> Le 9 déc. 2014 à 11:00, Vadim Fedorov <[email protected]> a écrit : > > Hi, > > Not really, because your 100th frame depends on the 99th frame (or maybe on > 98th), but not directly on the 1st one. However, indirectly it is still > depends on the key frame, because 99th depends on 98th and so on. This means > that to get your 100th frame you should start from the key frame and decode > all 98 frames in between. > > Best regards, > Vadim > > 2014-12-09 10:30 GMT+01:00 YIRAN LI <[email protected]>: >>> >>>> Le 9 déc. 2014 à 08:12, YIRAN LI <[email protected]> a écrit : >>>> >>>> Hi, >>>> >>>> I have a question about read frame, >>>> >>>> Suppose I've just opened a file, so the readpointer is at the beginning of >>>> the file. >>>> >>>> Compare these two methods: >>>> >>>> 1. call av_read_frame + avcode_decode_video2 to decode 100 video packets( >>>> suppose each packet can decode into a frame) >>>> 2. call av_read_frame, but only decode the 100th packet (all previous 99 >>>> packets are just discarded) >>>> >>>> Will the 100th frame from method 1 and the frame from method 2 have same >>>> content, timestamp, etc? >>>> >>>> Thanks >>> >>> Hi, >>> >>> Decoding the 100th packet alone can be equivalent in both situations only >>> if this packet is a keyframe. If not, FFmpeg will need all the packets up >>> to the first preceding key frame in order to be able to give you a frame >>> with correct content. I'm unsure whether other metadata like timestamp >>> depend on the method (although I don't think so). >> >> Thanks Lucas, >> >> Let's assume both 2 methods start reading from a key packet. and the next >> key is in the 200th packet. >> >> So you mean continuously decoding to 100th frame has same result as skip 99 >> and decode 100th alone?
Not sure I got the situation. As soon as you start skipping packets, you are not guaranteed to have correct content until you reach the next key frame. >> >> >>> Lucas >>> >>> _______________________________________________ >>> Libav-user mailing list >>> [email protected] >>> http://ffmpeg.org/mailman/listinfo/libav-user >> >> >> _______________________________________________ >> Libav-user mailing list >> [email protected] >> http://ffmpeg.org/mailman/listinfo/libav-user > > > > -- > С уважением, > Вадим Фёдоров > _______________________________________________ > Libav-user mailing list > [email protected] > http://ffmpeg.org/mailman/listinfo/libav-user
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