rtp: Initial H.261 support

The packetizer only supports splitting at GOB headers - if
such aren't available frequently enough, it splits at any
random byte offset (not at a macroblock boundary either, which
would be allowed by the spec) and sends a payload header pretend
that it starts with a GOB header.

As long as a receiver doesn't try to handle such cases cleverly
but just drops broken frames, this shouldn't matter too much
in practice.
Signed-off-by: Martin Storsjö <martin@martin.st>

Changelog

@@ -7,6 +7,7 @@ version <next>:
 - avplay now exits by default at the end of playback
 - XCB-based screen-grabber
 - creating DASH compatible fragmented MP4, MPEG-DASH segmenting muxer
+- H.261 RTP payload format (RFC 4587) depacketizer and experimental packetizer
 
 
 version 11:

libavformat/Makefile

@@ -32,6 +32,7 @@ OBJS-$(CONFIG_RTPDEC)                    += rdt.o                       \
                                             rtpdec_amr.o                \
                                             rtpdec_asf.o                \
                                             rtpdec_g726.o               \
+                                            rtpdec_h261.o               \
                                             rtpdec_h263.o               \
                                             rtpdec_h263_rfc2190.o       \
                                             rtpdec_h264.o               \
@@ -290,6 +291,7 @@ OBJS-$(CONFIG_RTP_MUXER)                 += rtp.o         \
                                             rtpenc_aac.o     \
                                             rtpenc_latm.o    \
                                             rtpenc_amr.o     \
+                                            rtpenc_h261.o    \
                                             rtpenc_h263.o    \
                                             rtpenc_h263_rfc2190.o \
                                             rtpenc_hevc.o    \

libavformat/rtpdec.c

@@ -66,6 +66,7 @@ void ff_register_rtp_dynamic_payload_handlers(void)
     ff_register_dynamic_payload_handler(&ff_g726_24_dynamic_handler);
     ff_register_dynamic_payload_handler(&ff_g726_32_dynamic_handler);
     ff_register_dynamic_payload_handler(&ff_g726_40_dynamic_handler);
+    ff_register_dynamic_payload_handler(&ff_h261_dynamic_handler);
     ff_register_dynamic_payload_handler(&ff_h263_1998_dynamic_handler);
     ff_register_dynamic_payload_handler(&ff_h263_2000_dynamic_handler);
     ff_register_dynamic_payload_handler(&ff_h263_rfc2190_dynamic_handler);

libavformat/rtpdec_formats.h

@@ -41,6 +41,7 @@ extern RTPDynamicProtocolHandler ff_g726_16_dynamic_handler;
 extern RTPDynamicProtocolHandler ff_g726_24_dynamic_handler;
 extern RTPDynamicProtocolHandler ff_g726_32_dynamic_handler;
 extern RTPDynamicProtocolHandler ff_g726_40_dynamic_handler;
+extern RTPDynamicProtocolHandler ff_h261_dynamic_handler;
 extern RTPDynamicProtocolHandler ff_h263_1998_dynamic_handler;
 extern RTPDynamicProtocolHandler ff_h263_2000_dynamic_handler;
 extern RTPDynamicProtocolHandler ff_h263_rfc2190_dynamic_handler;

