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gBillal merged 1 commit into from
May 6, 2026
Merged

feat(h264): add parameter sets iterator to decoder configuration record #3

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125 changes: 99 additions & 26 deletions src/h264.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,10 @@ pub const NalType = enum(u5) {
fu_b,
unspecified30,
unspecified31,

pub inline fn isKeyframe(self: NalType) bool {
return self == .idr;
}
};

/// Describes the NAL unit header, which is the first byte of a NAL unit.
Expand Down Expand Up @@ -329,6 +333,9 @@ pub const DecoderConfigurationRecord = struct {
profile_compatibility: u8,
avc_level_indication: u8,
length_size: u8,
ps_bytes: []const u8 = &.{},

pub const H264Error = error{InvalidH264DCR};

pub fn initFromSps(sps: *const Sps) DecoderConfigurationRecord {
return DecoderConfigurationRecord{
Expand All @@ -339,48 +346,82 @@ pub const DecoderConfigurationRecord = struct {
};
}

pub fn parse(data: []const u8) !DecoderConfigurationRecord {
var reader = std.Io.Reader.fixed(data);
_ = try reader.takeByte();
pub fn parse(data: []const u8) H264Error!DecoderConfigurationRecord {
if (data.len < 7) return error.InvalidH264DCR;

return DecoderConfigurationRecord{
.avc_profile_indication = try reader.takeByte(),
.profile_compatibility = try reader.takeByte(),
.avc_level_indication = try reader.takeByte(),
.length_size = (try reader.takeByte() & 0x03) + 1,
.avc_profile_indication = data[1],
.profile_compatibility = data[2],
.avc_level_indication = data[3],
.length_size = (data[4] & 0x03) + 1,
.ps_bytes = data[5..],
};
}

pub const Writer = struct {
writer: *std.Io.Writer,
pub fn iterateParameterSets(self: *const DecoderConfigurationRecord) Iterator {
return .init(self.ps_bytes);
}

pub fn init(writer: *std.Io.Writer) Writer {
return Writer{ .writer = writer };
pub fn writer(self: *const DecoderConfigurationRecord, w: *std.Io.Writer) !Writer {
try w.writeByte(1); // configurationVersion
try w.writeByte(self.avc_profile_indication);
try w.writeByte(self.profile_compatibility);
try w.writeByte(self.avc_level_indication);
try w.writeByte(0xFC | (self.length_size - 1));
return .{ .writer = w };
}

pub const Iterator = struct {
reader: std.Io.Reader,
nal_type: NalType,
count: u8,

pub fn init(bytes: []const u8) Iterator {
return .{
.reader = std.Io.Reader.fixed(bytes[1..]),
.nal_type = .sps,
.count = bytes[0] & 0x1F,
};
}

pub fn write(self: *@This(), config: *const DecoderConfigurationRecord) !void {
try self.writer.writeByte(1); // configurationVersion
try self.writer.writeByte(config.avc_profile_indication);
try self.writer.writeByte(config.profile_compatibility);
try self.writer.writeByte(config.avc_level_indication);
try self.writer.writeByte(0xFC | (config.length_size - 1));
pub fn next(it: *Iterator) H264Error!?[]const u8 {
if (it.count == 0) {
switch (it.nal_type) {
.sps => {
it.nal_type = .pps;
it.count = it.reader.takeByte() catch return error.InvalidH264DCR;
return it.next();
},
.pps => return null,
else => unreachable,
}
}

const nal_size = it.reader.takeInt(u16, .big) catch return error.InvalidH264DCR;
const result = it.reader.take(nal_size) catch return error.InvalidH264DCR;
it.count -= 1;
return result;
}
};

pub const Writer = struct {
writer: *std.Io.Writer,

pub fn writeSpsCount(self: *@This(), count: u8) !void {
pub fn writeSpsCount(self: *Writer, count: u8) !void {
std.debug.assert(count <= 31);
try self.writer.writeByte(0xE0 | (count & 0x1F));
}

pub fn writePpsCount(self: *@This(), count: u8) !void {
pub fn writePpsCount(self: *Writer, count: u8) !void {
try self.writer.writeByte(count);
}

pub fn writeNalUnit(self: *@This(), nal_data: []const u8) !void {
pub fn writeNalUnit(self: *Writer, nal_data: []const u8) !void {
try self.writer.writeInt(u16, @intCast(nal_data.len), .big);
try self.writer.writeAll(nal_data);
}

pub fn writeBase64NalUnit(self: *@This(), nal_data: []const u8) !void {
pub fn writeBase64NalUnit(self: *Writer, nal_data: []const u8) !void {
var decoder = std.base64.standard.Decoder;

const nal_size = try decoder.calcSizeForSlice(nal_data);
Expand All @@ -392,7 +433,7 @@ pub const DecoderConfigurationRecord = struct {
};

test "parse valid configuration" {
const data = [_]u8{ 1, 100, 0, 40, 0xFF, 0x00 };
const data = [_]u8{ 1, 100, 0, 40, 0xFF, 0xE0, 0x00 };
const config = try DecoderConfigurationRecord.parse(&data);

try std.testing.expect(config.avc_profile_indication == 100);
Expand All @@ -413,8 +454,7 @@ pub const DecoderConfigurationRecord = struct {

var buf: [64]u8 = undefined;
var w = std.Io.Writer.fixed(&buf);
var dcr_writer = DecoderConfigurationRecord.Writer.init(&w);
try dcr_writer.write(&config);
var dcr_writer = try config.writer(&w);
try dcr_writer.writeSpsCount(1);
try dcr_writer.writeNalUnit(&sps_nal);
try dcr_writer.writePpsCount(1);
Expand All @@ -438,8 +478,7 @@ pub const DecoderConfigurationRecord = struct {

var buf: [64]u8 = undefined;
var w = std.Io.Writer.fixed(&buf);
var dcr_writer = DecoderConfigurationRecord.Writer.init(&w);
try dcr_writer.write(&original);
var dcr_writer = try original.writer(&w);
try dcr_writer.writeSpsCount(0);
try dcr_writer.writePpsCount(0);

Expand All @@ -465,6 +504,40 @@ pub const DecoderConfigurationRecord = struct {
try std.testing.expectEqual(sps.level_idc, config.avc_level_indication);
try std.testing.expectEqual(@as(u8, 4), config.length_size);
}

test "iterator parameter sets" {
const bytes = [_]u8{
0x01, 0x4d, 0x40, 0x1f, 0xff, 0xe1, 0x00,
0x1d, 0x67, 0x4d, 0x40, 0x1f, 0xec, 0xa0,
0x6c, 0x1f, 0xf2, 0x44, 0x7f, 0xe1, 0xe2,
0x01, 0xe2, 0xa2, 0x00, 0x00, 0x03, 0x00,
0x64, 0x00, 0x00, 0x12, 0xbc, 0x1e, 0x30,
0x63, 0x2c, 0x01, 0x00, 0x04, 0x68, 0xef,
0x86, 0xf2,
};

const dcr = try parse(&bytes);
try std.testing.expectEqual(77, dcr.avc_profile_indication);
try std.testing.expectEqual(64, dcr.profile_compatibility);
try std.testing.expectEqual(31, dcr.avc_level_indication);
try std.testing.expectEqual(4, dcr.length_size);

const expected_sps = [_]u8{
0x67, 0x4d, 0x40, 0x1f, 0xec,
0xa0, 0x6c, 0x1f, 0xf2, 0x44,
0x7f, 0xe1, 0xe2, 0x01, 0xe2,
0xa2, 0x00, 0x00, 0x03, 0x00,
0x64, 0x00, 0x00, 0x12, 0xbc,
0x1e, 0x30, 0x63, 0x2c,
};

const expected_pps = [_]u8{ 0x68, 0xef, 0x86, 0xf2 };

var it = dcr.iterateParameterSets();
try std.testing.expectEqualSlices(u8, &expected_sps, (try it.next()).?);
try std.testing.expectEqualSlices(u8, &expected_pps, (try it.next()).?);
try std.testing.expectEqual(null, try it.next());
}
};

const ParameterSetReader = struct {
Expand Down
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