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vlaextension.go
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vlaextension.go
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// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT
package rtp
import (
"encoding/binary"
"errors"
"fmt"
"strings"
"github.com/pion/rtp/codecs/av1/obu"
)
var (
ErrVLATooShort = errors.New("VLA payload too short") // ErrVLATooShort is returned when payload is too short
ErrVLAInvalidStreamCount = errors.New("invalid RTP stream count in VLA") // ErrVLAInvalidStreamCount is returned when RTP stream count is invalid
ErrVLAInvalidStreamID = errors.New("invalid RTP stream ID in VLA") // ErrVLAInvalidStreamID is returned when RTP stream ID is invalid
ErrVLAInvalidSpatialID = errors.New("invalid spatial ID in VLA") // ErrVLAInvalidSpatialID is returned when spatial ID is invalid
ErrVLADuplicateSpatialID = errors.New("duplicate spatial ID in VLA") // ErrVLADuplicateSpatialID is returned when spatial ID is invalid
ErrVLAInvalidTemporalLayer = errors.New("invalid temporal layer in VLA") // ErrVLAInvalidTemporalLayer is returned when temporal layer is invalid
)
// SpatialLayer is a spatial layer in VLA.
type SpatialLayer struct {
RTPStreamID int
SpatialID int
TargetBitrates []int // target bitrates per temporal layer
// Following members are valid only when HasResolutionAndFramerate is true
Width int
Height int
Framerate int
}
// VLA is a Video Layer Allocation (VLA) extension.
// See https://webrtc.googlesource.com/src/+/refs/heads/main/docs/native-code/rtp-hdrext/video-layers-allocation00
type VLA struct {
RTPStreamID int // 0-origin RTP stream ID (RID) this allocation is sent on (0..3)
RTPStreamCount int // Number of RTP streams (1..4)
ActiveSpatialLayer []SpatialLayer
HasResolutionAndFramerate bool
}
type vlaMarshalingContext struct {
slMBs [4]uint8
sls [4][4]*SpatialLayer
commonSLBM uint8
encodedTargetBitrates [][]byte
requiredLen int
}
func (v VLA) preprocessForMashaling(ctx *vlaMarshalingContext) error {
for i := 0; i < len(v.ActiveSpatialLayer); i++ {
sl := v.ActiveSpatialLayer[i]
if sl.RTPStreamID < 0 || sl.RTPStreamID >= v.RTPStreamCount {
return fmt.Errorf("invalid RTP streamID %d:%w", sl.RTPStreamID, ErrVLAInvalidStreamID)
}
if sl.SpatialID < 0 || sl.SpatialID >= 4 {
return fmt.Errorf("invalid spatial ID %d: %w", sl.SpatialID, ErrVLAInvalidSpatialID)
}
if len(sl.TargetBitrates) == 0 || len(sl.TargetBitrates) > 4 {
return fmt.Errorf("invalid temporal layer count %d: %w", len(sl.TargetBitrates), ErrVLAInvalidTemporalLayer)
}
ctx.slMBs[sl.RTPStreamID] |= 1 << sl.SpatialID
if ctx.sls[sl.RTPStreamID][sl.SpatialID] != nil {
return fmt.Errorf("duplicate spatial layer: %w", ErrVLADuplicateSpatialID)
}
ctx.sls[sl.RTPStreamID][sl.SpatialID] = &sl
}
return nil
}
func (v VLA) encodeTargetBitrates(ctx *vlaMarshalingContext) {
for rtpStreamID := 0; rtpStreamID < v.RTPStreamCount; rtpStreamID++ {
for spatialID := 0; spatialID < 4; spatialID++ {
if sl := ctx.sls[rtpStreamID][spatialID]; sl != nil {
for _, kbps := range sl.TargetBitrates {
leb128 := obu.WriteToLeb128(uint(kbps))
ctx.encodedTargetBitrates = append(ctx.encodedTargetBitrates, leb128)
ctx.requiredLen += len(leb128)
}
}
}
}
}
func (v VLA) analyzeVLAForMarshaling() (*vlaMarshalingContext, error) {
// Validate RTPStreamCount
if v.RTPStreamCount <= 0 || v.RTPStreamCount > 4 {
return nil, ErrVLAInvalidStreamCount
}
// Validate RTPStreamID
if v.RTPStreamID < 0 || v.RTPStreamID >= v.RTPStreamCount {
return nil, ErrVLAInvalidStreamID
}
ctx := &vlaMarshalingContext{}
err := v.preprocessForMashaling(ctx)
if err != nil {
return nil, err
}
ctx.commonSLBM = commonSLBMValues(ctx.slMBs[:])
// RID, NS, sl_bm fields
if ctx.commonSLBM != 0 {
ctx.requiredLen = 1
} else {
ctx.requiredLen = 3
}
// #tl fields
ctx.requiredLen += (len(v.ActiveSpatialLayer)-1)/4 + 1
v.encodeTargetBitrates(ctx)
if v.HasResolutionAndFramerate {
ctx.requiredLen += len(v.ActiveSpatialLayer) * 5
}
return ctx, nil
}
// Marshal encodes VLA into a byte slice.