libavformat/rtpdec_h261.c

+/*
+ * RTP parser for H.261 payload format (RFC 4587)
+ * Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.com>
+ *
+ * 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 "libavcodec/get_bits.h"
+#include "avformat.h"
+#include "rtpdec_formats.h"
+
+#define RTP_H261_PAYLOAD_HEADER_SIZE 4
+
+struct PayloadContext {
+    AVIOContext *buf;
+    uint8_t      endbyte;
+    int          endbyte_bits;
+    uint32_t     timestamp;
+};
+
+static av_cold PayloadContext *h261_new_context(void)
+{
+    return av_mallocz(sizeof(PayloadContext));
+}
+
+static void h261_free_dyn_buffer(AVIOContext **dyn_buf)
+{
+    uint8_t *ptr_dyn_buffer;
+    avio_close_dyn_buf(*dyn_buf, &ptr_dyn_buffer);
+    av_free(ptr_dyn_buffer);
+    *dyn_buf = NULL;
+}
+
+static av_cold void h261_free_context(PayloadContext *pl_ctx)
+{
+    /* return if context is invalid */
+    if (!pl_ctx)
+        return;
+
+    /* free buffer if it is valid */
+    if (pl_ctx->buf) {
+        h261_free_dyn_buffer(&pl_ctx->buf);
+    }
+
+    /* free context */
+    av_free(pl_ctx);
+}
+
+static av_cold int h261_init(AVFormatContext *ctx, int st_index,
+                             PayloadContext *data)
+{
+    if (st_index < 0)
+        return 0;
+
+    ctx->streams[st_index]->need_parsing = AVSTREAM_PARSE_FULL;
+
+    return 0;
+}
+
+static int h261_handle_packet(AVFormatContext *ctx, PayloadContext *rtp_h261_ctx,
+                              AVStream *st, AVPacket *pkt, uint32_t *timestamp,
+                              const uint8_t *buf, int len, uint16_t seq,
+                              int flags)
+{
+    int sbit, ebit, gobn, mbap, quant;
+    int res;
+
+    /* drop data of previous packets in case of non-continuous (lossy) packet stream */
+    if (rtp_h261_ctx->buf && rtp_h261_ctx->timestamp != *timestamp) {
+        h261_free_dyn_buffer(&rtp_h261_ctx->buf);
+        rtp_h261_ctx->endbyte_bits = 0;
+    }
+
+    /* sanity check for size of input packet: 1 byte payload at least */
+    if (len < RTP_H261_PAYLOAD_HEADER_SIZE + 1) {
+        av_log(ctx, AV_LOG_ERROR, "Too short RTP/H.261 packet, got %d bytes\n", len);
+        return AVERROR_INVALIDDATA;
+    }
+
+    /*
+     * decode the H.261 payload header according to section 4.1 of RFC 4587:
+     * (uses 4 bytes between RTP header and H.261 stream per packet)
+     *
+     *    0                   1                   2                   3
+     *    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+     *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     *   |SBIT |EBIT |I|V| GOBN  |   MBAP  |  QUANT  |  HMVD   |  VMVD   |
+     *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+     *
+     *      Start bit position (SBIT): 3 bits
+     *      End bit position (EBIT): 3 bits
+     *      INTRA-frame encoded data (I): 1 bit
+     *      Motion Vector flag (V): 1 bit
+     *      GOB number (GOBN): 4 bits
+     *      Macroblock address predictor (MBAP): 5 bits
+     *      Quantizer (QUANT): 5 bits
+     *      Horizontal motion vector data (HMVD): 5 bits
+     *      Vertical motion vector data (VMVD): 5 bits
+     */
+    sbit  =  (buf[0] >> 5) & 0x07;
+    ebit  =  (buf[0] >> 2) & 0x07;
+    gobn  =  (buf[1] >> 4) & 0x0f;
+    mbap  = ((buf[1] << 1) & 0x1e) | ((buf[2] >> 7) & 0x01);
+    quant =  (buf[2] >> 2) & 0x1f;
+
