/* * RTP parser for H.261 payload format (RFC 4587) * Copyright (c) 2014 Thomas Volkert * * 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 "libavcodec/get_bits.h" #include "avformat.h" #include "avio_internal.h" #include "rtpdec_formats.h" #define RTP_H261_PAYLOAD_HEADER_SIZE 4 struct PayloadContext { AVIOContext *buf; uint8_t endbyte; int endbyte_bits; uint32_t timestamp; }; static av_cold void h261_close_context(PayloadContext *pl_ctx) { /* return if context is invalid */ if (!pl_ctx) return; /* free buffer if it is valid */ ffio_free_dyn_buf(&pl_ctx->buf); } static int h261_handle_packet(AVFormatContext *ctx, PayloadContext *rtp_h261_ctx, AVStream *st, AVPacket *pkt, uint32_t *timestamp, const uint8_t *buf, int len, uint16_t seq, int flags) { int sbit, ebit, gobn, mbap, quant; int res; /* drop data of previous packets in case of non-continuous (lossy) packet stream */ if (rtp_h261_ctx->buf && rtp_h261_ctx->timestamp != *timestamp) { ffio_free_dyn_buf(&rtp_h261_ctx->buf); rtp_h261_ctx->endbyte_bits = 0; } /* sanity check for size of input packet: 1 byte payload at least */ if (len < RTP_H261_PAYLOAD_HEADER_SIZE + 1) { av_log(ctx, AV_LOG_ERROR, "Too short RTP/H.261 packet, got %d bytes\n", len); return AVERROR_INVALIDDATA; } /* * decode 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 */ sbit = (buf[0] >> 5) & 0x07; ebit = (buf[0] >> 2) & 0x07; gobn = (buf[1] >> 4) & 0x0f; mbap = ((buf[1] << 1) & 0x1e) | ((buf[2] >> 7) & 0x01); quant = (buf[2] >> 2) & 0x1f; /* pass the H.261 payload header and continue with the actual payload */ buf += RTP_H261_PAYLOAD_HEADER_SIZE; len -= RTP_H261_PAYLOAD_HEADER_SIZE; /* start frame buffering with new dynamic buffer */ if (!rtp_h261_ctx->buf) { /* sanity check: a new frame starts with gobn=0, sbit=0, mbap=0, quant=0 */ if (!gobn && !sbit && !mbap && !quant) { res = avio_open_dyn_buf(&rtp_h261_ctx->buf); if (res < 0) return res; /* update the timestamp in the frame packet with the one from the RTP packet */ rtp_h261_ctx->timestamp = *timestamp; } else { /* frame not started yet, need more packets */ return AVERROR(EAGAIN); } } /* do the "byte merging" at the boundaries of two consecutive frame fragments */ if (rtp_h261_ctx->endbyte_bits || sbit) { if (rtp_h261_ctx->endbyte_bits == sbit) { rtp_h261_ctx->endbyte |= buf[0] & (0xff >> sbit); rtp_h261_ctx->endbyte_bits = 0; buf++; len--; avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte); } else { /* ebit/sbit values inconsistent, assuming packet loss */ GetBitContext gb; init_get_bits(&gb, buf, len*8 - ebit); skip_bits(&gb, sbit); if (rtp_h261_ctx->endbyte_bits) { rtp_h261_ctx->endbyte |= get_bits(&gb, 8 - rtp_h261_ctx->endbyte_bits); avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte); } while (get_bits_left(&gb) >= 8) avio_w8(rtp_h261_ctx->buf, get_bits(&gb, 8)); rtp_h261_ctx->endbyte_bits = get_bits_left(&gb); if (rtp_h261_ctx->endbyte_bits) rtp_h261_ctx->endbyte = get_bits(&gb, rtp_h261_ctx->endbyte_bits) << (8 - rtp_h261_ctx->endbyte_bits); ebit = 0; len = 0; } } if (ebit) { if (len > 0) avio_write(rtp_h261_ctx->buf, buf, len - 1); rtp_h261_ctx->endbyte_bits = 8 - ebit; rtp_h261_ctx->endbyte = buf[len - 1] & (0xff << ebit); } else { avio_write(rtp_h261_ctx->buf, buf, len); } /* RTP marker bit means: last fragment of current frame was received; otherwise, an additional fragment is needed for the current frame */ if (!(flags & RTP_FLAG_MARKER)) return AVERROR(EAGAIN); /* write the completed last byte from the "byte merging" */ if (rtp_h261_ctx->endbyte_bits) avio_w8(rtp_h261_ctx->buf, rtp_h261_ctx->endbyte); rtp_h261_ctx->endbyte_bits = 0; /* close frame buffering and create resulting A/V packet */ res = ff_rtp_finalize_packet(pkt, &rtp_h261_ctx->buf, st->index); if (res < 0) return res; return 0; } RTPDynamicProtocolHandler ff_h261_dynamic_handler = { .enc_name = "H261", .codec_type = AVMEDIA_TYPE_VIDEO, .codec_id = AV_CODEC_ID_H261, .need_parsing = AVSTREAM_PARSE_FULL, .priv_data_size = sizeof(PayloadContext), .close = h261_close_context, .parse_packet = h261_handle_packet, .static_payload_id = 31, };