id	summary	reporter	owner	description	type	status	priority	component	version	resolution	keywords	cc	blockedby	blocking	reproduced	analyzed
1607	av_seek_frame() without AVSEEK_FLAG_ANY on mpg files returns success without seeking to a keyframe	mbradshaw		"The documentation of `av_seek_frame()` makes a contract that it seeks to a keyframe if `AVSEEK_FLAG_ANY` is not set. mpg files break this contract by not seeking to a keyframe and still returning success.

'''Updated Edit:'''
It seems that any `AVInputFormat` that doesn't have it's own `read_seek()` or `read_seek2()` functions defined will default to either `ff_seek_frame_binary()` or `ff_gen_search()` (with priority given to `ff_seek_frame_binary()`). `ff_seek_frame_binary()` doesn't respect seeking by keyframe, and will break the keyframe contract made by `av_seek_frame()` when `AVSEEK_FLAG_ANY` is not set.

Proposed solutions:
'''1)'''
Seeking in mpg should require `AVSEEK_FLAG_ANY` to be set in order for success to be returned (return failure if it's not specified). This can be done by requiring `AVSEEK_FLAG_ANY` to be set before calling `ff_seek_frame_binary()`.

'''2) (in response to Don's suggestions)'''
Change `ff_seek_frame_binary()` so that it respects seeking by keyframe if `AVSEEK_FLAG_ANY` is not set. This can be done by sequentially reading (either forwards or backwards (I would prefer backwards)) up to a keyframe after the binary search is complete.

For context on how this came about, see this thread: http://ffmpeg.org/pipermail/libav-user/2012-July/002468.html

I originally opened ticket #1575 but Don Moir pointed out this is more of a bug than a lack of documentation."	defect	new	normal	avformat	git-master			donmoir@…			0	0