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

[Baptiste Coudurier]

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.

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 ?

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
Key fingerprint                 8D77134D20CC9220201FC5DB0AC9325C5C1ABAAA
FFmpeg maintainer                                  http://www.ffmpeg.org
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