1）h264_probe函數剖析
函數調用
avformat_open_input
s->iformat->read_header(s)
函數說明
/**
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 *);
從read_header函數調用，去探測h264的碼流格式
代碼說明
static int h264_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];
//分離出NAL起始碼00 00 00 01 分析出NAL類型
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)
if (ref_zero[type] == -1 && !ref_idc)
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)
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)
if (!pps_ids[pps_id])
break;
if (type == 1)
sli++;
else
idr++;
break;
case 7:
skip_bits(&gb, 14);
if (get_bits(&gb, 2))
skip_bits(&gb, 8);
sps_id = get_ue_golomb_long(&gb);
if (sps_id > MAX_SPS_COUNT)
sps_ids[sps_id] = 1;
sps++;
case 8:
if (!sps_ids[sps_id])
pps_ids[pps_id] = 1;
pps++;
}
}
ff_tlog(NULL, "sps:%d pps:%d idr:%d sli:%d res:%d\n", sps, pps, idr, sli, res);
if (sps && pps && (idr || sli > 3) && res < (sps + pps + idr))
return AVPROBE_SCORE_EXTENSION + 1; // 1 more than .mpg
return 0;
2）播放
VLC media player 預設不支援播放H264資料流
目前使用VLC的版本是2.2.4Weatherwax
操作步驟
1 打開菜單欄的工具
2 選擇首選項
3 在界面TAB頁面的左下角有兩個單選框，簡明，全部 旁邊有一個重置參數
4 點選全部
5 點選輸入/編×××菜單,在下拉清單中點選去複用器，但不不需要展開去複用器的下拉清單
6 在右上角的位置，去複用子產品中選擇H264 視訊去複用器