feat(mcap): add paced replay tooling

CMakeLists.txt

@@ -210,3 +210,30 @@ target_link_libraries(mcap_reader_tester PRIVATE cvmmap_streamer_protobuf)
 if (TARGET PkgConfig::PROTOBUF_PKG)
 	target_link_libraries(mcap_reader_tester PRIVATE PkgConfig::PROTOBUF_PKG)
 endif()
+
+add_executable(mcap_replay_tester src/testers/mcap_replay_tester.cpp)
+target_include_directories(mcap_replay_tester
+	PRIVATE
+		"${CMAKE_CURRENT_LIST_DIR}/include"
+		"${CMAKE_CURRENT_LIST_DIR}/lib/CLI11/include"
+		"${CMAKE_CURRENT_LIST_DIR}/lib/mcap/include"
+		"${CVMMAP_PROXY_INCLUDE_DIR}"
+		"${CMAKE_CURRENT_BINARY_DIR}")
+target_link_libraries(mcap_replay_tester
+	PRIVATE
+		Threads::Threads
+		cvmmap_streamer_foxglove_proto
+		PkgConfig::ZSTD
+		PkgConfig::LZ4)
+if (TARGET spdlog::spdlog)
+	target_link_libraries(mcap_replay_tester PRIVATE spdlog::spdlog)
+elseif (TARGET spdlog)
+	target_link_libraries(mcap_replay_tester PRIVATE spdlog)
+endif()
+if (TARGET CLI11::CLI11)
+	target_link_libraries(mcap_replay_tester PRIVATE CLI11::CLI11)
+endif()
+target_link_libraries(mcap_replay_tester PRIVATE cvmmap_streamer_protobuf)
+if (TARGET PkgConfig::PROTOBUF_PKG)
+	target_link_libraries(mcap_replay_tester PRIVATE PkgConfig::PROTOBUF_PKG)
+endif()

include/cvmmap_streamer/record/mcap_record_sink.hpp

@@ -21,7 +21,12 @@ public:
 	McapRecordSink &operator=(McapRecordSink &&other) noexcept;
 
 	[[nodiscard]]
-	static std::expected<McapRecordSink, std::string> create(const RuntimeConfig &config);
+	static std::expected<McapRecordSink, std::string> create(
+		const RuntimeConfig &config,
+		const encode::EncodedStreamInfo &stream_info);
+
+	[[nodiscard]]
+	std::expected<void, std::string> update_stream_info(const encode::EncodedStreamInfo &stream_info);
 
 	[[nodiscard]]
 	std::expected<void, std::string> write_access_unit(const encode::EncodedAccessUnit &access_unit);

scripts/replay_mcap.sh

@@ -0,0 +1,68 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)"
+BUILD_DIR="${BUILD_DIR:-$ROOT_DIR/build}"
+REPLAY_BIN="${REPLAY_BIN:-$BUILD_DIR/mcap_replay_tester}"
+FFPLAY_BIN="${FFPLAY_BIN:-ffplay}"
+FFPLAY_ARGS="${FFPLAY_ARGS:-}"
+
+usage() {
+	cat <<'EOF'
+Usage:
+  replay_mcap.sh <input.mcap> [h264|h265]
+
+This replays MCAP video using the recorded timestamps and pipes frames to ffplay.
+The optional codec argument defaults to h264. Extra ffplay flags may be supplied
+via FFPLAY_ARGS, for example: FFPLAY_ARGS='-window_title replay'.
+EOF
+}
+
+if [[ "${1:-}" == "--help" || "${1:-}" == "-h" ]]; then
+	usage
+	exit 0
+fi
+
+if [[ $# -lt 1 || $# -gt 2 ]]; then
+	usage >&2
+	exit 1
+fi
+
+INPUT_PATH="$1"
+FORMAT="${2:-h264}"
+if [[ "$FORMAT" != "h264" && "$FORMAT" != "h265" ]]; then
+	echo "unsupported format: $FORMAT (expected h264 or h265)" >&2
+	exit 1
+fi
+
+if [[ ! -f "$INPUT_PATH" ]]; then
+	echo "input MCAP not found: $INPUT_PATH" >&2
+	exit 1
+fi
+if [[ ! -x "$REPLAY_BIN" ]]; then
+	echo "replay binary not found: $REPLAY_BIN" >&2
+	exit 1
+fi
+if ! command -v "$FFPLAY_BIN" >/dev/null 2>&1; then
+	echo "ffplay not found: $FFPLAY_BIN" >&2
+	exit 1
+fi
+
+extra_args=()
+if [[ -n "$FFPLAY_ARGS" ]]; then
+	# shellcheck disable=SC2206
+	extra_args=($FFPLAY_ARGS)
+fi
+
+cmd=(
+	"$REPLAY_BIN"
+	"$INPUT_PATH"
+	--expect-format "$FORMAT"
+	--ffplay-path "$FFPLAY_BIN"
+)
+
+for arg in "${extra_args[@]}"; do
+	cmd+=(--ffplay-arg "$arg")
+done
+
+"${cmd[@]}"

