From a505c0d7373336a4cc5aa2022111c46bdd388b1f Mon Sep 17 00:00:00 2001 From: Thomas Volkert Date: Sat, 6 Dec 2014 19:54:07 +0100 Subject: rtp: Initial H.261 support MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The packetizer only supports splitting at GOB headers - if such aren't available frequently enough, it splits at any random byte offset (not at a macroblock boundary either, which would be allowed by the spec) and sends a payload header pretend that it starts with a GOB header. As long as a receiver doesn't try to handle such cases cleverly but just drops broken frames, this shouldn't matter too much in practice. Signed-off-by: Martin Storsjö --- libavformat/rtpdec_h261.c | 202 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 202 insertions(+) create mode 100644 libavformat/rtpdec_h261.c (limited to 'libavformat/rtpdec_h261.c') diff --git a/libavformat/rtpdec_h261.c b/libavformat/rtpdec_h261.c new file mode 100644 index 0000000000..4988300831 --- /dev/null +++ b/libavformat/rtpdec_h261.c @@ -0,0 +1,202 @@ +/* + * 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 "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 PayloadContext *h261_new_context(void) +{ + return av_mallocz(sizeof(PayloadContext)); +} + +static void h261_free_dyn_buffer(AVIOContext **dyn_buf) +{ + uint8_t *ptr_dyn_buffer; + avio_close_dyn_buf(*dyn_buf, &ptr_dyn_buffer); + av_free(ptr_dyn_buffer); + *dyn_buf = NULL; +} + +static av_cold void h261_free_context(PayloadContext *pl_ctx) +{ + /* return if context is invalid */ + if (!pl_ctx) + return; + + /* free buffer if it is valid */ + if (pl_ctx->buf) { + h261_free_dyn_buffer(&pl_ctx->buf); + } + + /* free context */ + av_free(pl_ctx); +} + +static av_cold int h261_init(AVFormatContext *ctx, int st_index, + PayloadContext *data) +{ + if (st_index < 0) + return 0; + + ctx->streams[st_index]->need_parsing = AVSTREAM_PARSE_FULL; + + return 0; +} + +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) { + h261_free_dyn_buffer(&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, + .init = h261_init, + .alloc = h261_new_context, + .free = h261_free_context, + .parse_packet = h261_handle_packet, + .static_payload_id = 31, +}; -- cgit v1.2.1