[FFmpeg-devel] [PATCH] libavformat/rtsp: fix rtsp multicasts

[Wolfgang Haupt]

On 19.04.20 23:43, Marton Balint wrote:
>
>
> On Sun, 19 Apr 2020, Wolfgang Haupt wrote:
>
>> On 19.04.20 14:53, Marton Balint wrote:
>>>
>>>
>>> On Sun, 19 Apr 2020, Wolfgang Haupt wrote:
>>>
>>>> ping
>>>>
>>>> On 03.04.20 08:42, Wolfgang Haupt wrote:
>>>>> Hey,
>>>>>
>>>>> is someone up to review this patch?
>>>>>
>>>>> It's an attempt to fix rtsp streams that use udp multicasts as the 
>>>>> underlying
>>>>> transmission protocol.
>>>>> The idea was taken from live555 as the said stream worked in VLC.
>>>>>
>>>>> It still applies cleanly on current master.
>>>>>
>>>>>
>>>>> Best Regards,
>>>>> Wolfgang
>>>>>
>>>>> On 18.10.19 18:59, Wolfgang Haupt wrote:
>>>>>> If an rtsp server offers a udp multicast
>>>>>> address as response of a DESCRIBE command
>>>>>> the rtsp client is expected to issue
>>>>>> SETUP with "Transport: RTP/AVP/UDP;multicast".
>>>>>> Some rtsp servers bail out otherwise.
>>>>>> ---
>>>>>>   libavformat/rtsp.c | 3 +++
>>>>>>   1 file changed, 3 insertions(+)
>>>>>>
>>>>>> diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c
>>>>>> index 859defa592..3f0cbfc98b 100644
>>>>>> --- a/libavformat/rtsp.c
>>>>>> +++ b/libavformat/rtsp.c
>>>>>> @@ -1913,6 +1913,9 @@ redirect:
>>>>>>                   && (rt->rtsp_flags & RTSP_FLAG_PREFER_TCP))
>>>>>>               lower_transport = RTSP_LOWER_TRANSPORT_TCP;
>>>>>>   +        if (ff_is_multicast_address((struct 
>>>>>> sockaddr*)&rt->rtsp_streams[rt->nb_rtsp_streams-1]->sdp_ip))
>>>>>> +            lower_transport = RTSP_LOWER_TRANSPORT_UDP_MULTICAST;
>>>>>> +
>>>
>>> Shouldn't this take into account lower_transport_mask? E.g. it 
>>> should only prefer multicast if it is allowed in the mask?
>>
>> Can you explain what the lower_transport_mask is about?
>> I cannot think of any case where you wouldn't want use udp multicast 
>> when the rtsp server gives you a mutlicast-ip
>> in response to a DESCRIBE request.
>
> I am not familiar with the code, but it looks like it is used to 
> control the allowed (tried) transport methods. The rtsp protocol has 
> an rtsp_transport option, that is the source of the mask:
> https://www.ffmpeg.org/ffmpeg-all.html#rtsp
> If UDP multicast transport is disallowed because it is not in the mask 
> then you should not set it as far as I see.

Mhm, yeah that's actually the problem I tried to fix.
Reading the docs again, I'm not sure if I missed it before, but the docs 
are stating:
Multiple lower transport protocols may be specified, in that case they 
are tried one at a time (if the setup of one fails, the next one is 
tried). For the muxer, only the ‘tcp’ and ‘udp’ options are supported.

However I still cannot manage to get udp + udp_multicast into the 
lower_transport_mask on the commandline, so I'm still not sure how/if 
it's possible to really set multiple protocols.
Therefore my patch always adds "udp_multicast" as lower_transport no 
matter what the lower_transport_mask is as soon as the DESCRIBE response 
returns a multicast IP, because
clients don't know when to set udp vs. udp_multicast as you can't know 
which stream you get.

>
> Regards,
> Marton
>
>>
>>>
>>> Thanks,
>>> Marton
>>>
>>>>>>           err = ff_rtsp_make_setup_request(s, host, port, 
>>>>>> lower_transport,
>>>>>>                                    rt->server_type == 
>>>>>> RTSP_SERVER_REAL ?
>>>>>>                                        real_challenge : NULL);
>>>>>
>>>>>
>>>>
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