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使用说明
当前为了避免在调用init_input函数的时候，读取缓存区的数据，从而设置了该标志位,但是最终在avformat_open_input的其他地方还是读取了缓冲区的数据
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pAVInputFormat = av_find_input_format("h364");
pAVInputFormat->flags |= AVFMT_NOFILE;
宏定义
/// Demuxer will use avio_open, no opened file should be provided by the caller.
//解复用器将调用avio_open函数，调用者提供一个没有打开的文件，估计是打开的文件会被占用
#define AVFMT_NOFILE 0x0001
#define AVFMT_NEEDNUMBER 0x0002 /**< Needs '%d' in filename. */
#define AVFMT_SHOW_IDS 0x0008 /**< Show format stream IDs numbers. */
AVFMT_NOFILE formats will not have a AVIOContext
当设置了AVFMT_NOFILE标志，将不会携带AVIOContext
/* Open input file and probe the format if necessary. */
static int init_input(AVFormatContext *s, const char *filename,
AVDictionary **options)
{
int ret;
AVProbeData pd = { filename, NULL, 0 };
int score = AVPROBE_SCORE_RETRY;
//这里探测码流的方式，企图通过AVIOContext结构体中的read_packet函数
//如果码流格式已经指定并且指定了标志位，直接返回
if (s->pb) {
s->flags |= AVFMT_FLAG_CUSTOM_IO;
//如果没有指定输入格式，开始探测码流格式
if (!s->iformat)
return av_probe_input_buffer2(s->pb, &s->iformat, filename,
s, 0, s->format_probesize);
else if (s->iformat->flags & AVFMT_NOFILE)
av_log(s, AV_LOG_WARNING, "Custom AVIOContext makes no sense and "
"will be ignored with AVFMT_NOFILE format.\n");
return 0;
}
//这里探测码流的方式，企图通过通过进来的文件名称
//如果码流格式已经指定并且指定了标志位，直接返回
//这里非常明显网络RTSP流，肯定是不会走到这里
if ((s->iformat && s->iformat->flags & AVFMT_NOFILE) ||
(!s->iformat && (s->iformat = av_probe_input_format2(&pd, 0, &score))))
return score;
//如果指定了iformat结构体，并且没有设置标志位，肯定执行下面的语句，该语句会调用read_packet函数
//进行分析码流
if ((ret = s->io_open(s, &s->pb, filename, AVIO_FLAG_READ | s->avio_flags, options)) < 0)
return ret;
if (s->iformat)
return 0;
return av_probe_input_buffer2(s->pb, &s->iformat, filename,
s, 0, s->format_probesize);
}
从下面的说明可以得知，当添加了AVFMT_NOFILE标志位，AVIOContext *pb会设置为空
/**
* I/O context.
*
* - demuxing: either set by the user before avformat_open_input() (then
* the user must close it manually) or set by avformat_open_input().
* - muxing: set by the user before avformat_write_header(). The caller must
* take care of closing / freeing the IO context.
*
* Do NOT set this field if AVFMT_NOFILE flag is set in
* iformat/oformat.flags. In such a case, the (de)muxer will handle
* I/O in some other way and this field will be NULL.
*/
AVIOContext *pb;
/**
* Custom interrupt callbacks for the I/O layer.
*
* demuxing: set by the user before avformat_open_input().
* muxing: set by the user before avformat_write_header()
* (mainly useful for AVFMT_NOFILE formats). The callback
* should also be passed to avio_open2() if it's used to
* open the file.
*/
AVIOInterruptCB interrupt_callback;
/**
* Guess the file format.
*
* @param pd data to be probed
* @param is_opened Whether the file is already opened; determines whether
* demuxers with or without AVFMT_NOFILE are probed.
*/
AVInputFormat *av_probe_input_format(AVProbeData *pd, int is_opened);
AVInputFormat *av_probe_input_format2(AVProbeData *pd, int is_opened, int *score_max);
AVInputFormat *av_probe_input_format3(AVProbeData *pd, int is_opened, int *score_ret);