refer to this if u wanna understand what really keyframe is
http://en.wikipedia.org/wiki/Video_compression_picture_types
also do remember it was also quiet confusing for me av_seek_frame seek
stream by DTS (Decode Time Stamp) and not by PTS (Presentation Time
Stamp) so when you seek you are'nt going get to the accurate position of
the stream
On 12/09/2013 09:29 AM, YIRAN LI wrote:
And I have another question: If an AVPacket object has AV_PKT_FLAG_KEY
bit set in flags, does that mean this packet when passed into
avcodec_decode_video2 can always get a complete frame (I mean by
calling avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished,
&packet) the 3rd argument set to true)?
Thanks
2013/12/9 YIRAN LI <[email protected] <mailto:[email protected]>>
Thanks Don,
So in order to get a correct image, I must not use AVSEEK_FLAG_ANY
so that av_seek_frame by default will seek to a key frame. And I
should continue to read from that point and decode until I get a
frame with the timestamp I want.
Do you know if all demuxers can support av_seek_frame() correctly
so that as long as there's a key frame before the position I pass
to the function, they all can correctly seek to that key frame?
Thanks
2013/12/4 Don Moir <[email protected] <mailto:[email protected]>>
>----- Original Message -----
>From: YIRAN LI
>To: This list is about using libavcodec, libavformat,
libavutil,libavdevice and libavfilter.
>Sent: Sunday, December 08, 2013 9:44 PM
>Subject: [Libav-user] a question for av_seek_frame
>Hi friends
>Here I have a question about av_seek_frame.
>For example if I have a video stream of time stamps 0, 1, 2,
3, 4, 5, 6, 7, 8, 9, 10. and only frame at 0 is a key frame.
>if I call av_seek_frame(x,x,5, AVSEEK_FLAG_BACKWARD |
AVSEEK_FLAG_ANY) and then av_read_frame, the first frame I get
will be frame 6, is this correct?
>then if I call av_seek_frame(x, x, 5, AVSEEK_FLAG_BACKWARD)
and then av_read_frame, then the first frame I get will be
frame 1, is this correct?
>and if both can seek to a frame and first one can get a frame
quicker, in what circumstance should I use the second one?
>Thanks
Non key frames require the previous key frame in order to be
decoded correctly. So if you skip past the key frame to frame
6, then the decoded image will most likely be incorrect.
While your first example may be quicker, it will not be
correct. Best to stay away from AVSEEK_FLAG_ANY for normal
display purposes. Proper seeking to frame 6 would require a
seek to frame 1 and then read and decode to frame 6.
AVSEEK_FLAG_ANY can be useful in some cases but generally not
for normal display.
_______________________________________________
Libav-user mailing list
[email protected] <mailto:[email protected]>
http://ffmpeg.org/mailman/listinfo/libav-user
_______________________________________________
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
