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/*
* RTP parser for H.261 payload format (RFC 4587)
* Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.com>
*
* 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_free_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),
.free = h261_free_context,
.parse_packet = h261_handle_packet,
.static_payload_id = 31,
};
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