src/pipeline/pipeline_runtime.cpp

@@ -331,15 +331,6 @@ int run_pipeline(const RuntimeConfig &config) {
 		rtp_publisher.emplace(std::move(*created));
 	}
 
-	if (config.record.mcap.enabled) {
-		auto created = record::McapRecordSink::create(config);
-		if (!created) {
-			spdlog::error("pipeline MCAP sink init failed: {}", created.error());
-			return exit_code(PipelineExitCode::InitializationError);
-		}
-		mcap_sink.emplace(std::move(*created));
-	}
-
 	PipelineStats stats{};
 	metrics::IngestEmitLatencyTracker latency_tracker{};
 	bool producer_offline{false};
@@ -386,6 +377,30 @@ int run_pipeline(const RuntimeConfig &config) {
 			}
 			rtmp_output.emplace(std::move(*created));
 		}
+		if (config.record.mcap.enabled) {
+			auto stream_info = (*backend)->stream_info();
+			if (!stream_info) {
+				return unexpected_error(
+					stream_info.error().code,
+					"pipeline MCAP stream info unavailable: " + format_error(stream_info.error()));
+			}
+			if (!mcap_sink) {
+				auto created = record::McapRecordSink::create(config, *stream_info);
+				if (!created) {
+					return unexpected_error(
+						ERR_INTERNAL,
+						"pipeline MCAP sink init failed: " + created.error());
+				}
+				mcap_sink.emplace(std::move(*created));
+			} else {
+				auto updated = mcap_sink->update_stream_info(*stream_info);
+				if (!updated) {
+					return unexpected_error(
+						ERR_INTERNAL,
+						"pipeline MCAP stream update failed: " + updated.error());
+				}
+			}
+		}
 		started = true;
 		restart_pending = false;
 		restart_target_info.reset();

src/record/mcap_record_sink.cpp

@@ -12,9 +12,11 @@
 #include <cstdint>
 #include <expected>
 #include <memory>
+#include <span>
 #include <string>
 #include <string_view>
 #include <utility>
+#include <vector>
 
 namespace cvmmap_streamer::record {
 
@@ -46,6 +48,134 @@ google::protobuf::Timestamp to_proto_timestamp(std::uint64_t timestamp_ns) {
 	return timestamp;
 }
 
