avformat/hls: Fix missing streams in some cases with MPEG TS

HLS demuxer calls the subdemuxer avformat_find_stream_info() while
overriding the subdemuxer AVFMTCTX_NOHEADER flag by clearing it.
However, this prevents some streams in some MPEG TS streams from being
detected properly.

Simply removing the clearing of the flag would cause the inner
avformat_find_stream_info() call to take longer in some cases, without
a way to control it.

To fix the issue, do not clear the flag but propagate it to HLS demuxer.
To avoid the above-mentioned mandatory delay, the call to
avformat_find_stream_info() is dropped except in the HLS ID3 timestamped
case. The HLS demuxer user should be calling avformat_find_stream_info()
on the HLS demuxer if it wants to find the stream info.

The main streams are now created dynamically after read_header time if
the subdemuxer uses AVFMTCTX_NOHEADER (mpegts).

Subdemuxer avformat_find_stream_info() is still called for the HLS ID3
timestamped case as the HLS demuxer needs to know the packet durations
to properly interleave ID3 timestamped streams with MPEG TS streams on
sub-segment level.

Fixes ticket #4930.

libavformat/hls.c

@@ -98,6 +98,7 @@ struct playlist {
     int index;
     AVFormatContext *ctx;
     AVPacket pkt;
+    int has_noheader_flag;
 
     /* main demuxer streams associated with this playlist
      * indexed by the subdemuxer stream indexes */
@@ -1555,6 +1556,27 @@ static int update_streams_from_subdemuxer(AVFormatContext *s, struct playlist *p
     return 0;
 }
 
+static void update_noheader_flag(AVFormatContext *s)
+{
+    HLSContext *c = s->priv_data;
+    int flag_needed = 0;
+    int i;
+
+    for (i = 0; i < c->n_playlists; i++) {
+        struct playlist *pls = c->playlists[i];
+
+        if (pls->has_noheader_flag) {
+            flag_needed = 1;
+            break;
+        }
+    }
+
+    if (flag_needed)
+        s->ctx_flags |= AVFMTCTX_NOHEADER;
+    else
+        s->ctx_flags &= ~AVFMTCTX_NOHEADER;
+}
+
 static int hls_read_header(AVFormatContext *s)
 {
     void *u = (s->flags & AVFMT_FLAG_CUSTOM_IO) ? NULL : s->pb;
@@ -1725,14 +1747,23 @@ static int hls_read_header(AVFormatContext *s)
             pls->id3_deferred_extra = NULL;
         }
 
-        pls->ctx->ctx_flags &= ~AVFMTCTX_NOHEADER;
-        ret = avformat_find_stream_info(pls->ctx, NULL);
-        if (ret < 0)
-            goto fail;
-
         if (pls->is_id3_timestamped == -1)
             av_log(s, AV_LOG_WARNING, "No expected HTTP requests have been made\n");
 
+        /*
+         * For ID3 timestamped raw audio streams we need to detect the packet
+         * durations to calculate timestamps in fill_timing_for_id3_timestamped_stream(),
+         * but for other streams we can rely on our user calling avformat_find_stream_info()
+         * on us if they want to.
+         */
+        if (pls->is_id3_timestamped) {
+            ret = avformat_find_stream_info(pls->ctx, NULL);
+            if (ret < 0)
+                goto fail;
+        }
+
+        pls->has_noheader_flag = !!(pls->ctx->ctx_flags & AVFMTCTX_NOHEADER);
+
         /* Create new AVStreams for each stream in this playlist */
         ret = update_streams_from_subdemuxer(s, pls);
         if (ret < 0)
@@ -1743,6 +1774,8 @@ static int hls_read_header(AVFormatContext *s)
         add_metadata_from_renditions(s, pls, AVMEDIA_TYPE_SUBTITLE);
     }
 
+    update_noheader_flag(s);
+
     return 0;
 fail:
     free_playlist_list(c);
@@ -1914,6 +1947,19 @@ static int hls_read_packet(AVFormatContext *s, AVPacket *pkt)
     if (minplaylist >= 0) {
         struct playlist *pls = c->playlists[minplaylist];
 
+        ret = update_streams_from_subdemuxer(s, pls);
+        if (ret < 0) {
+            av_packet_unref(&pls->pkt);
+            reset_packet(&pls->pkt);
+            return ret;
+        }
+
+        /* check if noheader flag has been cleared by the subdemuxer */
+        if (pls->has_noheader_flag && !(pls->ctx->ctx_flags & AVFMTCTX_NOHEADER)) {
+            pls->has_noheader_flag = 0;
+            update_noheader_flag(s);
+        }
+
         if (pls->pkt.stream_index >= pls->n_main_streams) {
             av_log(s, AV_LOG_ERROR, "stream index inconsistency: index %d, %d main streams, %d subdemuxer streams\n",
                    pls->pkt.stream_index, pls->n_main_streams, pls->ctx->nb_streams);