avcodec/cbs: add a helper to read extradata within packet side data

Using ff_cbs_read() on the raw buffer will not parse it as extradata,
resulting in parsing errors for example when handling ISOBMFF avcC.
This helper works around that.

Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/cbs.c

@@ -294,6 +294,19 @@ int ff_cbs_read_packet(CodedBitstreamContext *ctx,
                          pkt->data, pkt->size, 0);
 }
 
+int ff_cbs_read_packet_side_data(CodedBitstreamContext *ctx,
+                                 CodedBitstreamFragment *frag,
+                                 const AVPacket *pkt)
+{
+    size_t side_data_size;
+    const uint8_t *side_data =
+        av_packet_get_side_data(pkt, AV_PKT_DATA_NEW_EXTRADATA,
+                                &side_data_size);
+
+    return cbs_read_data(ctx, frag, NULL,
+                         side_data, side_data_size, 1);
+}
+
 int ff_cbs_read(CodedBitstreamContext *ctx,
                 CodedBitstreamFragment *frag,
                 const uint8_t *data, size_t size)

libavcodec/cbs.h

@@ -276,6 +276,10 @@ int ff_cbs_read_extradata_from_codec(CodedBitstreamContext *ctx,
                                      CodedBitstreamFragment *frag,
                                      const struct AVCodecContext *avctx);
 
+int ff_cbs_read_packet_side_data(CodedBitstreamContext *ctx,
+                                 CodedBitstreamFragment *frag,
+                                 const AVPacket *pkt);
+
 /**
  * Read the data bitstream from a packet into a fragment, then
  * split into units and decompose.