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103 lines
4.2 KiB
C
103 lines
4.2 KiB
C
/*
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* RTP packetization for H.261 video (RFC 4587)
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* Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.com>
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*
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* This file is part of Libav.
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*
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* Libav is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* Libav is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with Libav; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include "avformat.h"
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#include "rtpenc.h"
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#define RTP_H261_HEADER_SIZE 4
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static const uint8_t *find_resync_marker_reverse(const uint8_t *restrict start,
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const uint8_t *restrict end)
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{
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const uint8_t *p = end - 1;
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start += 1; /* Make sure we never return the original start. */
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for (; p > start; p--) {
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if (p[0] == 0 && p[1] == 1)
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return p;
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}
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return end;
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}
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void ff_rtp_send_h261(AVFormatContext *ctx, const uint8_t *frame_buf, int frame_size)
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{
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int cur_frame_size;
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int last_packet_of_frame;
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RTPMuxContext *rtp_ctx = ctx->priv_data;
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/* use the default 90 KHz time stamp */
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rtp_ctx->timestamp = rtp_ctx->cur_timestamp;
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/* continue as long as not all frame data is processed */
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while (frame_size > 0) {
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/*
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* encode the H.261 payload header according to section 4.1 of RFC 4587:
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* (uses 4 bytes between RTP header and H.261 stream per packet)
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*
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* 0 1 2 3
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* 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
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* |SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*
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* Start bit position (SBIT): 3 bits
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* End bit position (EBIT): 3 bits
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* INTRA-frame encoded data (I): 1 bit
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* Motion Vector flag (V): 1 bit
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* GOB number (GOBN): 4 bits
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* Macroblock address predictor (MBAP): 5 bits
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* Quantizer (QUANT): 5 bits
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* Horizontal motion vector data (HMVD): 5 bits
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* Vertical motion vector data (VMVD): 5 bits
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*/
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rtp_ctx->buf[0] = 1; /* sbit=0, ebit=0, i=0, v=1 */
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rtp_ctx->buf[1] = 0; /* gobn=0, mbap=0 */
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rtp_ctx->buf[2] = 0; /* quant=0, hmvd=5 */
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rtp_ctx->buf[3] = 0; /* vmvd=0 */
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if (frame_size < 2 || frame_buf[0] != 0 || frame_buf[1] != 1) {
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/* A full, correct fix for this would be to make the H.261 encoder
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* support inserting extra GOB headers (triggered by setting e.g.
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* "-ps 1"), and including information about macroblock boundaries
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* (such as for h263_rfc2190). */
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av_log(ctx, AV_LOG_WARNING,
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"RTP/H.261 packet not cut at a GOB boundary, not signaled correctly\n");
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}
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cur_frame_size = FFMIN(rtp_ctx->max_payload_size - RTP_H261_HEADER_SIZE, frame_size);
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/* look for a better place to split the frame into packets */
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if (cur_frame_size < frame_size) {
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const uint8_t *packet_end = find_resync_marker_reverse(frame_buf,
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frame_buf + cur_frame_size);
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cur_frame_size = packet_end - frame_buf;
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}
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/* calculate the "marker" bit for the RTP header */
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last_packet_of_frame = cur_frame_size == frame_size;
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/* complete and send RTP packet */
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memcpy(&rtp_ctx->buf[RTP_H261_HEADER_SIZE], frame_buf, cur_frame_size);
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ff_rtp_send_data(ctx, rtp_ctx->buf, RTP_H261_HEADER_SIZE + cur_frame_size, last_packet_of_frame);
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frame_buf += cur_frame_size;
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frame_size -= cur_frame_size;
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}
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}
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