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/*
* Shared definitions and helper functions for
* AV1 (de)packetization.
* Copyright (c) 2024 Axis Communications
*
* 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
*/
/**
* @file
* @brief shared defines and functions for AV1 RTP dec/enc
* @author Chris Hodges <chris.hodges@axis.com>
*/
#ifndef AVFORMAT_RTP_AV1_H
#define AVFORMAT_RTP_AV1_H
#include <stdint.h>
#include "libavutil/log.h"
// define a couple of flags and bit fields
#define AV1B_OBU_FORBIDDEN 7
#define AV1F_OBU_FORBIDDEN (1u << AV1B_OBU_FORBIDDEN)
#define AV1S_OBU_TYPE 3
#define AV1M_OBU_TYPE 15
#define AV1B_OBU_EXTENSION_FLAG 2
#define AV1F_OBU_EXTENSION_FLAG (1u << AV1B_OBU_EXTENSION_FLAG)
#define AV1B_OBU_HAS_SIZE_FIELD 1
#define AV1F_OBU_HAS_SIZE_FIELD (1u << AV1B_OBU_HAS_SIZE_FIELD)
#define AV1B_OBU_RESERVED_1BIT 0
#define AV1F_OBU_RESERVED_1BIT (1u << AV1B_OBU_RESERVED_1BIT)
#define AV1B_AGGR_HDR_FRAG_CONT 7
#define AV1F_AGGR_HDR_FRAG_CONT (1u << AV1B_AGGR_HDR_FRAG_CONT)
#define AV1B_AGGR_HDR_LAST_FRAG 6
#define AV1F_AGGR_HDR_LAST_FRAG (1u << AV1B_AGGR_HDR_LAST_FRAG)
#define AV1S_AGGR_HDR_NUM_OBUS 4
#define AV1M_AGGR_HDR_NUM_OBUS 3
#define AV1B_AGGR_HDR_FIRST_PKT 3
#define AV1F_AGGR_HDR_FIRST_PKT (1u << AV1B_AGGR_HDR_FIRST_PKT)
/// calculate number of required LEB bytes for the given length
static inline unsigned int calc_leb_size(uint32_t length) {
unsigned int num_lebs = 0;
do {
num_lebs++;
length >>= 7;
} while (length);
return num_lebs;
}
/// write out variable number of LEB bytes for the given length
static inline unsigned int write_leb(uint8_t *lebptr, uint32_t length) {
unsigned int num_lebs = 0;
do {
num_lebs++;
if (length < 0x80) {
*lebptr = length;
break;
}
*lebptr++ = length | 0x80; // no need to mask out
length >>= 7;
} while (1);
return num_lebs;
}
/// write out fixed number of LEB bytes (may have "unused" bytes)
static inline void write_leb_n(uint8_t *lebptr, uint32_t length, unsigned int num_lebs) {
for (int i = 0; i < num_lebs; i++) {
if (i == num_lebs - 1) {
*lebptr = length & 0x7f;
} else {
*lebptr++ = length | 0x80; // no need to mask out
}
length >>= 7;
}
}
/// securely parse LEB bytes and return the resulting encoded length
static inline unsigned int parse_leb(void *logctx, const uint8_t *buf_ptr,
uint32_t buffer_size, uint32_t *obu_size) {
uint8_t leb128;
unsigned int num_lebs = 0;
*obu_size = 0;
do {
uint32_t leb7;
if (!buffer_size) {
av_log(logctx, AV_LOG_ERROR, "AV1: Out of data in OBU size field AV1 RTP packet\n");
return 0;
}
leb128 = *buf_ptr++;
leb7 = leb128 & 0x7f;
buffer_size--;
/* AV1 spec says that the maximum value returned from leb128 must fit in
* 32 bits, so if the next byte will shift data out, we have some kind
* of violation here. It is legal, though, to have the most significant
* bytes with all zero bits (in the lower 7 bits). */
if (((num_lebs == 4) && (leb7 >= 0x10)) || ((num_lebs > 4) && leb7)) {
av_log(logctx, AV_LOG_ERROR, "AV1: OBU size field exceeds 32 bit in AV1 RTP packet\n");
return 0;
}
if ((num_lebs == 7) && (leb128 >= 0x80)) {
/* leb128 is defined to be up to 8 bytes (why???), 8th byte MUST NOT
* indicate continuation */
av_log(logctx, AV_LOG_ERROR, "AV1: OBU size field consists of too many bytes in AV1 RTP packet\n");
return 0;
}
// shifts >= 32 are undefined in C!
if (num_lebs <= 4) {
*obu_size |= leb7 << (7 * num_lebs);
}
num_lebs++;
} while (leb128 >= 0x80);
return num_lebs;
}
#endif /* AVFORMAT_RTP_AV1_H */
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