| 1 | /* |
| 2 | * RTP parser for H.261 payload format (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 "rtpdec_formats.h" |
| 24 | #include "libavcodec/get_bits.h" |
| 25 | |
| 26 | #define RTP_H261_PAYLOAD_HEADER_SIZE 4 |
| 27 | |
| 28 | struct PayloadContext { |
| 29 | AVIOContext *buf; |
| 30 | uint8_t endbyte; |
| 31 | int endbyte_bits; |
| 32 | uint32_t timestamp; |
| 33 | }; |
| 34 | |
| 35 | static av_cold PayloadContext *h261_new_context(void) |
| 36 | { |
| 37 | return av_mallocz(sizeof(PayloadContext)); |
| 38 | } |
| 39 | |
| 40 | static void h261_free_dyn_buffer(AVIOContext **dyn_buf) |
| 41 | { |
| 42 | uint8_t *ptr_dyn_buffer; |
| 43 | avio_close_dyn_buf(*dyn_buf, &ptr_dyn_buffer); |
| 44 | av_free(ptr_dyn_buffer); |
| 45 | *dyn_buf = NULL; |
| 46 | } |
| 47 | |
| 48 | static av_cold void h261_free_context(PayloadContext *pl_ctx) |
| 49 | { |
| 50 | /* return if context is invalid */ |
| 51 | if (!pl_ctx) |
| 52 | return; |
| 53 | |
| 54 | /* free buffer if it is valid */ |
| 55 | if (pl_ctx->buf) { |
| 56 | h261_free_dyn_buffer(&pl_ctx->buf); |
| 57 | } |
| 58 | |
| 59 | /* free context */ |
| 60 | av_free(pl_ctx); |
| 61 | } |
| 62 | |
| 63 | static av_cold int h261_init(AVFormatContext *ctx, int st_index, |
| 64 | PayloadContext *data) |
| 65 | { |
| 66 | //av_log(ctx, AV_LOG_DEBUG, "h261_init() for stream %d\n", st_index); |
| 67 | |
| 68 | if (st_index < 0) |
| 69 | return 0; |
| 70 | |
| 71 | ctx->streams[st_index]->need_parsing = AVSTREAM_PARSE_FULL; |
| 72 | |
| 73 | return 0; |
| 74 | } |
| 75 | |
| 76 | int ff_h261_handle_packet(AVFormatContext *ctx, PayloadContext *data, |
| 77 | AVStream *st, AVPacket *pkt, uint32_t *timestamp, |
| 78 | const uint8_t *buf, int len, uint16_t seq, int flags) |
| 79 | { |
| 80 | int sbit, ebit, gobn, mbap, quant; |
| 81 | int res; |
| 82 | |
| 83 | /* drop data of previous packets in case of non-continuous (loss) packet stream */ |
| 84 | if (data->buf && data->timestamp != *timestamp) { |
| 85 | h261_free_dyn_buffer(&data->buf); |
| 86 | } |
| 87 | |
| 88 | /* sanity check for size of input packet: 1 byte payload at least */ |
| 89 | if (len < RTP_H261_PAYLOAD_HEADER_SIZE + 1) { |
| 90 | av_log(ctx, AV_LOG_ERROR, "Too short RTP/H.261 packet, got %d bytes\n", len); |
| 91 | return AVERROR_INVALIDDATA; |
| 92 | } |
| 93 | |
| 94 | /* |
| 95 | decode the H.261 payload header according to section 4.1 of RFC 4587: |
| 96 | (uses 4 bytes between RTP header and H.261 stream per packet) |
| 97 | |
| 98 | 0 1 2 3 |
| 99 | 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 |
| 100 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| 101 | |SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD | |
| 102 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| 103 | |
| 104 | Start bit position (SBIT): 3 bits |
| 105 | End bit position (EBIT): 3 bits |
| 106 | INTRA-frame encoded data (I): 1 bit |
| 107 | Motion Vector flag (V): 1 bit |
| 108 | GOB number (GOBN): 4 bits |
| 109 | Macroblock address predictor (MBAP): 5 bits |
| 110 | Quantizer (QUANT): 5 bits |
| 111 | Horizontal motion vector data (HMVD): 5 bits |
| 112 | Vertical motion vector data (VMVD): 5 bits |
| 113 | |
| 114 | */ |
| 115 | sbit = (buf[0] >> 5) & 0x07; |
| 116 | ebit = (buf[0] >> 2) & 0x07; |
