AVFMT_FLAG_NOBUFFER 对解码的影响

之前看到一文章 ijkplayer秒开
在使用它的配置之后，使用软解码怎么都是报 **Resource temporarily unavailable**
使用二分注释大法复现问题之后，发面是下面这句话导致的

pFomartCtx->flags |= AVFMT_FLAG_NOBUFFER;

所以AVFMT_FLAG_NOBUFFER为什么对软解产生影响

在avformat_find_stream_info方法中，会判断AVFMT_FLAG_NOBUFFER，而是否添加到buffer中

if (!(ic->flags & AVFMT_FLAG_NOBUFFER)) {
            ret = add_to_pktbuf(&ic->internal->packet_buffer, pkt,
                                &ic->internal->packet_buffer_end, 0);
            if (ret < 0)
                goto find_stream_info_err;

}

然后找到 avcodec_receive_frame 这么一句

    if (!avctx->internal->buffer_frame->buf[0]) {
        if (!avctx->internal->buffer_pkt->size && !avctx->internal->draining)

            return AVERROR(EAGAIN);

avctx->internal->buffer_pkt->size很好理解
avctx->internal->draining是什么?
原来只是avcodec_send_frame方法中的一个标记

• pFomartCtx->flags 还能配置什么flag?

#define AVFMT_FLAG_GENPTS       0x0001 ///< Generate missing pts even if it requires parsing future frames.
#define AVFMT_FLAG_IGNIDX       0x0002 ///< Ignore index.
#define AVFMT_FLAG_NONBLOCK     0x0004 ///< Do not block when reading packets from input.
#define AVFMT_FLAG_IGNDTS       0x0008 ///< Ignore DTS on frames that contain both DTS & PTS
#define AVFMT_FLAG_NOFILLIN     0x0010 ///< Do not infer any values from other values, just return what is stored in the container
#define AVFMT_FLAG_NOPARSE      0x0020 ///< Do not use AVParsers, you also must set AVFMT_FLAG_NOFILLIN as the fillin code works on frames and no parsing -> no frames. Also seeking to frames can not work if parsing to find frame boundaries has been disabled
#define AVFMT_FLAG_NOBUFFER     0x0040 ///< Do not buffer frames when possible
#define AVFMT_FLAG_CUSTOM_IO    0x0080 ///< The caller has supplied a custom AVIOContext, don't avio_close() it.
#define AVFMT_FLAG_DISCARD_CORRUPT  0x0100 ///< Discard frames marked corrupted
#define AVFMT_FLAG_FLUSH_PACKETS    0x0200 ///< Flush the AVIOContext every packet.
/**
 * When muxing, try to avoid writing any random/volatile data to the output.
 * This includes any random IDs, real-time timestamps/dates, muxer version, etc.
 *
 * This flag is mainly intended for testing.
 */
#define AVFMT_FLAG_BITEXACT         0x0400
#define AVFMT_FLAG_MP4A_LATM    0x8000 ///< Enable RTP MP4A-LATM payload
#define AVFMT_FLAG_SORT_DTS    0x10000 ///< try to interleave outputted packets by dts (using this flag can slow demuxing down)
#define AVFMT_FLAG_PRIV_OPT    0x20000 ///< Enable use of private options by delaying codec open (this could be made default once all code is converted)
#define AVFMT_FLAG_KEEP_SIDE_DATA 0x40000 ///< Don't merge side data but keep it separate.

#define AVFMT_FLAG_FAST_SEEK   0x80000 ///< Enable fast, but inaccurate seeks for some formats