+    /* pass the H.261 payload header and continue with the actual payload */
+    buf += RTP_H261_PAYLOAD_HEADER_SIZE;
+    len -= RTP_H261_PAYLOAD_HEADER_SIZE;
+
+    /* start frame buffering with new dynamic buffer */
+    if (!rtp_h261_ctx->buf) {
+        /* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, quant=0 */
+        if (!gobn && !sbit && !mbap && !quant) {
+            res = avio_open_dyn_buf(&rtp_h261_ctx->buf);
+            if (res < 0)
+                return res;
+            /* update the timestamp in the frame packet with the one from the RTP packet */
+            rtp_h261_ctx->timestamp = *timestamp;
+        } else {
+            /* frame not started yet, need more packets */
+            return AVERROR(EAGAIN);
+        }
+    }
+
+    /* do the "byte merging" at the boundaries of two consecutive frame fragments */
+    if (rtp_h261_ctx->endbyte_bits || sbit) {
+        if (rtp_h261_ctx->endbyte_bits == sbit) {
+            rtp_h261_ctx->endbyte     |= buf[0] & (0xff >> sbit);
+            rtp_h261_ctx->endbyte_bits = 0;
+            buf++;
+            len--;
+            avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
+        } else {
+            /* ebit/sbit values inconsistent, assuming packet loss */
+            GetBitContext gb;
+            init_get_bits(&gb, buf, len*8 - ebit);
+            skip_bits(&gb, sbit);
+            if (rtp_h261_ctx->endbyte_bits) {
+                rtp_h261_ctx->endbyte |= get_bits(&gb, 8 - rtp_h261_ctx->endbyte_bits);
+                avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
+            }
+            while (get_bits_left(&gb) >= 8)
+                avio_w8(rtp_h261_ctx->buf, get_bits(&gb, 8));
+            rtp_h261_ctx->endbyte_bits = get_bits_left(&gb);
+            if (rtp_h261_ctx->endbyte_bits)
+                rtp_h261_ctx->endbyte = get_bits(&gb, rtp_h261_ctx->endbyte_bits) <<
+                                        (8 - rtp_h261_ctx->endbyte_bits);
+            ebit = 0;
+            len  = 0;
+        }
+    }
+    if (ebit) {
+        if (len > 0)
+            avio_write(rtp_h261_ctx->buf, buf, len - 1);
+        rtp_h261_ctx->endbyte_bits = 8 - ebit;
+        rtp_h261_ctx->endbyte      = buf[len - 1] & (0xff << ebit);
+    } else {
+        avio_write(rtp_h261_ctx->buf, buf, len);
+    }
+
+    /* RTP marker bit means: last fragment of current frame was received;
+       otherwise, an additional fragment is needed for the current frame */
+    if (!(flags & RTP_FLAG_MARKER))
+        return AVERROR(EAGAIN);
+
+    /* write the completed last byte from the "byte merging" */
+    if (rtp_h261_ctx->endbyte_bits)
+        avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte);
+    rtp_h261_ctx->endbyte_bits = 0;
+
+    /* close frame buffering and create resulting A/V packet */
+    res = ff_rtp_finalize_packet(pkt, &rtp_h261_ctx->buf, st->index);
+    if (res < 0)
+        return res;
+
+    return 0;
+}
+
+RTPDynamicProtocolHandler ff_h261_dynamic_handler = {
+    .enc_name          = "H261",
+    .codec_type        = AVMEDIA_TYPE_VIDEO,
+    .codec_id          = AV_CODEC_ID_H261,
+    .init              = h261_init,
+    .alloc             = h261_new_context,
+    .free              = h261_free_context,
+    .parse_packet      = h261_handle_packet,
+    .static_payload_id = 31,
+};

