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/*
* 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 H.261 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/H.261 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;
}
}
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