[MPlayer-dev-eng] NUT (informal) proposal, based on discussions

[Oded Shimon]

On Fri, Jan 20, 2006 at 03:13:15PM +0100, Michael Niedermayer wrote:
> Hi
> 
> On Fri, Jan 20, 2006 at 02:59:25PM +0100, Michael Niedermayer wrote:
> [...]
> > [...]
> > > BTW, does anyone have a good idea for efficient but simple data structure 
> > > for decoded index?... The naive way requires 
> > > streams*syncpoints*sizeof(uint64_t) memory, which is too much. (5mb of 
> > > ram?..) Any other idea I can think of requires some complication for 
> > > just using the values or changing them... (I still want the ability to 
> > > dynamically build the index while playing)
> > 
> > 5mb? i came up with 10mb for a 4gb 10stream file, and for thouse now shouting
> > 10mb isnt an issue for 4gb files, it is a big issue as thats RAM and a DVD
> > player shouldnt need 10mb RAM for the index
> > ahh, one solution, drop the PTS and the index will need <200kb in RAM
> > and yes every demuxer will do this IMHO, it doesnt even break optimal
> > seeking:
> > exact seeking: find the prevous syncpoint P for timestamp X then find the
> > earliest syncpoint which has a keyframe prior P in every wanted stream
> > optimal seeking: do the same but additionally check if syncpoint P itself
> > already contains a keyframe for every stream we want (0 seeks) and if so
> > check if they are before X (1 extra seek)
> > now let the flamewars begin again about why 10mb memory, 64x larger RAM 
> > and 10x larger index in the file is worth saving 1 _rarely_needed_ seek
> > for optimal seeking
> 
> after thinking about it a little the RAM argument obviously is silly
> just have an array of indexes/pointers (4*syncpoints bytes) and let
> these point into a array which has stream_id+pts entries its not as
> simply as a simple flat array but it needs just 4*syncpoints + 10*keyframes
> bytes, instead of 8*streams*syncpoints

I already did something similar and crazier:

struct syncpoint_list {
	off_t * pos;
	uint64_t * pts;
	int len;
} s;
uint64_t * p = s->pts;

for (i = 0; i < sl->len; i++) {
	int n = s->pos[i] % (nut->stream_count + 1);
	for (j = 0; j < n; j++) {
		stream = p[j] % nut->stream_count;
		pts = p[j] / nut->stream_count;
		...
	}
	p += n;
}


But I evantually decided it is not worth it. BTW, without the pts, decoded 
index is still nowhere near <200kb, it is atleast 1mb to store just off_t 
of syncpoint positions.

> a player chould also choose to simplify the PTS based on the set of active
> streams during index loading

In libnut API active_streams is defined at nut_seek, not init.

- ods15