【FFmpeg】av_guess_frame_rate

• 流的帧率

基于容器和编码信息

• 猜测的是AVFrame的。
• 可以传递null

/*** Guess the frame rate, based on both the container and codec information.** @param ctx the format context which the stream is part of* @param stream the stream which the frame is part of* @param frame the frame for which the frame rate should be determined, may be NULL* @return the guessed (valid) frame rate, 0/1 if no idea*/
AVRational av_guess_frame_rate(AVFormatContext *ctx, AVStream *stream, AVFrame *frame);