rtpenc: MP4A-LATM payload support

This is enabled with an AVOption on the RTP muxer. The SDP
generator looks for a latm flag in the rtpflags field.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/Makefile

@@ -545,7 +545,7 @@ OBJS-$(CONFIG_NUT_MUXER)               += mpegaudiodata.o
 OBJS-$(CONFIG_OGG_DEMUXER)             += flacdec.o flacdata.o flac.o \
                                           dirac.o mpeg12data.o
 OBJS-$(CONFIG_OGG_MUXER)               += xiph.o flacdec.o flacdata.o flac.o
-OBJS-$(CONFIG_RTP_MUXER)               += mpegvideo.o xiph.o
+OBJS-$(CONFIG_RTP_MUXER)               += mpeg4audio.o mpegvideo.o xiph.o
 OBJS-$(CONFIG_SPDIF_DEMUXER)           += aacadtsdec.o mpeg4audio.o
 OBJS-$(CONFIG_WEBM_MUXER)              += xiph.o mpeg4audio.o \
                                           flacdec.o flacdata.o flac.o \

libavformat/Makefile

@@ -228,6 +228,7 @@ OBJS-$(CONFIG_RSO_MUXER)                 += rsoenc.o rso.o
 OBJS-$(CONFIG_RPL_DEMUXER)               += rpl.o
 OBJS-$(CONFIG_RTP_MUXER)                 += rtp.o         \
                                             rtpenc_aac.o     \
+                                            rtpenc_latm.o    \
                                             rtpenc_amr.o     \
                                             rtpenc_h263.o    \
                                             rtpenc_mpv.o     \

libavformat/rtpenc.c

@@ -23,11 +23,25 @@
 #include "mpegts.h"
 #include "internal.h"
 #include "libavutil/random_seed.h"
+#include "libavutil/opt.h"
 
 #include "rtpenc.h"
 
 //#define DEBUG
 
+static const AVOption options[] = {
+    { "rtpflags", "RTP muxer flags", offsetof(RTPMuxContext, flags), FF_OPT_TYPE_FLAGS, {.dbl = 0}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "rtpflags" },
+    { "latm", "Use MP4A-LATM packetization instead of MPEG4-GENERIC for AAC", 0, FF_OPT_TYPE_CONST, {.dbl = FF_RTP_FLAG_MP4A_LATM}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "rtpflags" },
+    { NULL },
+};
+
+static const AVClass rtp_muxer_class = {
+    .class_name = "RTP muxer",
+    .item_name  = av_default_item_name,
+    .option     = options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
 #define RTCP_SR_SIZE 28
 
 static int is_supported(enum CodecID id)
@@ -404,7 +418,10 @@ static int rtp_write_packet(AVFormatContext *s1, AVPacket *pkt)
         ff_rtp_send_mpegvideo(s1, pkt->data, size);
         break;
     case CODEC_ID_AAC:
-        ff_rtp_send_aac(s1, pkt->data, size);
+        if (s->flags & FF_RTP_FLAG_MP4A_LATM)
+            ff_rtp_send_latm(s1, pkt->data, size);
+        else
+            ff_rtp_send_aac(s1, pkt->data, size);
         break;
     case CODEC_ID_AMR_NB:
     case CODEC_ID_AMR_WB:
@@ -455,4 +472,5 @@ AVOutputFormat ff_rtp_muxer = {
     rtp_write_header,
     rtp_write_packet,
     rtp_write_trailer,
+    .priv_class = &rtp_muxer_class,
 };

libavformat/rtpenc.h

@@ -25,6 +25,7 @@
 #include "rtp.h"
 
 struct RTPMuxContext {
+    const AVClass *av_class;
     AVFormatContext *ic;
     AVStream *st;
     int payload_type;
@@ -56,15 +57,20 @@ struct RTPMuxContext {
      * (1, 2 or 4)
      */
     int nal_length_size;
+
+    int flags;
 };
 
 typedef struct RTPMuxContext RTPMuxContext;
 
+#define FF_RTP_FLAG_MP4A_LATM 1
+
 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_h263(AVFormatContext *s1, const uint8_t *buf1, int size);
 void ff_rtp_send_aac(AVFormatContext *s1, const uint8_t *buff, int size);
+void ff_rtp_send_latm(AVFormatContext *s1, const uint8_t *buff, int size);
 void ff_rtp_send_amr(AVFormatContext *s1, const uint8_t *buff, int size);
 void ff_rtp_send_mpegvideo(AVFormatContext *s1, const uint8_t *buf1, int size);
 void ff_rtp_send_xiph(AVFormatContext *s1, const uint8_t *buff, int size);