| 117 | gobn = (buf[1] >> 4) & 0x0f; |
| 118 | mbap = ((buf[1] << 1) & 0x1e) | ((buf[2] >> 7) & 0x01); |
| 119 | quant = (buf[2] >> 2) & 0x1f; |
| 120 | |
| 121 | /* pass the H.261 payload header and continue with the actual payload */ |
| 122 | buf += RTP_H261_PAYLOAD_HEADER_SIZE; |
| 123 | len -= RTP_H261_PAYLOAD_HEADER_SIZE; |
| 124 | |
| 125 | /* start frame buffering with new dynamic buffer */ |
| 126 | if (!data->buf) { |
| 127 | /* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, uqnat=0 */ |
| 128 | if (!gobn && !sbit && !mbap && !quant){ |
| 129 | res = avio_open_dyn_buf(&data->buf); |
| 130 | if (res < 0) |
| 131 | return res; |
| 132 | /* update the timestamp in the frame packet with the one from the RTP packet */ |
| 133 | data->timestamp = *timestamp; |
| 134 | } else { |
| 135 | /* frame not started yet, need more packets */ |
| 136 | return AVERROR(EAGAIN); |
| 137 | } |
| 138 | } |
| 139 | |
| 140 | /* do the "byte merging" at the boundaries of two consecutive frame fragments */ |
| 141 | if (data->endbyte_bits || sbit) { |
| 142 | if (data->endbyte_bits == sbit) { |
| 143 | data->endbyte |= buf[0] & (0xff >> sbit); |
| 144 | data->endbyte_bits = 0; |
| 145 | buf++; |
| 146 | len--; |
| 147 | avio_w8(data->buf, data->endbyte); |
| 148 | } else { |
| 149 | /* ebit/sbit values inconsistent, assuming packet loss */ |
| 150 | GetBitContext gb; |
| 151 | init_get_bits(&gb, buf, len*8 - ebit); |
| 152 | skip_bits(&gb, sbit); |
| 153 | if (data->endbyte_bits) { |
| 154 | data->endbyte |= get_bits(&gb, 8 - data->endbyte_bits); |
| 155 | avio_w8(data->buf, data->endbyte); |
| 156 | } |
| 157 | while (get_bits_left(&gb) >= 8) |
| 158 | avio_w8(data->buf, get_bits(&gb, 8)); |
| 159 | data->endbyte_bits = get_bits_left(&gb); |
| 160 | if (data->endbyte_bits) |
| 161 | data->endbyte = get_bits(&gb, data->endbyte_bits) << |
| 162 | (8 - data->endbyte_bits); |
| 163 | ebit = 0; |
| 164 | len = 0; |
| 165 | } |
| 166 | } |
| 167 | if (ebit) { |
| 168 | if (len > 0) |
| 169 | avio_write(data->buf, buf, len - 1); |
| 170 | data->endbyte_bits = 8 - ebit; |
| 171 | data->endbyte = buf[len - 1] & (0xff << ebit); |
| 172 | } else { |
| 173 | avio_write(data->buf, buf, len); |
| 174 | } |
| 175 | |
| 176 | /* RTP marker bit means: last fragment of current frame was received; |
| 177 | otherwise, an additional fragment is needed for the current frame */ |
| 178 | if (!(flags & RTP_FLAG_MARKER)) |
| 179 | return AVERROR(EAGAIN); |
| 180 | |
| 181 | /* write the completed last byte from the "byte merging" */ |
| 182 | if (data->endbyte_bits) |
| 183 | avio_w8(data->buf, data->endbyte); |
| 184 | data->endbyte_bits = 0; |
| 185 | |
| 186 | /* close frame buffering and create resulting A/V packet */ |
| 187 | res = ff_rtp_finalize_packet(pkt, &data->buf, st->index); |
| 188 | if (res < 0) |
| 189 | return res; |
| 190 | |
| 191 | return 0; |
| 192 | } |
| 193 | |
| 194 | RTPDynamicProtocolHandler ff_h261_dynamic_handler = { |
| 195 | .enc_name = "H261", |
| 196 | .codec_type = AVMEDIA_TYPE_VIDEO, |
| 197 | .codec_id = AV_CODEC_ID_H261, |
| 198 | .init = h261_init, |
| 199 | .parse_packet = ff_h261_handle_packet, |
| 200 | .alloc = h261_new_context, |
| 201 | .free = h261_free_context, |
| 202 | .static_payload_id = 31, |
| 203 | }; |