avcodec/packet: move AVPacketList definition and function helpers over from libavformat

And replace the flags parameter with a function callback that can be used to
copy the contents of the packet (e.g, av_packet_ref and av_packet_copy_props).

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

libavcodec/avpacket.c

@@ -726,6 +726,73 @@ FF_ENABLE_DEPRECATION_WARNINGS
 #endif
 }
 
+int avpriv_packet_list_put(AVPacketList **packet_buffer,
+                           AVPacketList **plast_pktl,
+                           AVPacket      *pkt,
+                           int (*copy)(AVPacket *dst, const AVPacket *src),
+                           int flags)
+{
+    AVPacketList *pktl = av_mallocz(sizeof(AVPacketList));
+    int ret;
+
+    if (!pktl)
+        return AVERROR(ENOMEM);
+
+    if (copy) {
+        ret = copy(&pktl->pkt, pkt);
+        if (ret < 0) {
+            av_free(pktl);
+            return ret;
+        }
+    } else {
+        ret = av_packet_make_refcounted(pkt);
+        if (ret < 0) {
+            av_free(pktl);
+            return ret;
+        }
+        av_packet_move_ref(&pktl->pkt, pkt);
+    }
+
+    if (*packet_buffer)
+        (*plast_pktl)->next = pktl;
+    else
+        *packet_buffer = pktl;
+
+    /* Add the packet in the buffered packet list. */
+    *plast_pktl = pktl;
+    return 0;
+}
+
+int avpriv_packet_list_get(AVPacketList **pkt_buffer,
+                           AVPacketList **pkt_buffer_end,
+                           AVPacket      *pkt)
+{
+    AVPacketList *pktl;
+    if (!*pkt_buffer)
+        return AVERROR(EAGAIN);
+    pktl        = *pkt_buffer;
+    *pkt        = pktl->pkt;
+    *pkt_buffer = pktl->next;
+    if (!pktl->next)
+        *pkt_buffer_end = NULL;
+    av_freep(&pktl);
+    return 0;
+}
+
+void avpriv_packet_list_free(AVPacketList **pkt_buf, AVPacketList **pkt_buf_end)
+{
+    AVPacketList *tmp = *pkt_buf;
+
+    while (tmp) {
+        AVPacketList *pktl = tmp;
+        tmp = pktl->next;
+        av_packet_unref(&pktl->pkt);
+        av_freep(&pktl);
+    }
+    *pkt_buf     = NULL;
+    *pkt_buf_end = NULL;
+}
+
 int ff_side_data_set_encoder_stats(AVPacket *pkt, int quality, int64_t *error, int error_count, int pict_type)
 {
     uint8_t *side_data;