rtpenc: Allow packetizing H263 according to the old RFC 2190

According to newer RFCs, this packetization scheme should only
be used for interfacing with legacy systems.

Implementing this packetization mode properly requires parsing
the full H263 bitstream to find macroblock boundaries (and knowing
their macroblock and gob numbers and motion vector predictors).

This implementation tries to look for GOB headers (which
can be inserted by using -ps <small number>), but if the GOBs
aren't small enough to fit into the MTU, the packetizer blindly
splits packets at any offset and claims it to be a GOB boundary
(by using Mode A from the RFC). While not correct, this seems
to work with some receivers.

Signed-off-by: Martin Storsjö <martin@martin.st>

1 files changed, 104 insertions, 0 deletions

diff --git a/libavformat/rtpenc_h263_rfc2190.c b/libavformat/rtpenc_h263_rfc2190.c
new file mode 100644
index 0000000000..305c1a27c8
--- /dev/null
+++ b/libavformat/rtpenc_h263_rfc2190.c
@@ -0,0 +1,104 @@
+/*
+ * RTP packetization for H.263 video
+ * Copyright (c) 2012 Martin Storsjo
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "avformat.h"
+#include "rtpenc.h"
+#include "libavcodec/put_bits.h"
+#include "libavcodec/get_bits.h"
+
+struct H263Info {
+    int src;
+    int i;
+    int u;
+    int s;
+    int a;
+    int pb;
+    int tr;
+};
+
+static void send_mode_a(AVFormatContext *s1, const struct H263Info *info,
+                        const uint8_t *buf, int len, int m)
+{
+    RTPMuxContext *s = s1->priv_data;
+    PutBitContext pb;
+
+    init_put_bits(&pb, s->buf, 32);
+    put_bits(&pb, 1, 0); /* F - 0, mode A */
+    put_bits(&pb, 1, 0); /* P - 0, normal I/P */
+    put_bits(&pb, 3, 0); /* SBIT - 0 bits */
+    put_bits(&pb, 3, 0); /* EBIT - 0 bits */
+    put_bits(&pb, 3, info->src); /* SRC - source format */
+    put_bits(&pb, 1, info->i); /* I - inter/intra */
+    put_bits(&pb, 1, info->u); /* U - unrestricted motion vector */
+    put_bits(&pb, 1, info->s); /* S - syntax-baesd arithmetic coding */
+    put_bits(&pb, 1, info->a); /* A - advanced prediction */
+    put_bits(&pb, 4, 0); /* R - reserved */
+    put_bits(&pb, 2, 0); /* DBQ - 0 */
+    put_bits(&pb, 3, 0); /* TRB - 0 */
+    put_bits(&pb, 8, info->tr); /* TR */
+    flush_put_bits(&pb);
+    memcpy(s->buf + 4, buf, len);
+
+    ff_rtp_send_data(s1, s->buf, len + 4, m);
+}
+
+void ff_rtp_send_h263_rfc2190(AVFormatContext *s1, const uint8_t *buf, int size)
+{
+    RTPMuxContext *s = s1->priv_data;
+    int len;
+    GetBitContext gb;
+    struct H263Info info = { 0 };
+
+    s->timestamp = s->cur_timestamp;
+
+    init_get_bits(&gb, buf, size*8);
+    if (get_bits(&gb, 22) == 0x20) { /* Picture Start Code */
+        info.tr  = get_bits(&gb, 8);
+        skip_bits(&gb, 2); /* PTYPE start, H261 disambiguation */
+        skip_bits(&gb, 3); /* Split screen, document camera, freeze picture release */
+        info.src = get_bits(&gb, 3);
+        info.i   = get_bits(&gb, 1);
+        info.u   = get_bits(&gb, 1);
+        info.s   = get_bits(&gb, 1);
+        info.a   = get_bits(&gb, 1);
+        info.pb  = get_bits(&gb, 1);
+    }
+
+    while (size > 0) {
+        len = FFMIN(s->max_payload_size - 4, size);
+
+        /* Look for a better place to split the frame into packets. */
+        if (len < size) {
+            const uint8_t *end = ff_h263_find_resync_marker_reverse(buf,
+                                                                    buf + len);
+            len = end - buf;
+            if (len == s->max_payload_size - 4)
+                av_log(s1, AV_LOG_WARNING,
+                       "No GOB boundary found within MTU size, splitting at "
+                       "a random boundary\n");
+        }
+
+        send_mode_a(s1, &info, buf, len, len == size);
+
+        buf  += len;
+        size -= len;
+    }
+}