feat: CalcMinVersion methods for both Master and Media playlists

Implements all Compatibility Version rules except the ones for SKIP.
The sample playlists have been updated to follow the new rules.

m3u8/calcversion.go

@@ -0,0 +1,252 @@
+package m3u8
+
+import "strings"
+
+func updateMin(ver *uint8, reason *string, newVer uint8, newReason string) {
+	if newVer <= *ver { // only update if higher version
+		return
+	}
+	*ver = newVer
+	*reason = newReason
+}
+
+// CalcMinVersion returns the minimal version of the HLS protocol that is
+// required to support the playlist according to the [HLS Prococcol Version Compatibility].
+// The reason is a human-readable string explaining why the version is required.
+func (p *MasterPlaylist) CalcMinVersion() (ver uint8, reason string) {
+	ver = minVer
+	reason = "minimal version supported by this library"
+
+	// A Multivariant Playlist MUST indicate an EXT-X-VERSION of 7 or higher
+	// if it contains:
+	// *  "SERVICE" values for the INSTREAM-ID attribute of the EXT-X-MEDIA
+	for _, variant := range p.Variants {
+		for _, alt := range variant.Alternatives {
+			if strings.HasPrefix(alt.InstreamId, "SERVICE") {
+				updateMin(&ver, &reason, 7, "SERVICE value for the INSTREAM-ID attribute of the EXT-X-MEDIA")
+				break
+			}
+		}
+	}
+	// A Playlist MUST indicate an EXT-X-VERSION of 11 or higher if it contains:
+	// *  An EXT-X-DEFINE tag with a QUERYPARAM attribute.
+	for _, define := range p.Defines {
+		if define.Type == QUERYPARAM {
+			updateMin(&ver, &reason, 11, "EXT-X-DEFINE tag with a QUERYPARAM attribute")
+		}
+	}
+
+	// A Playlist MUST indicate an EXT-X-VERSION of 12 or higher if it contains:
+	// 	*  An attribute whose name starts with "REQ-".
+	// This is only defined for EXT-X-STREAM-INF and EXT-X-I-FRAME-STREAM-INF tags
+	// in the current version of the protocol.
+	for _, variant := range p.Variants {
+		if variant.ReqVideoLayout != "" {
+			updateMin(&ver, &reason, 12, "REQ- attribute")
+		}
+	}
+
+	return ver, reason
+}
+
+// CalcMinVersion returns the minimal version of the HLS protocol that is
+// required to support the playlist according to the [HLS Prococcol Version Compatibility].
+// The reason is a human-readable string explaining why the version is required.
+func (p *MediaPlaylist) CalcMinVersion() (ver uint8, reason string) {
+	ver = minVer
+	reason = "minimal version supported by this library"
+
+	// A Media Playlist MUST indicate an EXT-X-VERSION of 4 or higher if it contains:
+	// * The EXT-X-BYTERANGE tag.
+	// * The EXT-X-I-FRAMES-ONLY tag.