func (v VLA) Marshal() ([]byte, error) {
ctx, err := v.analyzeVLAForMarshaling()
if err != nil {
return nil, err
}
payload := make([]byte, ctx.requiredLen)
offset := 0
// RID, NS, sl_bm fields
payload[offset] = byte(v.RTPStreamID<<6) | byte(v.RTPStreamCount-1)<<4 | ctx.commonSLBM
if ctx.commonSLBM == 0 {
offset++
for streamID := 0; streamID < v.RTPStreamCount; streamID++ {
if streamID%2 == 0 {
payload[offset+streamID/2] |= ctx.slMBs[streamID] << 4
} else {
payload[offset+streamID/2] |= ctx.slMBs[streamID]
}
}
offset += (v.RTPStreamCount - 1) / 2
}
// #tl fields
offset++
var temporalLayerIndex int
for rtpStreamID := 0; rtpStreamID < v.RTPStreamCount; rtpStreamID++ {
for spatialID := 0; spatialID < 4; spatialID++ {
if sl := ctx.sls[rtpStreamID][spatialID]; sl != nil {
if temporalLayerIndex >= 4 {
temporalLayerIndex = 0
offset++
}
payload[offset] |= byte(len(sl.TargetBitrates)-1) << (2 * (3 - temporalLayerIndex))
temporalLayerIndex++
}
}
}
// Target bitrate fields
offset++
for _, encodedKbps := range ctx.encodedTargetBitrates {
encodedSize := len(encodedKbps)
copy(payload[offset:], encodedKbps)
offset += encodedSize
}
// Resolution & framerate fields
if v.HasResolutionAndFramerate {
for _, sl := range v.ActiveSpatialLayer {
binary.BigEndian.PutUint16(payload[offset+0:], uint16(sl.Width-1))
binary.BigEndian.PutUint16(payload[offset+2:], uint16(sl.Height-1))
payload[offset+4] = byte(sl.Framerate)
offset += 5
}
}
return payload, nil
}
func commonSLBMValues(slMBs []uint8) uint8 {
var common uint8
for i := 0; i < len(slMBs); i++ {
if slMBs[i] == 0 {
continue
}
if common == 0 {
common = slMBs[i]
continue
}
if slMBs[i] != common {
return 0
}
}
return common
}
type vlaUnmarshalingContext struct {
payload []byte
offset int
slBMField uint8
slBMs [4]uint8
}
func (ctx *vlaUnmarshalingContext) checkRemainingLen(requiredLen int) bool {
return len(ctx.payload)-ctx.offset >= requiredLen
}
func (v *VLA) unmarshalSpatialLayers(ctx *vlaUnmarshalingContext) error {
if !ctx.checkRemainingLen(1) {
return fmt.Errorf("failed to unmarshal VLA (offset=%d): %w", ctx.offset, ErrVLATooShort)
}
v.RTPStreamID = int(ctx.payload[ctx.offset] >> 6 & 0b11)
v.RTPStreamCount = int(ctx.payload[ctx.offset]>>4&0b11) + 1
// sl_bm fields
ctx.slBMField = ctx.payload[ctx.offset] & 0b1111
ctx.offset++
if ctx.slBMField != 0 {
for streamID := 0; streamID < v.RTPStreamCount; streamID++ {
ctx.slBMs[streamID] = ctx.slBMField
}
} else {
if !ctx.checkRemainingLen((v.RTPStreamCount-1)/2 + 1) {
return fmt.Errorf("failed to unmarshal VLA (offset=%d): %w", ctx.offset, ErrVLATooShort)
}
// slX_bm fields
for streamID := 0; streamID < v.RTPStreamCount; streamID++ {
var bm uint8
if streamID%2 == 0 {
bm = ctx.payload[ctx.offset+streamID/2] >> 4 & 0b1111
} else {
bm = ctx.payload[ctx.offset+streamID/2] & 0b1111
}
ctx.slBMs[streamID] = bm
}
ctx.offset += 1 + (v.RTPStreamCount-1)/2
}
return nil
}
func (v *VLA) unmarshalTemporalLayers(ctx *vlaUnmarshalingContext) error {
