[FFmpeg-devel] MPEG-PS demuxer index memory usage
Fri Jan 4 04:16:38 CET 2008
On Thu, Jan 03, 2008 at 10:48:49PM +0000, Paul Kelly wrote:
> 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
> 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
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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