How do I use “Stream Analysis” on RTP packets with payload type 0x14 (d'20)

The payload type is custom (using PT=20) and defined as:

PayloadType payload_type_pcm8000 =
TYPE( PAYLOAD_AUDIO_CONTINUOUS),
CLOCK_RATE(8000),
BITS_PER_SAMPLE(16),
ZERO_PATTERN( offset0),
PATTERN_LENGTH(1),
NORMAL_BITRATE( 128000),
MIME_TYPE ("PCM"),
CHANNELS(1)

I cannot play the audio directly in Wireshark and neither get any analysis of the data in regards of jitter for example. I can save the stream as .raw data from Wireshark and then import this file in AudaCity (for example) as signed 16 bit PCM at 8000 samples / second. And here I can listen to the audio file. However this does not reflect the delay on the network and results in a perfect sound listening on the receiver side I have a "fuzzy" sound.

To be able to analyze this behavior I was hopping to analyze the network traffic to tell if the sound is distorted on the transmitter or receiver side. Can I tell Wireshark what I'm expecting in the payload for this data type or is there any other good way on how I can analyze RTP data.

The test setup is:

| Transmitter | ---> | Mirroring switch | ---> | Receiver |
                               ↓
                  | Computer with Wireshark |

I have access to the source code on the receiver and can change this if I needed, but I cannot control the transmitter side (at least not directly). The return audio is clear and good (using the same protocol and network interface).

edit: Wireshark version: Version 2.2.3 (v2.2.3-0-g57531cd)