libavformat/rtpenc.c

@@ -49,6 +49,7 @@ static const AVClass rtp_muxer_class = {
 static int is_supported(enum AVCodecID id)
 {
     switch(id) {
+    case AV_CODEC_ID_H261:
     case AV_CODEC_ID_H263:
     case AV_CODEC_ID_H263P:
     case AV_CODEC_ID_H264:
@@ -88,7 +89,7 @@ static int is_supported(enum AVCodecID id)
 static int rtp_write_header(AVFormatContext *s1)
 {
     RTPMuxContext *s = s1->priv_data;
-    int n;
+    int n, ret = AVERROR(EINVAL);
     AVStream *st;
 
     if (s1->nb_streams != 1) {
@@ -191,6 +192,17 @@ static int rtp_write_header(AVFormatContext *s1)
         s->max_payload_size = n * TS_PACKET_SIZE;
         s->buf_ptr = s->buf;
         break;
+    case AV_CODEC_ID_H261:
+        if (s1->strict_std_compliance > FF_COMPLIANCE_EXPERIMENTAL) {
+            av_log(s, AV_LOG_ERROR,
+                   "Packetizing H261 is experimental and produces incorrect "
+                   "packetization for cases where GOBs don't fit into packets "
+                   "(even though most receivers may handle it just fine). "
+                   "Please set -f_strict experimental in order to enable it.\n");
+            ret = AVERROR_EXPERIMENTAL;
+            goto fail;
+        }
+        break;
     case AV_CODEC_ID_H264:
         /* check for H.264 MP4 syntax */
         if (st->codec->extradata_size > 4 && st->codec->extradata[0] == 1) {
@@ -273,7 +285,7 @@ defaultcase:
 
 fail:
     av_freep(&s->buf);
-    return AVERROR(EINVAL);
+    return ret;
 }
 
 /* send an rtcp sender report packet */
@@ -567,6 +579,9 @@ static int rtp_write_packet(AVFormatContext *s1, AVPacket *pkt)
     case AV_CODEC_ID_H264:
         ff_rtp_send_h264(s1, pkt->data, size);
         break;
+    case AV_CODEC_ID_H261:
+        ff_rtp_send_h261(s1, pkt->data, size);
+        break;
     case AV_CODEC_ID_H263:
         if (s->flags & FF_RTP_FLAG_RFC2190) {
             int mb_info_size = 0;

libavformat/rtpenc.h

@@ -81,6 +81,7 @@ typedef struct RTPMuxContext RTPMuxContext;
 void ff_rtp_send_data(AVFormatContext *s1, const uint8_t *buf1, int len, int m);
 
 void ff_rtp_send_h264(AVFormatContext *s1, const uint8_t *buf1, int size);
+void ff_rtp_send_h261(AVFormatContext *s1, const uint8_t *buf1, int size);
 void ff_rtp_send_h263(AVFormatContext *s1, const uint8_t *buf1, int size);
 void ff_rtp_send_h263_rfc2190(AVFormatContext *s1, const uint8_t *buf1, int size,
                               const uint8_t *mb_info, int mb_info_size);