+void append_start_code(std::vector<std::uint8_t> &output) {
+	output.push_back(0x00);
+	output.push_back(0x00);
+	output.push_back(0x00);
+	output.push_back(0x01);
+}
+
+[[nodiscard]]
+std::expected<std::uint16_t, std::string> read_be16(std::span<const std::uint8_t> bytes, std::size_t offset) {
+	if (offset + 2 > bytes.size()) {
+		return std::unexpected("decoder config truncated");
+	}
+	return static_cast<std::uint16_t>((static_cast<std::uint16_t>(bytes[offset]) << 8) | bytes[offset + 1]);
+}
+
+[[nodiscard]]
+bool looks_like_annexb(std::span<const std::uint8_t> bytes) {
+	if (bytes.size() >= 4 &&
+		bytes[0] == 0x00 &&
+		bytes[1] == 0x00 &&
+		bytes[2] == 0x00 &&
+		bytes[3] == 0x01) {
+		return true;
+	}
+	return bytes.size() >= 3 &&
+		   bytes[0] == 0x00 &&
+		   bytes[1] == 0x00 &&
+		   bytes[2] == 0x01;
+}
+
+[[nodiscard]]
+std::expected<std::vector<std::uint8_t>, std::string> avcc_to_annexb(std::span<const std::uint8_t> decoder_config) {
+	if (decoder_config.size() < 7 || decoder_config[0] != 1) {
+		return std::unexpected("invalid AVC decoder config");
+	}
+
+	std::vector<std::uint8_t> annexb{};
+	std::size_t offset = 5;
+	const auto sps_count = static_cast<std::size_t>(decoder_config[offset++] & 0x1fu);
+	for (std::size_t i = 0; i < sps_count; ++i) {
+		auto size = read_be16(decoder_config, offset);
+		if (!size) {
+			return std::unexpected(size.error());
+		}
+		offset += 2;
+		if (offset + *size > decoder_config.size()) {
+			return std::unexpected("invalid AVC decoder config payload");
+		}
+		append_start_code(annexb);
+		annexb.insert(annexb.end(), decoder_config.begin() + static_cast<std::ptrdiff_t>(offset), decoder_config.begin() + static_cast<std::ptrdiff_t>(offset + *size));
+		offset += *size;
+	}
+
+	if (offset >= decoder_config.size()) {
+		return std::unexpected("invalid AVC decoder config: missing PPS count");
+	}
+	const auto pps_count = static_cast<std::size_t>(decoder_config[offset++]);
+	for (std::size_t i = 0; i < pps_count; ++i) {
+		auto size = read_be16(decoder_config, offset);
+		if (!size) {
+			return std::unexpected(size.error());
+		}
+		offset += 2;
+		if (offset + *size > decoder_config.size()) {
+			return std::unexpected("invalid AVC decoder config payload");
+		}
+		append_start_code(annexb);
+		annexb.insert(annexb.end(), decoder_config.begin() + static_cast<std::ptrdiff_t>(offset), decoder_config.begin() + static_cast<std::ptrdiff_t>(offset + *size));
+		offset += *size;
+	}
+
+	return annexb;
+}
+
+[[nodiscard]]
+std::expected<std::vector<std::uint8_t>, std::string> hvcc_to_annexb(std::span<const std::uint8_t> decoder_config) {
+	if (decoder_config.size() < 23 || decoder_config[0] != 1) {
+		return std::unexpected("invalid HEVC decoder config");
+	}
+
+	std::vector<std::uint8_t> annexb{};
+	std::size_t offset = 22;
+	const auto array_count = static_cast<std::size_t>(decoder_config[offset++]);
+	for (std::size_t array_index = 0; array_index < array_count; ++array_index) {
+		if (offset + 3 > decoder_config.size()) {
+			return std::unexpected("invalid HEVC decoder config arrays");
+		}
+		offset += 1;
+		auto nal_count = read_be16(decoder_config, offset);
+		if (!nal_count) {
+			return std::unexpected(nal_count.error());
+		}
+		offset += 2;
+
+		for (std::size_t nal_index = 0; nal_index < *nal_count; ++nal_index) {
+			auto nal_size = read_be16(decoder_config, offset);
+			if (!nal_size) {
+				return std::unexpected(nal_size.error());
+			}
+			offset += 2;
+			if (offset + *nal_size > decoder_config.size()) {
+				return std::unexpected("invalid HEVC decoder config payload");
+			}
+			append_start_code(annexb);
+			annexb.insert(annexb.end(), decoder_config.begin() + static_cast<std::ptrdiff_t>(offset), decoder_config.begin() + static_cast<std::ptrdiff_t>(offset + *nal_size));
+			offset += *nal_size;
+		}
+	}
+
+	return annexb;
+}
+
+[[nodiscard]]
+std::expected<std::vector<std::uint8_t>, std::string> decoder_config_to_annexb(
+	CodecType codec,
+	std::span<const std::uint8_t> decoder_config) {
+	if (decoder_config.empty()) {
+		return std::vector<std::uint8_t>{};
+	}
+	if (looks_like_annexb(decoder_config)) {
+		return std::vector<std::uint8_t>(decoder_config.begin(), decoder_config.end());
+	}
+	if (codec == CodecType::H265) {
+		return hvcc_to_annexb(decoder_config);
+	}
+	return avcc_to_annexb(decoder_config);
+}
+
 }
 
 struct McapRecordSink::State {
@@ -54,6 +184,8 @@ struct McapRecordSink::State {
 	std::string frame_id{};
 	mcap::ChannelId channel_id{0};
 	std::uint32_t sequence{0};
+	CodecType codec{CodecType::H264};
+	std::vector<std::uint8_t> keyframe_preamble{};
 };
 
