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

[Baptiste Coudurier]

Hi Michael,

Michael Niedermayer wrote:
> 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

I'm not sure to understand what you mean here.
Can you please clarify by code ?

Do you mean
if (s->raw_packet_buffer_remaining_size >= pkt->size)
    remaining_size -= pkt->size;

?

How would you change the check above ?

[...]

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