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Remove RTX codec if no primary #3199

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Merged
merged 1 commit into from
Aug 22, 2025
Merged

Remove RTX codec if no primary #3199

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33 changes: 33 additions & 0 deletions rtpcodec.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ package webrtc

import (
"fmt"
"strconv"
"strings"

"github.com/pion/webrtc/v4/internal/fmtp"
Expand Down Expand Up @@ -155,6 +156,38 @@ func findRTXPayloadType(needle PayloadType, haystack []RTPCodecParameters) Paylo
return PayloadType(0)
}

// Given needle CodecParameters, returns if needle is RTX and
// if primary codec corresponding to that needle is in the haystack of codecs.
func primaryPayloadTypeForRTXExists(needle RTPCodecParameters, haystack []RTPCodecParameters) (
isRTX bool, primaryExists bool,
) {
if !strings.EqualFold(needle.MimeType, MimeTypeRTX) {
return
}

isRTX = true
parsed := fmtp.Parse(needle.MimeType, needle.ClockRate, needle.Channels, needle.SDPFmtpLine)
aptPayload, ok := parsed.Parameter("apt")
if !ok {
return
}

primaryPayloadType, err := strconv.Atoi(aptPayload)
if err != nil || primaryPayloadType < 0 || primaryPayloadType > 255 {
return
}

for _, c := range haystack {
if c.PayloadType == PayloadType(primaryPayloadType) {
primaryExists = true

return
}
}

return
}

// For now, only FlexFEC is supported.
func findFECPayloadType(haystack []RTPCodecParameters) PayloadType {
for _, c := range haystack {
Expand Down
193 changes: 193 additions & 0 deletions rtpcodec_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,199 @@ import (
"github.com/stretchr/testify/assert"
)

func TestFindPrimaryPayloadTypeForRTX(t *testing.T) {
for _, test := range []struct {
Name string
Needle RTPCodecParameters
Haystack []RTPCodecParameters
ResultIsRTX bool
ResultPrimaryExists bool
}{
{
Name: "not RTX",
Needle: RTPCodecParameters{
PayloadType: 2,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeH264,
ClockRate: 90000,
SDPFmtpLine: "apt=2",
},
},
Haystack: []RTPCodecParameters{
{
PayloadType: 1,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeH264,
ClockRate: 90000,
},
},
},
ResultIsRTX: false,
ResultPrimaryExists: false,
},
{
Name: "incorrect fmtp",
Needle: RTPCodecParameters{
PayloadType: 2,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeRTX,
ClockRate: 90000,
SDPFmtpLine: "incorrect-fmtp",
},
},
Haystack: []RTPCodecParameters{
{
PayloadType: 1,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeH264,
ClockRate: 90000,
},
},
},
ResultIsRTX: true,
ResultPrimaryExists: false,
},
{
Name: "incomplete fmtp",
Needle: RTPCodecParameters{
PayloadType: 2,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeRTX,
ClockRate: 90000,
SDPFmtpLine: "apt=",
},
},
Haystack: []RTPCodecParameters{
{
PayloadType: 1,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeH264,
ClockRate: 90000,
},
},
},
ResultIsRTX: true,
ResultPrimaryExists: false,
},
{
Name: "primary payload type outside range (negative)",
Needle: RTPCodecParameters{
PayloadType: 2,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeRTX,
ClockRate: 90000,
SDPFmtpLine: "apt=-10",
},
},
Haystack: []RTPCodecParameters{
{
PayloadType: 1,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeH264,
ClockRate: 90000,
},
},
},
ResultIsRTX: true,
ResultPrimaryExists: false,
},
{
Name: "primary payload type outside range (high positive)",
Needle: RTPCodecParameters{
PayloadType: 2,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeRTX,
ClockRate: 90000,
SDPFmtpLine: "apt=1000",
},
},
Haystack: []RTPCodecParameters{
{
PayloadType: 1,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeH264,
ClockRate: 90000,
},
},
},
ResultIsRTX: true,
ResultPrimaryExists: false,
},
{
Name: "non-matching needle",
Needle: RTPCodecParameters{
PayloadType: 2,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeRTX,
ClockRate: 90000,
SDPFmtpLine: "apt=23",
},
},
Haystack: []RTPCodecParameters{
{
PayloadType: 1,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeH264,
ClockRate: 90000,
},
},
},
ResultIsRTX: true,
ResultPrimaryExists: false,
},
{
Name: "matching needle",
Needle: RTPCodecParameters{
PayloadType: 2,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeRTX,
ClockRate: 90000,
SDPFmtpLine: "apt=1",
},
},
Haystack: []RTPCodecParameters{
{
PayloadType: 1,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeH264,
ClockRate: 90000,
},
},
},
ResultIsRTX: true,
ResultPrimaryExists: true,
},
{
Name: "matching fmtp is a substring",
Needle: RTPCodecParameters{
PayloadType: 2,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeRTX,
ClockRate: 90000,
SDPFmtpLine: "apt=1;rtx-time:2000",
},
},
Haystack: []RTPCodecParameters{
{
PayloadType: 1,
RTPCodecCapability: RTPCodecCapability{
MimeType: MimeTypeH264,
ClockRate: 90000,
},
},
},
ResultIsRTX: true,
ResultPrimaryExists: true,
},
} {
t.Run(test.Name, func(t *testing.T) {
isRTX, primaryExists := primaryPayloadTypeForRTXExists(test.Needle, test.Haystack)
assert.Equal(t, test.ResultIsRTX, isRTX)
assert.Equal(t, test.ResultPrimaryExists, primaryExists)
})
}
}

func TestFindFECPayloadType(t *testing.T) {
for _, test := range []struct {
Haystack []RTPCodecParameters
Expand Down
14 changes: 14 additions & 0 deletions rtptransceiver.go
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ package webrtc

import (
"fmt"
"strings"
"sync"
"sync/atomic"

Expand Down Expand Up @@ -60,6 +61,19 @@ func (t *RTPTransceiver) SetCodecPreferences(codecs []RTPCodecParameters) error
}
}

// remove RTX codecs if there is no corresponding primary codec
for i := len(codecs) - 1; i >= 0; i-- {
c := codecs[i]
if !strings.EqualFold(c.MimeType, MimeTypeRTX) {
continue
}

if isRTX, primaryExists := primaryPayloadTypeForRTXExists(c, codecs); isRTX && !primaryExists {
// no primary for RTX, remove the RTX
codecs = append(codecs[:i], codecs[i+1:]...)
}
}

t.codecs = codecs

return nil
Expand Down
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