[FFmpeg-devel] [PATCH] probe max read size

[Michael Niedermayer]

On Wed, Jun 03, 2009 at 03:29:48PM -0700, Baptiste Coudurier wrote:
> Michael Niedermayer wrote:
> > On Mon, Jun 01, 2009 at 09:50:47PM -0700, Baptiste Coudurier wrote:
> >> Michael Niedermayer wrote:
> >>> On Mon, Jun 01, 2009 at 03:37:55PM -0700, Baptiste Coudurier wrote:
> >>>> Michael Niedermayer wrote:
> >>>>> On Mon, Jun 01, 2009 at 12:36:54PM -0700, Baptiste Coudurier wrote:
> >>>>>> Michael Niedermayer wrote:
> >>>>>>> On Sun, May 31, 2009 at 02:53:34AM -0700, Baptiste Coudurier wrote:
> >>>>>>>> Hi,
> >>>>>>>>
> >>>>>>>> After some tests, it seems more reasonable to stop probing after some
> >>>>>>>> max size to avoid consuming to much memory.
> >>>>>>> Maybe we then should replace probe_packets by a size based thing,
> >>>>>>> having 2 is uglier than one if one is sufficient
> >>>>>> Sure. Problem is per stream counting is not reasonable since streams
> >>>>>> might not have many packets present this will cause much buffering.
> >>>>> but without per stream counting streams starting once the threashold is
> >>>>> reached should fail to be probed or some streams would only be returned
> >>>>> at eof ...
> >>>> I think that, in memory constrained systems, user will want to limit:
> >>>> - raw_packet_buffer size
> >>>> - probing data size (which is btw still a problem, pd->buf must be
> >>>> released at some point if codec is not probed).
> >>>>
> >>>> To achieve this, I think both sizes must be globally bounded.
> >>>>
> >>>> Maybe by s->probesize or another field, but ideally it must be user
> >>>> configurable.
> >>> Either way the value that counts the amount remaining must be in a context
> >>> not on the stack of av_read_*
> >>>
> >>> also if it is in the context it can be set by the user
> >> Yes, definitely.
> >>
> >>>>> If we want a packet limit of PL and a byte limit of BL then
> >>>>>
> >>>>> init(){
> >>>>>     counter= BL
> >>>>> }
> >>>>> ...
> >>>>> counter -= packet.size + BL/PL;
> >>>>> if(counter > 0)
> >>>>>
> >>>>> could be used, per stream, iam not sure if this is a good idea or if
> >>>>> we rather should keep 2 counter
> >>>>>
> >>>>> Geometrically, this limit check has an area of a triangle that is within the
> >>>>> limit while the normal 2 variable check uses a rectangle, i feel that a triangle
> >>>>> is supperior ;)
> >>>> Sure, is packet limit still wanted if we have global byte limit though ?
> >>> assuming you have a 1mb size limit and a stream containing gsm
> >>> it wont ever be probebed successfully because we have no gsm probe
> >>> it has 13kbit/sec which means that no packet will be returned to the
> >>> user app for ~10 minutes when then finally all the packets will be
> >>> returned for these 10min
> >>>
> >> Patch attached. I believe using probesize is a good opportunity and I
> >> plan to replace MAX_READ_SIZE by probesize too, changing probesize
> >> default to 5000000.
> >>
> >> I find the FFMAX a bit ugly but I feel it would be safer.
> > [...]
> >> @@ -532,8 +534,13 @@ int av_read_packet(AVFormatContext *s, AVPacket *p
> >>          if (pktl) {
> >>              *pkt = pktl->pkt;
> >>              if(s->streams[pkt->stream_index]->codec->codec_id != CODEC_ID_PROBE ||
> >> -               !s->streams[pkt->stream_index]->probe_packets){
> >> +               !s->streams[pkt->stream_index]->probe_packets ||
> >> +               s->raw_packet_buffer_remaining_size <= 0){
> >> +                AVProbeData *pd = &st->probe_data;
> >> +                av_freep(&pd->buf);
> >> +                pd->buf_size = 0;
> >>                  s->raw_packet_buffer = pktl->next;
> >> +                s->raw_packet_buffer_remaining_size += pkt->size;
> >>                  av_free(pktl);
> >>                  return 0;
> >>              }
> > 
> >> @@ -567,6 +574,8 @@ int av_read_packet(AVFormatContext *s, AVPacket *p
> >>              return ret;
> >>  
> >>          add_to_pktbuf(&s->raw_packet_buffer, pkt, &s->raw_packet_buffer_end);
> >> +        s->raw_packet_buffer_remaining_size =
> >> +            FFMAX(0, s->raw_packet_buffer_remaining_size - pkt->size);
> >>  
> >>          if(st->codec->codec_id == CODEC_ID_PROBE){
> >>              AVProbeData *pd = &st->probe_data;
> > 
> > is the combination of FFMAX here and the += pkt->size; above not able to
> > change raw_packet_buffer_remaining_size to a value that is beyond the
> > initial limit ?
> 
> That's possible indeed, I was wondering is this would be safe. If you
> think it's safer to limit it as well, here is an updated patch.

i think it should be possible to remove both FFMIN&MAX
we just have to check the remaining size against the packet size instead
of against 0 then we can always saftely subtract it


> 
> Also, what do you about using s->probesize instead of MAX_READ_SIZE in
> av_find_stream_info and raising the default up to MAX_READ_SIZE or
> another value ?

iam fine with these i think

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

While the State exists there can be no freedom; when there is freedom there
will be no State. -- Vladimir Lenin
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