hls: create an AVProgram for each variant

Without the information, application may choose audio from one variant
and video from another variant, which leads to fetch two variants from
network. This enables av_find_best_stream() to find matching audio and
video streams, so that only one variant is fetched from network.
Signed-off-by: LYF <yefei.li@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/hls.c

@@ -504,6 +504,7 @@ static int hls_read_header(AVFormatContext *s)
         struct variant *v = c->variants[i];
         AVInputFormat *in_fmt = NULL;
         char bitrate_str[20];
+        AVProgram * program = NULL;
         if (v->n_segments == 0)
             continue;
 
@@ -549,6 +550,13 @@ static int hls_read_header(AVFormatContext *s)
         if (ret < 0)
             goto fail;
         snprintf(bitrate_str, sizeof(bitrate_str), "%d", v->bandwidth);
+
+        /* Create new AVprogram for variant i */
+        program = av_new_program(s, i);
+        if ( !program )
+            goto fail;
+        av_dict_set(&program->metadata, "variant_bitrate", bitrate_str, 0);
+
         /* Create new AVStreams for each stream in this variant */
         for (j = 0; j < v->ctx->nb_streams; j++) {
             AVStream *st = avformat_new_stream(s, NULL);
@@ -556,6 +564,7 @@ static int hls_read_header(AVFormatContext *s)
                 ret = AVERROR(ENOMEM);
                 goto fail;
             }
+            ff_program_add_stream_index(s, i, stream_offset + j);
             st->id = i;
             avcodec_copy_context(st->codec, v->ctx->streams[j]->codec);
             if (v->bandwidth)