avformat/utils: Improve parsing packets

Up until now, parse_packet() used a stack packet in case the stream is
flushed. But using such a packet is unnecessary as there is an AVPacket
readily available, it just needs to be used. Whether flushing is intended
or not will now be signalled by an explicit parameter rather than by
whether the packet parameter is NULL. This removes a few checks in
parse_packet(), gets rid of the initialization of the stack packet and
also reduces usage of sizeof(AVPacket) in libavformat.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/utils.c

@@ -1441,28 +1441,26 @@ void ff_packet_list_free(AVPacketList **pkt_buf, AVPacketList **pkt_buf_end)
 /**
  * Parse a packet, add all split parts to parse_queue.
  *
- * @param pkt Packet to parse, NULL when flushing the parser at end of stream.
+ * @param pkt   Packet to parse; must not be NULL.
+ * @param flush Indicates whether to flush. If set, pkt must be blank.
  */
-static int parse_packet(AVFormatContext *s, AVPacket *pkt, int stream_index)
+static int parse_packet(AVFormatContext *s, AVPacket *pkt,
+                        int stream_index, int flush)
 {
-    AVPacket out_pkt = { 0 }, flush_pkt = { 0 };
+    AVPacket out_pkt = { 0 };
     AVStream *st = s->streams[stream_index];
-    uint8_t *data = pkt ? pkt->data : NULL;
-    int size      = pkt ? pkt->size : 0;
-    int ret = 0, got_output = 0;
+    uint8_t *data = pkt->data;
+    int size      = pkt->size;
+    int ret = 0, got_output = flush;
 
     av_init_packet(&out_pkt);
 
-    if (!pkt) {
-        av_init_packet(&flush_pkt);
-        pkt        = &flush_pkt;
-        got_output = 1;
-    } else if (!size && st->parser->flags & PARSER_FLAG_COMPLETE_FRAMES) {
+    if (!size && !flush && st->parser->flags & PARSER_FLAG_COMPLETE_FRAMES) {
         // preserve 0-size sync packets
         compute_pkt_fields(s, st, st->parser, pkt, AV_NOPTS_VALUE, AV_NOPTS_VALUE);
     }
 
-    while (size > 0 || (pkt == &flush_pkt && got_output)) {
+    while (size > 0 || (flush && got_output)) {
         int len;
         int64_t next_pts = pkt->pts;
         int64_t next_dts = pkt->dts;
@@ -1546,7 +1544,7 @@ static int parse_packet(AVFormatContext *s, AVPacket *pkt, int stream_index)
     }
 
     /* end of the stream => close and free the parser */
-    if (pkt == &flush_pkt) {
+    if (flush) {
         av_parser_close(st->parser);
         st->parser = NULL;
     }
@@ -1595,7 +1593,7 @@ static int read_frame_internal(AVFormatContext *s, AVPacket *pkt)
             for (i = 0; i < s->nb_streams; i++) {
                 st = s->streams[i];
                 if (st->parser && st->need_parsing)
-                    parse_packet(s, NULL, st->index);
+                    parse_packet(s, pkt, st->index, 1);
             }
             /* all remaining packets are now in parse_queue =>
              * really terminate parsing */
@@ -1683,7 +1681,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
             }
             got_packet = 1;
         } else if (st->discard < AVDISCARD_ALL) {
-            if ((ret = parse_packet(s, pkt, pkt->stream_index)) < 0)
+            if ((ret = parse_packet(s, pkt, pkt->stream_index, 0)) < 0)
                 return ret;
             st->codecpar->sample_rate = st->internal->avctx->sample_rate;
             st->codecpar->bit_rate = st->internal->avctx->bit_rate;