如何进行FFmpeg H264码流分析播放

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如何进行FFmpeg H264码流分析播放

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1）h364_probe函数剖析

如何进行FFmpeg H264码流分析播放

函数调用
avformat_open_input
s->iformat->read_header(s)
函数说明
/**
Read the format header and initialize the AVFormatContext
structure. Return 0 if OK. 'avformat_new_stream' should be
called to create new streams.
/
int (read_header)(struct AVFormatContext *);
从read_header函数调用，去探测h364的码流格式
代码说明
static int h364_probe(AVProbeData *p)
{
uint32_t code = -1; // code = 0xffffffff
int sps = 0, pps = 0, idr = 0, res = 0, sli = 0;
int i, ret;
int pps_ids[MAX_PPS_COUNT+1] = {0};
int sps_ids[MAX_SPS_COUNT+1] = {0};
unsigned pps_id, sps_id;
GetBitContext gb;
for (i = 0; i + 2 < p->buf_size; i++) {
code = (code << 8) + p->buf[i];
//分离出NAL起始码00 00 00 01 分析出NAL类型
if ((code & 0xffffff00) == 0x100) {
int ref_idc = (code >> 5) & 3;
int type = code & 0x1F;
static const int8_t ref_zero[] = {
2, 0, 0, 0, 0, -1, 1, -1,
-1, 1, 1, 1, 1, -1, 2, 2,
2, 2, 2, 0, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2
};

if (code & 0x80) // forbidden_bit
return 0;

if (ref_zero[type] == 1 && ref_idc)
return 0;
if (ref_zero[type] == -1 && !ref_idc)
return 0;
if (ref_zero[type] == 2) {
if (!(code == 0x100 && !p->buf[i + 1] && !p->buf[i + 2]))
res++;
}

ret = init_get_bits8(&gb, p->buf + i + 1, p->buf_size - i - 1);
if (ret < 0)
return 0;

switch (type) {
case 1:
case 5:
get_ue_golomb_long(&gb);
if (get_ue_golomb_long(&gb) > 9U)
return 0;
pps_id = get_ue_golomb_long(&gb);
if (pps_id > MAX_PPS_COUNT)
return 0;
if (!pps_ids[pps_id])
break;

if (type == 1)
sli++;
else
idr++;
break;
case 7:
skip_bits(&gb, 14);
if (get_bits(&gb, 2))
return 0;
skip_bits(&gb, 8);
sps_id = get_ue_golomb_long(&gb);
if (sps_id > MAX_SPS_COUNT)
return 0;
sps_ids[sps_id] = 1;
sps++;
break;
case 8:
pps_id = get_ue_golomb_long(&gb);
if (pps_id > MAX_PPS_COUNT)
return 0;
sps_id = get_ue_golomb_long(&gb);
if (sps_id > MAX_SPS_COUNT)
return 0;
if (!sps_ids[sps_id])
break;
pps_ids[pps_id] = 1;
pps++;
break;
}
}
}
ff_tlog(NULL, "sps:%d pps:%d idr:%d sli:%d res:%d\n", sps, pps, idr, sli, res);