+
+	head := p.head
+	count := p.count
+	for i := uint(0); (i < p.winsize || p.winsize == 0) && count > 0; count-- {
+		seg := p.Segments[head]
+		head = (head + 1) % p.capacity
+		if seg == nil { // protection from badly filled chunklists
+			continue
+		}
+		if p.winsize > 0 { // skip for VOD playlists, where winsize = 0
+			i++
+		}
+		if seg.Limit > 0 {
+			updateMin(&ver, &reason, 4, "EXT-X-BYTERANGE tag")
+			break
+		}
+	}
+
+	if p.Iframe {
+		updateMin(&ver, &reason, 4, "EXT-X-I-FRAMES-ONLY tag")
+	}
+	if p.Key != nil {
+		if p.Key.Method == "SAMPLE-AES" || p.Key.Keyformat != "" || p.Key.Keyformatversions != "" {
+			updateMin(&ver, &reason, 5,
+				"EXT-X-KEY tag with a METHOD of SAMPLE-AES, KEYFORMAT or KEYFORMATVERSIONS attributes")
+		}
+	}
+	if p.Map != nil {
+		updateMin(&ver, &reason, 5, "EXT-X-MAP tag")
+	}
+
+	head = p.head
+	count = p.count
+	for i := uint(0); (i < p.winsize || p.winsize == 0) && count > 0; count-- {
+		seg := p.Segments[head]
+		head = (head + 1) % p.capacity
+		if seg == nil { // protection from badly filled chunklists
+			continue
+		}
+		if p.winsize > 0 { // skip for VOD playlists, where winsize = 0
+			i++
+		}
+		if seg.Key != nil {
+			if seg.Key.Method == "SAMPLE-AES" || seg.Key.Keyformat != "" ||
+				seg.Key.Keyformatversions != "" {
+				updateMin(&ver, &reason, 5,
+					"EXT-X-KEY tag with a METHOD of SAMPLE-AES, KEYFORMAT or KEYFORMATVERSIONS attributes")
+			}
+		}
+		if seg.Map != nil {
+			updateMin(&ver, &reason, 5, "EXT-X-MAP tag")
+			if !p.Iframe {
+				updateMin(&ver, &reason, 6,
+					"EXT-X-MAP tag in a Media Playlist that does not contain EXT-X-I-FRAMES-ONLY")
+			}
+		}
+	}
+
+	if p.Map != nil && !p.Iframe {
+		updateMin(&ver, &reason, 6,
+			"EXT-X-MAP tag in a Media Playlist that does not contain EXT-X-I-FRAMES-ONLY")
+	}
+
+	if len(p.Defines) > 0 {
+		updateMin(&ver, &reason, 8, "Variable substitution")
+	}
+
+	// EXT-X-SKIP tag triggers version 10. Not implemented yet.
+	// Also a bit unclear how to check for it since it may be generated in a request
+	/* A Playlist MUST indicate an EXT-X-VERSION of 9 or higher if it
+	   contains:
+
+	   *  The EXT-X-SKIP tag.
+
+	   A Playlist MUST indicate an EXT-X-VERSION of 10 or higher if it
+	   contains:
+
+	   *  An EXT-X-SKIP tag that replaces EXT-X-DATERANGE tags in a Playlist
+	      Delta Update.
+	*/
+
+	for _, def := range p.Defines {
+		if def.Type == QUERYPARAM {
+			updateMin(&ver, &reason, 11,
+				"EXT-X-DEFINE tag with a QUERYPARAM attribute")
+		}
+	}
+
+	return ver, reason
+}
+
+// [HLS Prococcol Version Compatibility]: https://tools.ietf.org/html/draft-pantos-hls-rfc8216bis-16#section-8
+
+/*
+From https://tools.ietf.org/html/draft-pantos-hls-rfc8216bis-16
+
+This library only supports level 3 and higher, so we don't check
+for level 1 and 2 compatibility.
+
+8.  Protocol Version Compatibility
+
+   Protocol compatibility is specified by the EXT-X-VERSION tag.  A
+   Playlist that contains tags or attributes that are not compatible
+   with protocol version 1 MUST include an EXT-X-VERSION tag.
+
+   A client MUST NOT attempt playback if it does not support the
+   protocol version specified by the EXT-X-VERSION tag, or unintended
+   behavior could occur.
+
+   A Media Playlist MUST indicate an EXT-X-VERSION of 2 or higher if it
+   contains:
+
+   *  The IV attribute of the EXT-X-KEY tag.
+
+   A Media Playlist MUST indicate an EXT-X-VERSION of 3 or higher if it
+   contains:
+
+   *  Floating-point EXTINF duration values.
+
+   A Media Playlist MUST indicate an EXT-X-VERSION of 4 or higher if it
+   contains:
+
+   *  The EXT-X-BYTERANGE tag.
+
+   *  The EXT-X-I-FRAMES-ONLY tag.
+
+   A Media Playlist MUST indicate an EXT-X-VERSION of 5 or higher if it
+   contains:
+
+   *  An EXT-X-KEY tag with a METHOD of SAMPLE-AES.
+
+   *  The KEYFORMAT and KEYFORMATVERSIONS attributes of the EXT-X-KEY
+      tag.
+
+   *  The EXT-X-MAP tag.
+
+   A Media Playlist MUST indicate an EXT-X-VERSION of 6 or higher if it
+   contains:
+
+   *  The EXT-X-MAP tag in a Media Playlist that does not contain EXT-
+      X-I-FRAMES-ONLY.