if !ctx.checkRemainingLen(1) {
return fmt.Errorf("failed to unmarshal VLA (offset=%d): %w", ctx.offset, ErrVLATooShort)
}
var temporalLayerIndex int
for streamID := 0; streamID < v.RTPStreamCount; streamID++ {
for spatialID := 0; spatialID < 4; spatialID++ {
if ctx.slBMs[streamID]&(1<<spatialID) == 0 {
continue
}
if temporalLayerIndex >= 4 {
temporalLayerIndex = 0
ctx.offset++
if !ctx.checkRemainingLen(1) {
return fmt.Errorf("failed to unmarshal VLA (offset=%d): %w", ctx.offset, ErrVLATooShort)
}
}
tlCount := int(ctx.payload[ctx.offset]>>(2*(3-temporalLayerIndex))&0b11) + 1
temporalLayerIndex++
sl := SpatialLayer{
RTPStreamID: streamID,
SpatialID: spatialID,
TargetBitrates: make([]int, tlCount),
}
v.ActiveSpatialLayer = append(v.ActiveSpatialLayer, sl)
}
}
ctx.offset++
// target bitrates
for i, sl := range v.ActiveSpatialLayer {
for j := range sl.TargetBitrates {
kbps, n, err := obu.ReadLeb128(ctx.payload[ctx.offset:])
if err != nil {
return err
}
if !ctx.checkRemainingLen(int(n)) {
return fmt.Errorf("failed to unmarshal VLA (offset=%d): %w", ctx.offset, ErrVLATooShort)
}
v.ActiveSpatialLayer[i].TargetBitrates[j] = int(kbps)
ctx.offset += int(n)
}
}
return nil
}
func (v *VLA) unmarshalResolutionAndFramerate(ctx *vlaUnmarshalingContext) error {
if !ctx.checkRemainingLen(len(v.ActiveSpatialLayer) * 5) {
return fmt.Errorf("failed to unmarshal VLA (offset=%d): %w", ctx.offset, ErrVLATooShort)
}
v.HasResolutionAndFramerate = true
for i := range v.ActiveSpatialLayer {
v.ActiveSpatialLayer[i].Width = int(binary.BigEndian.Uint16(ctx.payload[ctx.offset+0:])) + 1
v.ActiveSpatialLayer[i].Height = int(binary.BigEndian.Uint16(ctx.payload[ctx.offset+2:])) + 1
v.ActiveSpatialLayer[i].Framerate = int(ctx.payload[ctx.offset+4])
ctx.offset += 5
}
return nil
}
// Unmarshal decodes VLA from a byte slice.
func (v *VLA) Unmarshal(payload []byte) (int, error) {
ctx := &vlaUnmarshalingContext{
payload: payload,
}
err := v.unmarshalSpatialLayers(ctx)
if err != nil {
return ctx.offset, err
}
// #tl fields (build the list ActiveSpatialLayer at the same time)
err = v.unmarshalTemporalLayers(ctx)
if err != nil {
return ctx.offset, err
}
if len(ctx.payload) == ctx.offset {
return ctx.offset, nil
}
// resolution & framerate (optional)
err = v.unmarshalResolutionAndFramerate(ctx)
if err != nil {
return ctx.offset, err
}
return ctx.offset, nil
}
// String makes VLA printable.
func (v VLA) String() string {
out := fmt.Sprintf("RID:%d,RTPStreamCount:%d", v.RTPStreamID, v.RTPStreamCount)
var slOut []string
for _, sl := range v.ActiveSpatialLayer {
out2 := fmt.Sprintf("RTPStreamID:%d", sl.RTPStreamID)
out2 += fmt.Sprintf(",TargetBitrates:%v", sl.TargetBitrates)
if v.HasResolutionAndFramerate {
out2 += fmt.Sprintf(",Resolution:(%d,%d)", sl.Width, sl.Height)
out2 += fmt.Sprintf(",Framerate:%d", sl.Framerate)
}
slOut = append(slOut, out2)
}
out += fmt.Sprintf(",ActiveSpatialLayers:{%s}", strings.Join(slOut, ","))
return out
}