blob: 22461ca25becf0d866deab5071bfaa09a53a5e3e
| 1 | /* |
| 2 | * RTP packetization for H.261 video (RFC 4587) |
| 3 | * Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.com> |
| 4 | * |
| 5 | * This file is part of FFmpeg. |
| 6 | * |
| 7 | * FFmpeg is free software; you can redistribute it and/or |
| 8 | * modify it under the terms of the GNU Lesser General Public |
| 9 | * License as published by the Free Software Foundation; either |
| 10 | * version 2.1 of the License, or (at your option) any later version. |
| 11 | * |
| 12 | * FFmpeg is distributed in the hope that it will be useful, |
| 13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 15 | * Lesser General Public License for more details. |
| 16 | * |
| 17 | * You should have received a copy of the GNU Lesser General Public |
| 18 | * License along with FFmpeg; if not, write to the Free Software |
| 19 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 20 | */ |
| 21 | |
| 22 | #include "avformat.h" |
| 23 | #include "rtpenc.h" |
| 24 | |
| 25 | #define RTP_H261_HEADER_SIZE 4 |
| 26 | |
| 27 | static const uint8_t *find_resync_marker_reverse(const uint8_t *av_restrict start, |
| 28 | const uint8_t *av_restrict end) |
| 29 | { |
| 30 | const uint8_t *p = end - 1; |
| 31 | start += 1; /* Make sure we never return the original start. */ |
| 32 | for (; p > start; p--) { |
| 33 | if (p[0] == 0 && p[1] == 1) |
| 34 | return p; |
| 35 | } |
| 36 | return end; |
| 37 | } |
| 38 | |
| 39 | void ff_rtp_send_h261(AVFormatContext *ctx, const uint8_t *frame_buf, int frame_size) |
| 40 | { |
| 41 | int cur_frame_size; |
| 42 | int last_packet_of_frame; |
| 43 | RTPMuxContext *rtp_ctx = ctx->priv_data; |
| 44 | |
| 45 | /* use the default 90 KHz time stamp */ |
| 46 | rtp_ctx->timestamp = rtp_ctx->cur_timestamp; |
| 47 | |
| 48 | /* continue as long as not all frame data is processed */ |
| 49 | while (frame_size > 0) { |
| 50 | /* |
| 51 | * encode the H.261 payload header according to section 4.1 of RFC 4587: |
| 52 | * (uses 4 bytes between RTP header and H.261 stream per packet) |
| 53 | * |
| 54 | * 0 1 2 3 |
| 55 | * 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 |
| 56 | * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| 57 | * |SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD | |
| 58 | * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| 59 | * |
| 60 | * Start bit position (SBIT): 3 bits |
| 61 | * End bit position (EBIT): 3 bits |
| 62 | * INTRA-frame encoded data (I): 1 bit |
| 63 | * Motion Vector flag (V): 1 bit |
| 64 | * GOB number (GOBN): 4 bits |
| 65 | * Macroblock address predictor (MBAP): 5 bits |
| 66 | * Quantizer (QUANT): 5 bits |
| 67 | * Horizontal motion vector data (HMVD): 5 bits |
| 68 | * Vertical motion vector data (VMVD): 5 bits |
| 69 | */ |
| 70 | rtp_ctx->buf[0] = 1; /* sbit=0, ebit=0, i=0, v=1 */ |
| 71 | rtp_ctx->buf[1] = 0; /* gobn=0, mbap=0 */ |
| 72 | rtp_ctx->buf[2] = 0; /* quant=0, hmvd=5 */ |
| 73 | rtp_ctx->buf[3] = 0; /* vmvd=0 */ |
| 74 | if (frame_size < 2 || frame_buf[0] != 0 || frame_buf[1] != 1) { |
| 75 | /* A full, correct fix for this would be to make the H.261 encoder |
| 76 | * support inserting extra GOB headers (triggered by setting e.g. |
| 77 | * "-ps 1"), and including information about macroblock boundaries |
| 78 | * (such as for h263_rfc2190). */ |
| 79 | av_log(ctx, AV_LOG_WARNING, |
| 80 | "RTP/H.261 packet not cut at a GOB boundary, not signaled correctly\n"); |
| 81 | } |
| 82 | |
| 83 | cur_frame_size = FFMIN(rtp_ctx->max_payload_size - RTP_H261_HEADER_SIZE, frame_size); |
| 84 | |
| 85 | /* look for a better place to split the frame into packets */ |
| 86 | if (cur_frame_size < frame_size) { |
| 87 | const uint8_t *packet_end = find_resync_marker_reverse(frame_buf, |
| 88 | frame_buf + cur_frame_size); |
| 89 | cur_frame_size = packet_end - frame_buf; |
| 90 | } |
| 91 | |
| 92 | /* calculate the "marker" bit for the RTP header */ |
| 93 | last_packet_of_frame = cur_frame_size == frame_size; |
| 94 | |
| 95 | /* complete and send RTP packet */ |
| 96 | memcpy(&rtp_ctx->buf[RTP_H261_HEADER_SIZE], frame_buf, cur_frame_size); |
| 97 | ff_rtp_send_data(ctx, rtp_ctx->buf, RTP_H261_HEADER_SIZE + cur_frame_size, last_packet_of_frame); |
| 98 | |
| 99 | frame_buf += cur_frame_size; |
| 100 | frame_size -= cur_frame_size; |
| 101 | } |
| 102 | } |
| 103 |