I have various videos that are VBR and don't have an accurate duration
or frame rate.
I wrote some code to index the files by reading through the whole thing
by packet and recording the pts, byte offset, and duration for each
frame, and recording which ones are I-frames. This also allows getting
an accurate duration for the files that didn't have one too.
Now I'm attempting to use the index to jump to any arbitrary frame, by
first seeking to the byte offset of the I-frame before the desired
frame, and then decoding packets until the desired number of
non-I-frames are processed.
I've tried this both using the byte offset and with the pts of that
reference I-frame, but in many cases I'm getting repeating "loops" in
the video.
This is probably my misunderstanding of what the fields in the AVFrame
are. While building the index, I'm using a loop of av_read_frame() and
avcodec_decode_video2(). When I get a picture, and if key_frame is set,
I record the frame's pkt_pos, pts, and pkt_dts values in a dictionary
keyed by the frame number.
When I seek to an arbitrary frame, I look up the first entry in the
dictionary with the frame # I'm looking for, and then to:
av_seek_frame(context, video_stream_index, pkt_pos_for_nearest_iframe,
AVSEEK_FLAG_BACKWARD | AVSEEK_FLAG_BYTES);
Then if the frame I'm looking for is not an I-frame, I repeat the
av_frame_read/avcodec_decode_video2 loop until I get to that frame number.
Does anyone have any experience with this kind of thing who could tell
me what I'm doing wrong?
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