经常遇到ivf格式,下面看看它的头:
typedef struct ivf_header {
// 0-3 固定的'DKIF'字符串
// 4-5 version,应该为0
// 6-7 header的字节长度
// 8-11 编码器的FourCC (e.g., 'VP80')
// 12-13 width in pixels
// 14-15 height in pixels
// 16-19 framerate,单位为(1/timescale)
// 20-23 timescale
// 24-27 帧的个数
// 28-31 unused
uint32_t signature;
uint16_t version;
uint16_t lenght;
uint32_t fourcc;
uint16_t width;
uint16_t height;
uint32_t framerate;
uint32_t timescale;
uint32_t frame_count;
uint32_t unused;
} ivf_header;
所以整个头文件大小是:32个字节。
另外每一帧还有4+8=12字节的头。
关于上述解析,ffmpeg-ivfdec.c中有:
/*
* Copyright (c) 2010 David Conrad
*
* 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 "avformat.h"
#include "internal.h"
#include "riff.h"
#include "libavutil/intreadwrite.h"
static int probe(const AVProbeData *p)
{
if (AV_RL32(p->buf) == MKTAG('D','K','I','F')
&& !AV_RL16(p->buf+4) && AV_RL16(p->buf+6) == 32)
return AVPROBE_SCORE_MAX-2;
return 0;
}
static int read_header(AVFormatContext *s)
{
AVStream *st;
AVRational time_base;
avio_rl32(s->pb); // DKIF
avio_rl16(s->pb); // version
avio_rl16(s->pb); // header size
st = avformat_new_stream(s, NULL);
if (!st)
return AVERROR(ENOMEM);
st->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
st->codecpar->codec_tag = avio_rl32(s->pb);
st->codecpar->codec_id = ff_codec_get_id(ff_codec_bmp_tags, st->codecpar->codec_tag);
st->codecpar->width = avio_rl16(s->pb);
st->codecpar->height = avio_rl16(s->pb);
time_base.den = avio_rl32(s->pb);
time_base.num = avio_rl32(s->pb);
st->duration = avio_rl32(s->pb);
avio_skip(s->pb, 4); // unused
st->need_parsing = AVSTREAM_PARSE_HEADERS;
//如果这两个有问题,一般会失败,所以ivf必须要填写
if (!time_base.den || !time_base.num) {
av_log(s, AV_LOG_ERROR, "Invalid frame rate\n");
return AVERROR_INVALIDDATA;
}
avpriv_set_pts_info(st, 64, time_base.num, time_base.den);
return 0;
}
static int read_packet(AVFormatContext *s, AVPacket *pkt)
{
int ret, size = avio_rl32(s->pb);
int64_t pts = avio_rl64(s->pb);
ret = av_get_packet(s->pb, pkt, size);
pkt->stream_index = 0;
pkt->pts = pts;
pkt->pos -= 12;
return ret;
}
AVInputFormat ff_ivf_demuxer = {
.name = "ivf",
.long_name = NULL_IF_CONFIG_SMALL("On2 IVF"),
.read_probe = probe,
.read_header = read_header,
.read_packet = read_packet,
.flags = AVFMT_GENERIC_INDEX,
.codec_tag = (const AVCodecTag* const []){
ff_codec_bmp_tags, 0 },
};