标签:mod @param todo 获取 code getting packet ext 头部
/** * Read packets of a media file to get stream information. This * is useful for file formats with no headers such as MPEG. This * function also computes the real framerate in case of MPEG-2 repeat * frame mode. * The logical file position is not changed by this function; * examined packets may be buffered for later processing. * * @param ic media file handle * @param options If non-NULL, an ic.nb_streams long array of pointers to * dictionaries, where i-th member contains options for * codec corresponding to i-th stream. * On return each dictionary will be filled with options that were not found. * @return >=0 if OK, AVERROR_xxx on error * * @note this function isn‘t guaranteed to open all the codecs, so * options being non-empty at return is a perfectly normal behavior. * * @todo Let the user decide somehow what information is needed so that * we do not waste time getting stuff the user does not need. */ int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options);
该函数主要用于获取视频流信息。
在一些格式当中没有头部信息,如flv格式,h264格式,这个时候调用avformat_open_input()在打开文件之后就没有参数,也就无法获取到里面的信息。这个时候就可以调用此函数,因为它会试着去探测文件的格式,但是如果格式当中没有头部信息,那么它只能获取到编码、宽高这些信息,还是无法获得总时长。如果总时长无法获取到,则仍需要把整个文件读一遍,计算一下它的总帧数。
例:
if (avformat_find_stream_info(ic, 0) >=0 ) { LOGI("duration is: %lld, nb_stream is: %d", ic->duration, ic->nb_streams); }
其中的ic就是 AVFormatContext 的指针。
FFmpeg(4)-使用avformat_find_stream_info()来探测获取封装格式的上下文信息
标签:mod @param todo 获取 code getting packet ext 头部
原文地址:https://www.cnblogs.com/yongdaimi/p/9797128.html