libavformat/rtpenc_h261.c

+/*
+ * RTP packetization for H.261 video (RFC 4587)
+ * Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.com>
+ *
+ * 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"
+
+#define RTP_H261_HEADER_SIZE 4
+
+static const uint8_t *find_resync_marker_reverse(const uint8_t *restrict start,
+                                                 const uint8_t *restrict end)
+{
+    const uint8_t *p = end - 1;
+    start += 1; /* Make sure we never return the original start. */
+    for (; p > start; p--) {
+        if (p[0] == 0 && p[1] == 1)
+            return p;
+    }
+    return end;
+}
+
+void ff_rtp_send_h261(AVFormatContext *ctx, const uint8_t *frame_buf, int frame_size)
+{
+    int cur_frame_size;
+    int last_packet_of_frame;
+    RTPMuxContext *rtp_ctx = ctx->priv_data;
+
+    /* use the default 90 KHz time stamp */
+    rtp_ctx->timestamp = rtp_ctx->cur_timestamp;
+
+    /* continue as long as not all frame data is processed */
+    while (frame_size > 0) {
+        /*
+         * encode the H.261 payload header according to section 4.1 of RFC 4587:
+         * (uses 4 bytes between RTP header and H.261 stream per packet)
+         *
+         *    0                   1                   2                   3
+         *    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+         *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+         *   |SBIT |EBIT |I|V| GOBN  |   MBAP  |  QUANT  |  HMVD   |  VMVD   |
+         *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+         *
+         *      Start bit position (SBIT): 3 bits
+         *      End bit position (EBIT): 3 bits
+         *      INTRA-frame encoded data (I): 1 bit
+         *      Motion Vector flag (V): 1 bit
+         *      GOB number (GOBN): 4 bits
+         *      Macroblock address predictor (MBAP): 5 bits
+         *      Quantizer (QUANT): 5 bits
+         *      Horizontal motion vector data (HMVD): 5 bits
+         *      Vertical motion vector data (VMVD): 5 bits
+         */
+        rtp_ctx->buf[0] = 1; /* sbit=0, ebit=0, i=0, v=1 */
+        rtp_ctx->buf[1] = 0; /* gobn=0, mbap=0 */
+        rtp_ctx->buf[2] = 0; /* quant=0, hmvd=5 */
+        rtp_ctx->buf[3] = 0; /* vmvd=0 */
+        if (frame_size < 2 || frame_buf[0] != 0 || frame_buf[1] != 1) {
+            /* A full, correct fix for this would be to make the H261 encoder
+             * support inserting extra GOB headers (triggered by setting e.g.
+             * "-ps 1"), and including information about macroblock boundaries
+             * (such as for h263_rfc2190). */
+            av_log(ctx, AV_LOG_WARNING,
+                   "RTP/H261 packet not cut at a GOB boundary, not signaled correctly\n");
+        }
+
+        cur_frame_size = FFMIN(rtp_ctx->max_payload_size - RTP_H261_HEADER_SIZE, frame_size);
+
+        /* look for a better place to split the frame into packets */
+        if (cur_frame_size < frame_size) {
+            const uint8_t *packet_end = find_resync_marker_reverse(frame_buf,
+                                                                   frame_buf + cur_frame_size);
+            cur_frame_size = packet_end - frame_buf;
+        }
+
+        /* calculate the "marker" bit for the RTP header */
+        last_packet_of_frame = cur_frame_size == frame_size;
+
+        /* complete and send RTP packet */
+        memcpy(&rtp_ctx->buf[RTP_H261_HEADER_SIZE], frame_buf, cur_frame_size);
+        ff_rtp_send_data(ctx, rtp_ctx->buf, RTP_H261_HEADER_SIZE + cur_frame_size, last_packet_of_frame);
+
+        frame_buf  += cur_frame_size;
+        frame_size -= cur_frame_size;
+    }
+}

libavformat/sdp.c

@@ -498,6 +498,20 @@ static char *sdp_write_media_attributes(char *buff, int size, AVCodecContext *c,
                                      payload_type, mode, config ? config : "");
             break;
         }
+        case AV_CODEC_ID_H261:
+        {
+            const char *pic_fmt = NULL;
+            /* only QCIF and CIF are specified as supported in RFC 4587 */
+            if (c->width == 176 && c->height == 144)
+                pic_fmt = "QCIF=1";
+            else if (c->width == 352 && c->height == 288)
+                pic_fmt = "CIF=1";
+            if (payload_type >= RTP_PT_PRIVATE)
+                av_strlcatf(buff, size, "a=rtpmap:%d H261/90000\r\n", payload_type);
+            if (pic_fmt)
+                av_strlcatf(buff, size, "a=fmtp:%d %s\r\n", payload_type, pic_fmt);
+            break;
+        }
         case AV_CODEC_ID_H263:
         case AV_CODEC_ID_H263P:
             /* a=framesize is required by 3GPP TS 26.234 (PSS). It

libavformat/version.h

@@ -30,8 +30,8 @@
 #include "libavutil/version.h"
 
 #define LIBAVFORMAT_VERSION_MAJOR 56
-#define LIBAVFORMAT_VERSION_MINOR  7
-#define LIBAVFORMAT_VERSION_MICRO  2
+#define LIBAVFORMAT_VERSION_MINOR  8
+#define LIBAVFORMAT_VERSION_MICRO  0
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \