CODEWITHSUNDEEP
webrtcchromecast
Dave Xu
Dave Xu

Reputation: 147

Try to recover media stream of Chromecast, but blocked by payload type

Captured packets from Nexus 7 to Chromecast while doing screen mirroring, but failed to recover media stream from captured packets.

Checked the detailed content in packet：

10.. .... = Version: RFC 1889 Version (2)
..0. .... = Padding: False
...0 .... = Extension: False
.... 0000 = Contributing source identifiers count: 0
0... .... = Marker: False

Payload type: DynamicRTP-Type-127 (127)
Sequence number: 11150
Timestamp: 11419287
Synchronization Source identifier: 0x00000001 (1)
Payload: 818e0000000004020064fff14c802ba00021114500145001...

Another stream marked with payload type 96. In rfc 3551, it only says "dynamic" for encoding type. (https://www.rfc-editor.org/rfc/rfc3551#page-33)

Does anyone knows details of Chromecast media stream? Is it VP8? (If it is VP8, then payload type should be something like 100 or 116 according to this page: http://www.webrtc.org/testing/analyze-packets-using-wireshark)

thanks!

Upvotes: 0

Views: 279

Answers (2)

jesup
jesup

Reputation: 6982

If it's using WebRTC for this (and last I knew it was, but that may have well have changed), the info on the type of data is in the SDP which is exchanged over encrypted channels (i.e. you can't read it). Secondarily, WebRTC traffic is all encrypted with DTLS-SRTP (i.e. you can't read more than the header of the RTP packets anyways).

tl;dr: no, you can't do that.

Upvotes: 1

Ali Naddaf
Ali Naddaf

Reputation: 19084

It is proprietary and encrypted.

Upvotes: 1

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