Adds WithPacketHeadHandler to SampleBuilder

[digitalix]

Description

This option allows inspecting head packet for each media.Sample and then lets the user return their custom metadata. This might be useful in case when you need to check whether the given sample is a keyframe.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.05% ⚠️

Comparison is base (b40f599) 77.60% compared to head (37d9288) 77.56%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1967      +/-   ##
==========================================
- Coverage   77.60%   77.56%   -0.05%     
==========================================
  Files          87       87              
  Lines        9365     9374       +9     
==========================================
+ Hits         7268     7271       +3     
- Misses       1667     1672       +5     
- Partials      430      431       +1     

Flag	Coverage Δ
go	79.32% <100.00%> (-0.05%)	⬇️
wasm	70.23% <100.00%> (+0.07%)	⬆️

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Files Changed	Coverage Δ
pkg/media/samplebuilder/samplebuilder.go	95.71% <100.00%> (+0.19%)	⬆️

... and 3 files with indirect coverage changes

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[Sean-Der]

Hey @digitalix Sorry this took so long.

I see how this is useful! You are interested in the RTP Payload Header, but are just getting samples.

interface{} in+out feels wrong to me. What if we could find a way to expose Unmarshaled packet headers (but not payloads?) Like VP9Packet

@jech you have opinions on the SampleBuilder. What do you think of the problem?

[digitalix]

Hey @digitalix Sorry this took so long.

I see how this is useful! You are interested in the RTP Payload Header, but are just getting samples.

interface{} in+out feels wrong to me. What if we could find a way to expose Unmarshaled packet headers (but not payloads?) Like VP9Packet

@jech you have opinions on the SampleBuilder. What do you think of the problem?

You're right @Sean-Der with interface{} as in+out. Hmm... As in we could use rtp.Depacketizer but I'd prefer to create an alias for it e.g.MediaPacket.

For out we could split VP9Packet (and others) into VP9Packet and VP9PacketHeader that would be embedded within VP9Packet.

[jech]

I think it's pretty smart.

[Sean-Der]

Merging!

Sorry this took so long @digitalix. The usage of interface{} I think totally makes sense here.

Users are supplying this data anyway. I think it would be worse for us to force a shape.