avcodec/dvbsubdec: Allow selecting the substream, or all substreams

Fixes Ticket 2161
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/decoders.texi

@@ -209,6 +209,8 @@ Never compute CLUT
 @item 1
 Always compute CLUT and override the one provided in the stream.
 @end table
+@item dvb_substream
+Selects the dvb substream, or all substreams if -1 which is default.
 
 @end table
 

libavcodec/dvbsubdec.c

@@ -238,6 +238,7 @@ typedef struct DVBSubContext {
     int compute_edt; /**< if 1 end display time calculated using pts
                           if 0 (Default) calculated using time out */
     int compute_clut;
+    int substream;
     int64_t prev_start;
     DVBSubRegion *region_list;
     DVBSubCLUT   *clut_list;
@@ -368,17 +369,22 @@ static av_cold int dvbsub_init_decoder(AVCodecContext *avctx)
     int i, r, g, b, a = 0;
     DVBSubContext *ctx = avctx->priv_data;
 
-    if (!avctx->extradata || (avctx->extradata_size < 4) || ((avctx->extradata_size % 5 != 0) && (avctx->extradata_size != 4))) {
+    if (ctx->substream < 0) {
+        ctx->composition_id = -1;
+        ctx->ancillary_id   = -1;
+    } else if (!avctx->extradata || (avctx->extradata_size < 4) || ((avctx->extradata_size % 5 != 0) && (avctx->extradata_size != 4))) {
         av_log(avctx, AV_LOG_WARNING, "Invalid DVB subtitles stream extradata!\n");
         ctx->composition_id = -1;
         ctx->ancillary_id   = -1;
     } else {
-        if (avctx->extradata_size > 5) {
-            av_log(avctx, AV_LOG_WARNING, "Decoding first DVB subtitles sub-stream\n");
+        if (avctx->extradata_size > 5*ctx->substream + 2) {
+            ctx->composition_id = AV_RB16(avctx->extradata + 5*ctx->substream);
+            ctx->ancillary_id   = AV_RB16(avctx->extradata + 5*ctx->substream + 2);
+        } else {
+            av_log(avctx, AV_LOG_WARNING, "Selected DVB subtitles sub-stream %d is not available\n", ctx->substream);
+            ctx->composition_id = AV_RB16(avctx->extradata);
+            ctx->ancillary_id   = AV_RB16(avctx->extradata + 2);
         }
-
-        ctx->composition_id = AV_RB16(avctx->extradata);
-        ctx->ancillary_id   = AV_RB16(avctx->extradata + 2);
     }
 
     ctx->version = -1;
@@ -1715,6 +1721,7 @@ end:
 static const AVOption options[] = {
     {"compute_edt", "compute end of time using pts or timeout", offsetof(DVBSubContext, compute_edt), FF_OPT_TYPE_INT, {.i64 = 0}, 0, 1, DS},
     {"compute_clut", "compute clut when not available(-1) or always(1) or never(0)", offsetof(DVBSubContext, compute_clut), FF_OPT_TYPE_INT, {.i64 = -1}, -1, 1, DS},
+    {"dvb_substream", "", offsetof(DVBSubContext, substream), FF_OPT_TYPE_INT, {.i64 = -1}, -1, 63, DS},
     {NULL}
 };
 static const AVClass dvbsubdec_class = {