+
+   Note that in protocol version 6, the semantics of the EXT-
+   X-TARGETDURATION tag changed slightly.  In protocol version 5 and
+   earlier it indicated the maximum segment duration; in protocol
+   version 6 and later it indicates the maximum segment duration rounded
+   to the nearest integer number of seconds.
+
+   A Multivariant Playlist MUST indicate an EXT-X-VERSION of 7 or higher
+   if it contains:
+
+   *  "SERVICE" values for the INSTREAM-ID attribute of the EXT-X-MEDIA
+      tag.
+
+   A Playlist MUST indicate an EXT-X-VERSION of 8 or higher if it
+   contains:
+
+   *  Variable substitution.
+
+   A Playlist MUST indicate an EXT-X-VERSION of 9 or higher if it
+   contains:
+
+   *  The EXT-X-SKIP tag.
+
+   A Playlist MUST indicate an EXT-X-VERSION of 10 or higher if it
+   contains:
+
+   *  An EXT-X-SKIP tag that replaces EXT-X-DATERANGE tags in a Playlist
+      Delta Update.
+
+   A Playlist MUST indicate an EXT-X-VERSION of 11 or higher if it
+   contains:
+
+   *  An EXT-X-DEFINE tag with a QUERYPARAM attribute.
+
+   A Playlist MUST indicate an EXT-X-VERSION of 12 or higher if it
+   contains:
+
+   *  An attribute whose name starts with "REQ-".
+
+   The EXT-X-MEDIA tag and the AUDIO, VIDEO, and SUBTITLES attributes of
+   the EXT-X-STREAM-INF tag are backward compatible to protocol version
+   1, but playback on older clients may not be desirable.  A server MAY
+   consider indicating an EXT-X-VERSION of 4 or higher in the
+   Multivariant Playlist but is not required to do so.
+
+   The PROGRAM-ID attribute of the EXT-X-STREAM-INF and the EXT-X-I-
+   FRAME-STREAM-INF tags was removed in protocol version 6.
+
+   The EXT-X-ALLOW-CACHE tag was removed in protocol version 7.
+*/

m3u8/calcversion_test.go

@@ -0,0 +1,145 @@
+package m3u8
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/matryer/is"
+)
+
+func TestCalcMinVersionMasterPlaylist(t *testing.T) {
+	is := is.New(t)
+	pl3 := NewMasterPlaylist()
+
+	pl7 := NewMasterPlaylist()
+	pl7.Variants = append(pl7.Variants, &Variant{
+		VariantParams: VariantParams{
+			Alternatives: []*Alternative{{InstreamId: "SERVICE1"}},
+		},
+	})
+
+	pl11, err := readTestMasterPlaylist(t, "sample-playlists/master-with-defines.m3u8")
+	is.NoErr(err) // must decode sample-playlists/master-with-defines.m3u8
+
+	pl12, err := readTestMasterPlaylist(t, "sample-playlists/master-with-req-video-layout.m3u8")
+	is.NoErr(err) // must decode sample-playlists/master-with-req-video-layout.m3u8
+
+	cases := []struct {
+		playlist        Playlist
+		expectedVersion uint8
+		expectedReason  string
+	}{
+		{pl3, minVer, "minimal version supported by this library"},
+		{pl7, 7, "SERVICE value for the INSTREAM-ID attribute of the EXT-X-MEDIA"},
+		{pl11, 11, "EXT-X-DEFINE tag with a QUERYPARAM attribute"},
+		{pl12, 12, "REQ- attribute"},
+	}
+
+	for i, c := range cases {
+		t.Run(fmt.Sprintf("case-%d", i), func(t *testing.T) {
+			is := is.New(t)
+			ver, reason := c.playlist.CalcMinVersion()
+			is.Equal(ver, c.expectedVersion)
+			is.Equal(reason, c.expectedReason)
+		})
+	}
+}
+
+func TestCalcMinVersionMediaPlaylist(t *testing.T) {
+
+	is := is.New(t)
+
+	pl3, err := NewMediaPlaylist(10, 10)
