[FFmpeg-devel] MPEG-PS demuxer index memory usage

[Michael Niedermayer]

On Thu, Jan 03, 2008 at 10:48:49PM +0000, Paul Kelly wrote:
> Hello
> I'm using libavformat to demux a continuous stream of MPEG2-PS data and am 
> running into the problem that memory usage steadily increases over time. 
> The problem is not observed when demuxing an MPEG2-TS stream.
> 
> After a bit of digging around I discovered the problem is caused by the 
> timestamp indexing in the PS demuxer - specifically, the calls to 
> av_add_index_entry() in mpegps_read_pes_header() in libavformat/mpeg.c. 
> All I'm doing is transcoding the stream to a different output format and I 
> don't need to be able to perform seeking but there doesn't seem to be any 
> way to disable the index. (I guess the memory occupied by the index isn't 
> a problem if a fixed-size file is being demuxed, but in my case I am 
> reading data from a hardware MPEG encoder card and splitting the output 
> into separate files and the process is required to run indefinitely - the 
> index quickly grows to an unwieldy size.)
> 
> As far as I can see the flag AVFMT_GENERIC_INDEX can be turned off to stop 
> indexing if generic indexing is used (perhaps that's a non-standard usage 
> though) - but is there no way to turn off the indexing in the MPEG-PS 
> demuxer?
> 
> Might it be a good idea to add another flag to turn off the 
> demuxer-specific indexing, and make individual demuxers respect this? A 
> general catch-all way of disabling indexing (or specifying that seeking 
> isn't required) might be more elegant though.
> 
> I can get over the immediate problem by simply commenting out the line 
> calling av_add_index_entry() in libavformat/mpeg.c, but would like to help 
> get a better solution into libavformat if I can.

Disabling it with a flag is surely interresting. But i think there are better
solutions.
One for example would be a max_index_size. And when thats reached index
entries would be pseudo randomly droped. That would limit the used memory and
still speed up seeking.

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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