| /* |
| * RTP parser for H.261 payload format (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 "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, |
| }; |