+	is.NoErr(err) // must create media playlist
+
+	pl4ByteRange, err := readTestMediaPlaylist(t, "sample-playlists/media-playlist-with-byterange.m3u8")
+	is.NoErr(err) // must decode sample-playlists/media-playlist-with-byterange.m3u8
+
+	pl4IframesOnly, err := readTestMediaPlaylist(t, "sample-playlists/media-playlist-with-iframes-only.m3u8")
+	is.NoErr(err) // must decode sample-playlists/media-playlist-with-iframes-only.m3u8
+
+	pl5IframesOnlyAndMap, err := readTestMediaPlaylist(t, "sample-playlists/media-playlist-with-iframes-only-and-map.m3u8")
+	is.NoErr(err) // must decode sample-playlists/media-playlist-with-iframes-only-and-map.m3u8
+
+	pl5SampleAES, err := readTestMediaPlaylist(t, "sample-playlists/media-playlist-with-key.m3u8")
+	is.NoErr(err) // must decode sample-playlists/media-playlist-with-key.m3u8
+
+	pl6Fmp4, err := readTestMediaPlaylist(t, "sample-playlists/media-playlist-fmp4.m3u8")
+	is.NoErr(err) // must decode sample-playlists/media-playlist-fmp4.m3u8
+
+	pl8VariableSubstitution, err := readTestMediaPlaylist(t, "sample-playlists/media-playlist-with-defines.m3u8")
+	is.NoErr(err) // must decode sample-playlists/media-playlist-with-defines.m3u8
+
+	pl11QueryParam, err := readTestMediaPlaylist(t, "sample-playlists/media-playlist-with-queryparam.m3u8")
+	is.NoErr(err) // must decode sample-playlists/media-playlist-with-queryparam.m3u8
+
+	cases := []struct {
+		playlist        Playlist
+		expectedVersion uint8
+		expectedReason  string
+	}{
+		{pl3, minVer, "minimal version supported by this library"},
+		{pl4ByteRange, 4, "EXT-X-BYTERANGE tag"},
+		{pl4IframesOnly, 4, "EXT-X-I-FRAMES-ONLY tag"},
+		{pl5IframesOnlyAndMap, 5, "EXT-X-MAP tag"},
+		{pl5SampleAES, 5, "EXT-X-KEY tag with a METHOD of SAMPLE-AES, KEYFORMAT or KEYFORMATVERSIONS attributes"},
+		{pl6Fmp4, 6, "EXT-X-MAP tag in a Media Playlist that does not contain EXT-X-I-FRAMES-ONLY"},
+		{pl8VariableSubstitution, 8, "Variable substitution"},
+		{pl11QueryParam, 11, "EXT-X-DEFINE tag with a QUERYPARAM attribute"},
+	}
+
+	for i, c := range cases {
+		t.Run(fmt.Sprintf("case-%d", i), func(t *testing.T) {
+			is := is.New(t)
+			ver, reason := c.playlist.CalcMinVersion()
+			is.Equal(ver, c.expectedVersion)
+			is.Equal(reason, c.expectedReason)
+		})
+	}
+}
+
+func readTestPlaylist(t *testing.T, fileName string) Playlist {
+	t.Helper()
+	f, err := os.Open(fileName)
+	if err != nil {
+		t.Fail()
+	}
+	defer f.Close()
+
+	p, _, err := DecodeFrom(bufio.NewReader(f), false)
+	if err != nil {
+		t.Fail()
+	}
+	return p
+}
+
+func TestAllPlaylistVersions(t *testing.T) {
+	is := is.New(t)
+
+	// Read all m3u8 files in sample-playlists directory
+	files, err := os.ReadDir("sample-playlists")
+	is.NoErr(err)
+
+	for _, file := range files {
+		fName := file.Name()
+		if !strings.HasSuffix(fName, ".m3u8") {
+			continue
+		}
+
+		t.Run(fName, func(t *testing.T) {
+			path := "sample-playlists/" + fName
+
+			p := readTestPlaylist(t, path)
+
+			minVer, reason := p.CalcMinVersion()
+			actualVer := p.Version()
+			if minVer > actualVer {
+				t.Errorf("Playlist %s: CalcMinVersion=%d but Version=%d (reason: %s)",
+					fName, minVer, actualVer, reason)
+			}
+		})
+	}
+}