libavformat/rtpenc_latm.c

+/*
+ * RTP Packetization of MPEG-4 Audio (RFC 3016)
+ * Copyright (c) 2011 Juan Carlos Rodriguez <ing.juancarlosrodriguez@hotmail.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.
+ *
+ * FFmpeg 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 FFmpeg; 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"
+
+void ff_rtp_send_latm(AVFormatContext *s1, const uint8_t *buff, int size)
+{
+    /* MP4A-LATM
+     * The RTP payload format specification is described in RFC 3016
+     * The encoding specifications are provided in ISO/IEC 14496-3 */
+
+    RTPMuxContext *s = s1->priv_data;
+    int header_size;
+    int offset = 0;
+    int len    = 0;
+
+    /* skip ADTS header, if present */
+    if ((s1->streams[0]->codec->extradata_size) == 0) {
+        size -= 7;
+        buff += 7;
+    }
+
+    /* PayloadLengthInfo() */
+    header_size = size/0xFF + 1;
+    memset(s->buf, 0xFF, header_size - 1);
+    s->buf[header_size - 1] = size % 0xFF;
+
+    s->timestamp = s->cur_timestamp;
+
+    /* PayloadMux() */
+    while (size > 0) {
+        len   = FFMIN(size, s->max_payload_size - (!offset ? header_size : 0));
+        size -= len;
+        if (!offset) {
+            memcpy(s->buf + header_size, buff, len);
+            ff_rtp_send_data(s1, s->buf, header_size + len, !size);
+        } else {
+            ff_rtp_send_data(s1, buff + offset, len, !size);
+        }
+        offset += len;
+    }
+}

libavformat/sdp.c

@@ -23,7 +23,9 @@
 #include "libavutil/base64.h"
 #include "libavutil/dict.h"
 #include "libavutil/parseutils.h"
+#include "libavutil/opt.h"
 #include "libavcodec/xiph.h"
+#include "libavcodec/mpeg4audio.h"
 #include "avformat.h"
 #include "internal.h"
 #include "avc.h"
@@ -300,6 +302,71 @@ xiph_fail:
     return NULL;
 }
 
+static int latm_context2profilelevel(AVCodecContext *c)
+{
+    /* MP4A-LATM
+     * The RTP payload format specification is described in RFC 3016
+     * The encoding specifications are provided in ISO/IEC 14496-3 */
+
+    int profile_level = 0x2B;
+
+    /* TODO: AAC Profile only supports AAC LC Object Type.
+     * Different Object Types should implement different Profile Levels */
+
+    if (c->sample_rate <= 24000) {
+        if (c->channels <= 2)
+            profile_level = 0x28; // AAC Profile, Level 1
+    } else if (c->sample_rate <= 48000) {
+        if (c->channels <= 2) {
+            profile_level = 0x29; // AAC Profile, Level 2
+        } else if (c->channels <= 5) {
+            profile_level = 0x2A; // AAC Profile, Level 4
+        }
+    } else if (c->sample_rate <= 96000) {
+        if (c->channels <= 5) {
+            profile_level = 0x2B; // AAC Profile, Level 5
+        }
+    }
+
+    return profile_level;
+}
+
+static char *latm_context2config(AVCodecContext *c)
+{
+    /* MP4A-LATM
+     * The RTP payload format specification is described in RFC 3016
+     * The encoding specifications are provided in ISO/IEC 14496-3 */
+
+    uint8_t config_byte[6];
+    int rate_index;
+    char *config;
+
+    for (rate_index = 0; rate_index < 16; rate_index++)
+        if (ff_mpeg4audio_sample_rates[rate_index] == c->sample_rate)
+            break;
+    if (rate_index == 16) {
+        av_log(c, AV_LOG_ERROR, "Unsupported sample rate\n");
+        return NULL;
+    }
+
+    config_byte[0] = 0x40;
+    config_byte[1] = 0;
+    config_byte[2] = 0x20 | rate_index;
+    config_byte[3] = c->channels << 4;
+    config_byte[4] = 0x3f;
+    config_byte[5] = 0xc0;
+
+    config = av_malloc(6*2+1);
+    if (!config) {
+        av_log(c, AV_LOG_ERROR, "Cannot allocate memory for the config info.\n");
+        return NULL;
+    }
+    ff_data_to_hex(config, config_byte, 6, 1);
+    config[12] = 0;
+
+    return config;
+}
+
 static char *sdp_write_media_attributes(char *buff, int size, AVCodecContext *c, int payload_type, AVFormatContext *fmt)
 {
     char *config = NULL;
@@ -335,6 +402,16 @@ static char *sdp_write_media_attributes(char *buff, int size, AVCodecContext *c,
                                      payload_type, config ? config : "");
             break;
         case CODEC_ID_AAC:
+            if (fmt && fmt->oformat->priv_class &&
+                av_opt_flag_is_set(fmt->priv_data, "rtpflags", "latm")) {
+                config = latm_context2config(c);
+                if (!config)
+                    return NULL;
+                av_strlcatf(buff, size, "a=rtpmap:%d MP4A-LATM/%d/%d\r\n"
+                                        "a=fmtp:%d profile-level-id=%d;cpresent=0;config=%s\r\n",
+                                         payload_type, c->sample_rate, c->channels,
+                                         payload_type, latm_context2profilelevel(c), config);
+            } else {
             if (c->extradata_size) {
                 config = extradata2config(c);
             } else {
@@ -353,6 +430,7 @@ static char *sdp_write_media_attributes(char *buff, int size, AVCodecContext *c,
                                     "indexdeltalength=3%s\r\n",
                                      payload_type, c->sample_rate, c->channels,
                                      payload_type, config);
+            }
             break;
         case CODEC_ID_PCM_S16BE:
             if (payload_type >= RTP_PT_PRIVATE)

libavformat/version.h

@@ -25,7 +25,7 @@
 
 #define LIBAVFORMAT_VERSION_MAJOR 53
 #define LIBAVFORMAT_VERSION_MINOR  1
-#define LIBAVFORMAT_VERSION_MICRO  0
+#define LIBAVFORMAT_VERSION_MICRO  1
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \