Generalize FEC header formatting. (pt. 4)

webrtc/modules/rtp_rtcp/source/forward_error_correction_internal.h

Index: webrtc/modules/rtp_rtcp/source/forward_error_correction_internal.h
diff --git a/webrtc/modules/rtp_rtcp/source/forward_error_correction_internal.h b/webrtc/modules/rtp_rtcp/source/forward_error_correction_internal.h
index 82f02c21e56855511b509dcd5527b7cd861024bb..c61aea872c54ac612c30ba35469d914ed2571468 100644
--- a/webrtc/modules/rtp_rtcp/source/forward_error_correction_internal.h
+++ b/webrtc/modules/rtp_rtcp/source/forward_error_correction_internal.h
@@ -16,10 +16,17 @@
 
 namespace webrtc {
 
-// Packet mask size in bytes (L bit is set).
-constexpr size_t kMaskSizeLBitSet = 6;
-// Packet mask size in bytes (L bit is cleared).
-constexpr size_t kMaskSizeLBitClear = 2;
+// Maximum number of media packets that can be protected
+// by these packet masks.
+constexpr size_t kUlpfecMaxMediaPackets = 48;
+
+// Packet mask size in bytes (given L bit).
+constexpr size_t kUlpfecPacketMaskSizeLBitClear = 2;
+constexpr size_t kUlpfecPacketMaskSizeLBitSet = 6;
+
+// Convenience constants.
+constexpr size_t kUlpfecMinPacketMaskSize = kUlpfecPacketMaskSizeLBitClear;
+constexpr size_t kUlpfecMaxPacketMaskSize = kUlpfecPacketMaskSizeLBitSet;
 
 namespace internal {
 
@@ -65,6 +72,10 @@ void GeneratePacketMasks(int num_media_packets, int num_fec_packets,
                          const PacketMaskTable& mask_table,
                          uint8_t* packet_mask);
 
+// Returns the required packet mask size, given the number of sequence numbers
+// that will be covered.
+size_t PacketMaskSize(size_t num_sequence_numbers);
+
 // Inserts |num_zeros| zero columns into |new_mask| at position
 // |new_bit_index|. If the current byte of |new_mask| can't fit all zeros, the
 // byte will be filled with zeros from |new_bit_index|, but the next byte will