mpegts: Remove one memcpy per packet

This was being performed to ensure that a complete packet was held in
contiguous memory, prior to parsing the packet. However, the source buffer
is typically large enough that the packet was already contiguous, so it is
beneficial to return the packet by reference in most cases.

         Before          After
         Mean   StdDev   Mean   StdDev  Change
memcpy    720.7  32.7     649.8  25.1   +10.9%
Overall  2372.7  46.1    2291.7  21.8    +3.5%
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/mpegts.c

@@ -1743,17 +1743,17 @@ static int mpegts_resync(AVFormatContext *s)
 }
 
 /* return -1 if error or EOF. Return 0 if OK. */
-static int read_packet(AVFormatContext *s, uint8_t *buf, int raw_packet_size)
+static int read_packet(AVFormatContext *s, uint8_t *buf, int raw_packet_size, uint8_t **data)
 {
     AVIOContext *pb = s->pb;
-    int skip, len;
+    int len;
 
     for(;;) {
-        len = avio_read(pb, buf, TS_PACKET_SIZE);
+        len = ffio_read_indirect(pb, buf, TS_PACKET_SIZE, data);
         if (len != TS_PACKET_SIZE)
             return len < 0 ? len : AVERROR_EOF;
         /* check packet sync byte */
-        if (buf[0] != 0x47) {
+        if ((*data)[0] != 0x47) {
             /* find a new packet start */
             avio_seek(pb, -TS_PACKET_SIZE, SEEK_CUR);
             if (mpegts_resync(s) < 0)
@@ -1761,19 +1761,25 @@ static int read_packet(AVFormatContext *s, uint8_t *buf, int raw_packet_size)
             else
                 continue;
         } else {
-            skip = raw_packet_size - TS_PACKET_SIZE;
-            if (skip > 0)
-                avio_skip(pb, skip);
             break;
         }
     }
     return 0;
 }
 
+static void finished_reading_packet(AVFormatContext *s, int raw_packet_size)
+{
+    AVIOContext *pb = s->pb;
+    int skip = raw_packet_size - TS_PACKET_SIZE;
+    if (skip > 0)
+        avio_skip(pb, skip);
+}
+
 static int handle_packets(MpegTSContext *ts, int nb_packets)
 {
     AVFormatContext *s = ts->stream;
     uint8_t packet[TS_PACKET_SIZE+FF_INPUT_BUFFER_PADDING_SIZE];
+    uint8_t *data;
     int packet_num, ret = 0;
 
     if (avio_tell(s->pb) != ts->last_pos) {
@@ -1802,10 +1808,11 @@ static int handle_packets(MpegTSContext *ts, int nb_packets)
         packet_num++;
         if (nb_packets != 0 && packet_num >= nb_packets)
             break;
-        ret = read_packet(s, packet, ts->raw_packet_size);
+        ret = read_packet(s, packet, ts->raw_packet_size, &data);
         if (ret != 0)
             break;
-        ret = handle_packet(ts, packet);
+        ret = handle_packet(ts, data);
+        finished_reading_packet(s, ts->raw_packet_size);
         if (ret != 0)
             break;
     }
@@ -1909,6 +1916,7 @@ static int mpegts_read_header(AVFormatContext *s)
         int64_t pcrs[2], pcr_h;
         int packet_count[2];
         uint8_t packet[TS_PACKET_SIZE];
+        uint8_t *data;
 
         /* only read packets */
 
@@ -1924,18 +1932,21 @@ static int mpegts_read_header(AVFormatContext *s)
         nb_pcrs = 0;
         nb_packets = 0;
         for(;;) {
-            ret = read_packet(s, packet, ts->raw_packet_size);
+            ret = read_packet(s, packet, ts->raw_packet_size, &data);
             if (ret < 0)
                 return -1;
-            pid = AV_RB16(packet + 1) & 0x1fff;
+            pid = AV_RB16(data + 1) & 0x1fff;
             if ((pcr_pid == -1 || pcr_pid == pid) &&
-                parse_pcr(&pcr_h, &pcr_l, packet) == 0) {
+                parse_pcr(&pcr_h, &pcr_l, data) == 0) {
+                finished_reading_packet(s, ts->raw_packet_size);
                 pcr_pid = pid;
                 packet_count[nb_pcrs] = nb_packets;
                 pcrs[nb_pcrs] = pcr_h * 300 + pcr_l;
                 nb_pcrs++;
                 if (nb_pcrs >= 2)
                     break;
+            } else {
+                finished_reading_packet(s, ts->raw_packet_size);
             }
             nb_packets++;
         }
@@ -1967,15 +1978,19 @@ static int mpegts_raw_read_packet(AVFormatContext *s,
     int64_t pcr_h, next_pcr_h, pos;
     int pcr_l, next_pcr_l;
     uint8_t pcr_buf[12];
+    uint8_t *data;
 
     if (av_new_packet(pkt, TS_PACKET_SIZE) < 0)
         return AVERROR(ENOMEM);
     pkt->pos= avio_tell(s->pb);
-    ret = read_packet(s, pkt->data, ts->raw_packet_size);
+    ret = read_packet(s, pkt->data, ts->raw_packet_size, &data);
     if (ret < 0) {
         av_free_packet(pkt);
         return ret;
     }
+    if (data != pkt->data)
+        memcpy(pkt->data, data, ts->raw_packet_size);
+    finished_reading_packet(s, ts->raw_packet_size);
     if (ts->mpeg2ts_compute_pcr) {
         /* compute exact PCR for each packet */
         if (parse_pcr(&pcr_h, &pcr_l, pkt->data) == 0) {