| /* |
| * RTP packetization for H.261 video (RFC 4587) |
| * Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.com> |
| * |
| * This file is part of FFmpeg. |
| * |
| * FFmpeg 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" |
| |
| #define RTP_H261_HEADER_SIZE 4 |
| |
| static const uint8_t *find_resync_marker_reverse(const uint8_t *av_restrict start, |
| const uint8_t *av_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; |
| } |
| } |