[FFmpeg-devel] MPEG-PS demuxer index memory usage
Fri Jan 4 17:50:01 CET 2008
Michael Niedermayer a ?crit :
> 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.
Another possibility (not exclusive):
After all, if the input is streamed, the index is unlikely to be of any use!
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