 McapRecordSink::~McapRecordSink() {
@@ -74,7 +206,9 @@ McapRecordSink &McapRecordSink::operator=(McapRecordSink &&other) noexcept {
 	return *this;
 }
 
-std::expected<McapRecordSink, std::string> McapRecordSink::create(const RuntimeConfig &config) {
+std::expected<McapRecordSink, std::string> McapRecordSink::create(
+	const RuntimeConfig &config,
+	const encode::EncodedStreamInfo &stream_info) {
 	McapRecordSink sink{};
 	auto state = std::make_unique<State>();
 	state->path = config.record.mcap.path;
@@ -101,9 +235,27 @@ std::expected<McapRecordSink, std::string> McapRecordSink::create(const RuntimeC
 	state->channel_id = channel.id;
 
 	sink.state_ = state.release();
+	auto update = sink.update_stream_info(stream_info);
+	if (!update) {
+		sink.close();
+		return std::unexpected(update.error());
+	}
 	return sink;
 }
 
+std::expected<void, std::string> McapRecordSink::update_stream_info(const encode::EncodedStreamInfo &stream_info) {
+	if (state_ == nullptr) {
+		return std::unexpected("MCAP sink is not open");
+	}
+	auto decoder_config_annexb = decoder_config_to_annexb(stream_info.codec, stream_info.decoder_config);
+	if (!decoder_config_annexb) {
+		return std::unexpected("failed to prepare MCAP keyframe decoder config: " + decoder_config_annexb.error());
+	}
+	state_->codec = stream_info.codec;
+	state_->keyframe_preamble = std::move(*decoder_config_annexb);
+	return {};
+}
+
 std::expected<void, std::string> McapRecordSink::write_access_unit(const encode::EncodedAccessUnit &access_unit) {
 	if (state_ == nullptr) {
 		return std::unexpected("MCAP sink is not open");
@@ -113,9 +265,15 @@ std::expected<void, std::string> McapRecordSink::write_access_unit(const encode:
 	*message.mutable_timestamp() = to_proto_timestamp(access_unit.source_timestamp_ns);
 	message.set_frame_id(state_->frame_id);
 	message.set_format(codec_format(access_unit.codec));
+	std::vector<std::uint8_t> payload{};
+	if (access_unit.keyframe && !state_->keyframe_preamble.empty()) {
+		payload.reserve(state_->keyframe_preamble.size() + access_unit.annexb_bytes.size());
+		payload.insert(payload.end(), state_->keyframe_preamble.begin(), state_->keyframe_preamble.end());
+	}
+	payload.insert(payload.end(), access_unit.annexb_bytes.begin(), access_unit.annexb_bytes.end());
 	message.set_data(
-		reinterpret_cast<const char *>(access_unit.annexb_bytes.data()),
-		static_cast<int>(access_unit.annexb_bytes.size()));
+		reinterpret_cast<const char *>(payload.data()),
+		static_cast<int>(payload.size()));
 
 	std::string serialized{};
 	if (!message.SerializeToString(&serialized)) {

src/testers/mcap_reader_tester.cpp

@@ -7,6 +7,7 @@
 
 #include <cstdint>
 #include <expected>
+#include <fstream>
 #include <iostream>
 #include <optional>
 #include <string>
@@ -25,6 +26,7 @@ enum class TesterExitCode : int {
 	FormatMismatch = 7,
 	EmptyPayload = 8,
 	ThresholdError = 9,
+	DumpError = 10,
 };
 
 [[nodiscard]]
@@ -36,6 +38,7 @@ struct Config {
 	std::string input_path{};
 	std::optional<std::string> expected_topic{};
 	std::optional<std::string> expected_format{};
+	std::optional<std::string> dump_annexb_output{};
 	std::uint32_t min_messages{1};
 };
 
