@
 #define AVFORMAT_AVFORMAT_H
 
 #define LIBAVFORMAT_VERSION_MAJOR 52
-#define LIBAVFORMAT_VERSION_MINOR 90
+#define LIBAVFORMAT_VERSION_MINOR 91
 #define LIBAVFORMAT_VERSION_MICRO  0
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
@@ -1140,6 +1140,37 @@ AVFormatContext *avformat_alloc_context(void);
  */
 int av_find_stream_info(AVFormatContext *ic);
 
+/**
+ * Find the "best" stream in the file.
+ * The best stream is determined according to various heuristics as the most
+ * likely to be what the user expects.
+ * If the decoder parameter is non-NULL, av_find_best_stream will find the
+ * default decoder for the stream's codec; streams for which no decoder can
+ * be found are ignored.
+ *
+ * @param ic                media file handle
+ * @param type              stream type: video, audio, subtitles, etc.
+ * @param wanted_stream_nb  user-requested stream number,
+ *                          or -1 for automatic selection
+ * @param related_stream    try to find a stream related (eg. in the same
+ *                          program) to this one, or -1 if none
+ * @param decoder_ret       if non-NULL, returns the decoder for the
+ *                          selected stream
+ * @param flags             flags; none are currently defined
+ * @return  the non-negative stream number in case of success,
+ *          AVERROR_STREAM_NOT_FOUND if no stream with the requested type
+ *          could be found,
+ *          AVERROR_DECODER_NOT_FOUND if streams were found but no decoder
+ * @note  If av_find_best_stream returns successfully and decoder_ret is not
+ *        NULL, then *decoder_ret is guaranteed to be set to a valid AVCodec.
+ */
+int av_find_best_stream(AVFormatContext *ic,
+                        enum AVMediaType type,
+                        int wanted_stream_nb,
+                        int related_stream,
+                        AVCodec **decoder_ret,
+                        int flags);
+
 /**
  * Read a transport packet from a media file.
  *

libavformat/utils.c

@@ -2458,6 +2458,67 @@ int av_find_stream_info(AVFormatContext *ic)
     return ret;
 }
 
+static AVProgram *find_program_from_stream(AVFormatContext *ic, int s)
+{
+    int i, j;
+
+    for (i = 0; i < ic->nb_programs; i++)
+        for (j = 0; j < ic->programs[i]->nb_stream_indexes; j++)
+            if (ic->programs[i]->stream_index[j] == s)
+                return ic->programs[i];
+    return NULL;
+}
+
+int av_find_best_stream(AVFormatContext *ic,
+                        enum AVMediaType type,
+                        int wanted_stream_nb,
+                        int related_stream,
+                        AVCodec **decoder_ret,
+                        int flags)
+{
+    int i, nb_streams = ic->nb_streams, stream_number = 0;
+    int ret = AVERROR_STREAM_NOT_FOUND, best_count = -1;
+    unsigned *program = NULL;
+    AVCodec *decoder = NULL, *best_decoder = NULL;
+
+    if (related_stream >= 0 && wanted_stream_nb < 0) {
+        AVProgram *p = find_program_from_stream(ic, related_stream);
+        if (p) {
+            program = p->stream_index;
+            nb_streams = p->nb_stream_indexes;
+        }
+    }
+    for (i = 0; i < nb_streams; i++) {
+        AVStream *st = ic->streams[program ? program[i] : i];
+        AVCodecContext *avctx = st->codec;
+        if (avctx->codec_type != type)
+            continue;
+        if (wanted_stream_nb >= 0 && stream_number++ != wanted_stream_nb)
+            continue;
+        if (decoder_ret) {
+            decoder = avcodec_find_decoder(ic->streams[i]->codec->codec_id);
+            if (!decoder) {
+                if (ret < 0)
+                    ret = AVERROR_DECODER_NOT_FOUND;
+                continue;
+            }
+        }
+        if (best_count >= st->codec_info_nb_frames)
+            continue;
+        best_count = st->codec_info_nb_frames;
+        ret = i;
+        best_decoder = decoder;
+        if (program && i == nb_streams - 1 && ret < 0) {
+            program = NULL;
+            nb_streams = ic->nb_streams;
+            i = 0; /* no related stream found, try again with everything */
+        }
+    }
+    if (decoder_ret)
+        *decoder_ret = best_decoder;
+    return ret;
+}
+
 /*******************************************************/
 
 int av_read_play(AVFormatContext *s)