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/rtpenc_h261.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 102 insertions(+) create mode 100644 libavformat/rtpenc_h261.c (limited to 'libavformat/rtpenc_h261.c') diff --git a/libavformat/rtpenc_h261.c b/libavformat/rtpenc_h261.c new file mode 100644 index 0000000000..514e7bf9ca --- /dev/null +++ b/libavformat/rtpenc_h261.c @@ -0,0 +1,102 @@ +/* + * RTP packetization for H.261 video (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 "avformat.h" +#include "rtpenc.h" + +#define RTP_H261_HEADER_SIZE 4 + +static const uint8_t *find_resync_marker_reverse(const uint8_t *restrict start, + const uint8_t *restrict end) +{ + const uint8_t *p = end - 1; + start += 1; /* Make sure we never return the original start. */ + for (; p > start; p--) { + if (p[0] == 0 && p[1] == 1) + return p; + } + return end; +} + +void ff_rtp_send_h261(AVFormatContext *ctx, const uint8_t *frame_buf, int frame_size) +{ + int cur_frame_size; + int last_packet_of_frame; + RTPMuxContext *rtp_ctx = ctx->priv_data; + + /* use the default 90 KHz time stamp */ + rtp_ctx->timestamp = rtp_ctx->cur_timestamp; + + /* continue as long as not all frame data is processed */ + while (frame_size > 0) { + /* + * encode 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 + */ + rtp_ctx->buf[0] = 1; /* sbit=0, ebit=0, i=0, v=1 */ + rtp_ctx->buf[1] = 0; /* gobn=0, mbap=0 */ + rtp_ctx->buf[2] = 0; /* quant=0, hmvd=5 */ + rtp_ctx->buf[3] = 0; /* vmvd=0 */ + if (frame_size < 2 || frame_buf[0] != 0 || frame_buf[1] != 1) { + /* A full, correct fix for this would be to make the H261 encoder + * support inserting extra GOB headers (triggered by setting e.g. + * "-ps 1"), and including information about macroblock boundaries + * (such as for h263_rfc2190). */ + av_log(ctx, AV_LOG_WARNING, + "RTP/H261 packet not cut at a GOB boundary, not signaled correctly\n"); + } + + cur_frame_size = FFMIN(rtp_ctx->max_payload_size - RTP_H261_HEADER_SIZE, frame_size); + + /* look for a better place to split the frame into packets */ + if (cur_frame_size < frame_size) { + const uint8_t *packet_end = find_resync_marker_reverse(frame_buf, + frame_buf + cur_frame_size); + cur_frame_size = packet_end - frame_buf; + } + + /* calculate the "marker" bit for the RTP header */ + last_packet_of_frame = cur_frame_size == frame_size; + + /* complete and send RTP packet */ + memcpy(&rtp_ctx->buf[RTP_H261_HEADER_SIZE], frame_buf, cur_frame_size); + ff_rtp_send_data(ctx, rtp_ctx->buf, RTP_H261_HEADER_SIZE + cur_frame_size, last_packet_of_frame); + + frame_buf += cur_frame_size; + frame_size -= cur_frame_size; + } +} -- cgit v1.2.3