mp3: Error if > 5 unique header configs

Hopefully make it less likely to missprobe

format/format.go

@@ -165,3 +165,12 @@ type MPEGASCOut struct {
 type AACFrameIn struct {
 	ObjectType int
 }
+
+type MP3FrameOut struct {
+	MPEGVersion      int
+	ProtectionAbsent bool
+	BitRate          int
+	SampleRate       int
+	ChannelsIndex    int
+	ChannelModeIndex int
+}

format/mp3/mp3.go

@@ -1,9 +1,10 @@
 package mp3
 
 // TODO: vbri
-// TODO: mime audio/mpeg
 
 import (
+	"fmt"
+
 	"github.com/wader/fq/format"
 	"github.com/wader/fq/format/registry"
 	"github.com/wader/fq/pkg/decode"
@@ -33,6 +34,17 @@ func init() {
 }
 
 func mp3Decode(d *decode.D, in interface{}) interface{} {
+	// things in a mp3 stream usually have few unique combinations of.
+	// does not include bitrate on purpose
+	type headerConfig struct {
+		MPEGVersion      int
+		ProtectionAbsent bool
+		SampleRate       int
+		ChannelsIndex    int
+		ChannelModeIndex int
+	}
+	uniqueHeaderConfigs := map[headerConfig]struct{}{}
+
 	// there are mp3s files in the wild with multiple headers, two id3v2 tags etc
 	d.FieldArray("headers", func(d *decode.D) {
 		for d.NotEnd() {
@@ -59,16 +71,33 @@ func mp3Decode(d *decode.D, in interface{}) interface{} {
 				d.SeekRel(syncLen)
 			}
 
-			if dv, _, _ := d.FieldTryFormat("frame", mp3Frame, nil); dv == nil {
+			dv, v, _ := d.FieldTryFormat("frame", mp3Frame, nil)
+			if dv == nil {
 				decodeFailures++
 				d.SeekRel(8)
 				continue
 			}
+			mfo, ok := v.(format.MP3FrameOut)
+			if !ok {
+				panic(fmt.Sprintf("expected MP3FrameOut got %#+v", v))
+			}
+			uniqueHeaderConfigs[headerConfig{
+				MPEGVersion:      mfo.MPEGVersion,
+				ProtectionAbsent: mfo.ProtectionAbsent,
+				SampleRate:       mfo.SampleRate,
+				ChannelsIndex:    mfo.ChannelsIndex,
+				ChannelModeIndex: mfo.ChannelModeIndex,
+			}] = struct{}{}
+
 			lastValidEnd = d.Pos()
 			validFrames++
+
+			if len(uniqueHeaderConfigs) > 5 {
+				d.Errorf("too many unique header configurations")
+			}
 		}
 	})
-	// TODO: better validate
+
 	if validFrames == 0 || (validFrames < 2 && decodeFailures > 0) {
 		d.Errorf("no frames found")
 	}

format/mpeg/mp3_frame.go

@@ -147,8 +147,11 @@ func frameDecode(d *decode.D, in interface{}) interface{} {
 	var crcBytes int64
 	var mpegVersionNr uint64
 	var mpegLayerNr uint64
+	var protectionAbsent bool
 	var bitRate uint64
 	var sampleRate uint64
+	var channelsIndex uint64
+	var channelModeIndex uint64
 	var mainDataEnd uint64
 	var crcValue *decode.Value
 
@@ -239,14 +242,14 @@ func frameDecode(d *decode.D, in interface{}) interface{} {
 			1: "Padded",
 		}), d.Bin)
 		d.FieldU1("private")
-		channelsIndex := d.FieldU2("channels", d.MapUToStrSym(decode.UToStr{
+		channelsIndex = d.FieldU2("channels", d.MapUToStrSym(decode.UToStr{
 			0b00: "Stereo",
 			0b01: "Joint stereo",
 			0b10: "Dual",
 			0b11: "Mono",
 		}), d.Bin)
 		isStereo = channelsIndex != 0b11
-		d.FieldU2("channel_mode", d.MapUToStrSym(decode.UToStr{
+		channelModeIndex = d.FieldU2("channel_mode", d.MapUToStrSym(decode.UToStr{
 			0b00: "None",
 			0b01: "Intensity stereo",
 			0b10: "MS stereo",
@@ -393,5 +396,12 @@ func frameDecode(d *decode.D, in interface{}) interface{} {
 	}
 	d.FieldValueRaw("crc_calculated", crcHash.Sum(nil), d.RawHex)
 
-	return nil
+	return format.MP3FrameOut{
+		MPEGVersion:      int(mpegVersionNr),
+		ProtectionAbsent: protectionAbsent,
+		BitRate:          int(bitRate),
+		SampleRate:       int(sampleRate),
+		ChannelsIndex:    int(channelModeIndex),
+		ChannelModeIndex: int(channelModeIndex),
+	}
 }