@@ -46,6 +49,7 @@ std::expected<Config, int> parse_args(int argc, char **argv) {
 	app.add_option("input", config.input_path, "Input MCAP path")->required();
 	app.add_option("--expect-topic", config.expected_topic, "Expected MCAP topic");
 	app.add_option("--expect-format", config.expected_format, "Expected CompressedVideo format");
+	app.add_option("--dump-annexb-output", config.dump_annexb_output, "Write concatenated CompressedVideo.data payloads to a file");
 	app.add_option("--min-messages", config.min_messages, "Minimum expected message count")->check(CLI::PositiveNumber);
 
 	try {
@@ -74,6 +78,15 @@ int main(int argc, char **argv) {
 	std::uint64_t message_count{0};
 	std::uint64_t previous_log_time{0};
 	bool saw_log_time{false};
+	std::optional<std::ofstream> dump_stream{};
+	if (config->dump_annexb_output) {
+		dump_stream.emplace(*config->dump_annexb_output, std::ios::binary | std::ios::trunc);
+		if (!dump_stream->is_open()) {
+			spdlog::error("failed to open dump output '{}'", *config->dump_annexb_output);
+			reader.close();
+			return exit_code(TesterExitCode::DumpError);
+		}
+	}
 
 	auto message_view = reader.readMessages();
 	for (auto it = message_view.begin(); it != message_view.end(); ++it) {
@@ -117,6 +130,14 @@ int main(int argc, char **argv) {
 			reader.close();
 			return exit_code(TesterExitCode::EmptyPayload);
 		}
+		if (dump_stream) {
+			dump_stream->write(message.data().data(), static_cast<std::streamsize>(message.data().size()));
+			if (!dump_stream->good()) {
+				spdlog::error("failed to write Annex B dump to '{}'", *config->dump_annexb_output);
+				reader.close();
+				return exit_code(TesterExitCode::DumpError);
+			}
+		}
 
 		previous_log_time = it->message.logTime;
 		saw_log_time      = true;

src/testers/mcap_replay_tester.cpp

@@ -0,0 +1,298 @@
+#define MCAP_IMPLEMENTATION
+#include <mcap/reader.hpp>
+
+#include <foxglove/CompressedVideo.pb.h>
+
+#include <CLI/CLI.hpp>
+
+#include <chrono>
+#include <cstdint>
+#include <expected>
+#include <optional>
+#include <span>
+#include <string>
+#include <string_view>
+#include <system_error>
+#include <thread>
+#include <vector>
+
+#include <cerrno>
+#include <cstring>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <spdlog/spdlog.h>
+
+namespace {
+
+enum class TesterExitCode : int {
+	Success = 0,
+	OpenError = 2,
+	SchemaError = 3,
+	TopicMismatch = 4,
+	ParseError = 5,
+	FormatMismatch = 6,
+	EmptyPayload = 7,
+	ProcessError = 8,
+	WriteError = 9,
+	WaitError = 10,
+};
+
+[[nodiscard]]
+constexpr int exit_code(TesterExitCode code) {
+	return static_cast<int>(code);
+}
+
+struct Config {
+	std::string input_path{};
+	std::optional<std::string> expected_topic{};
+	std::string expected_format{"h264"};
+	std::string ffplay_path{"ffplay"};
+	std::vector<std::string> ffplay_args{};
+	double speed{1.0};
+	bool no_pace{false};
+};
+
+struct ReplayMessage {
+	std::uint64_t timestamp_ns{0};
+	std::vector<std::uint8_t> payload{};
+};
+
+[[nodiscard]]
+std::expected<Config, int> parse_args(int argc, char **argv) {
+	Config config{};
+	CLI::App app{"mcap_replay_tester - replay foxglove.CompressedVideo MCAP with recorded pacing"};
+	app.add_option("input", config.input_path, "Input MCAP path")->required();
+	app.add_option("--expect-topic", config.expected_topic, "Expected MCAP topic");
+	app.add_option("--expect-format", config.expected_format, "Expected CompressedVideo format")
+		->check(CLI::IsMember({"h264", "h265"}));
+	app.add_option("--ffplay-path", config.ffplay_path, "ffplay binary path");
+	app.add_option("--ffplay-arg", config.ffplay_args, "Extra ffplay argument (repeatable)");
+	app.add_option("--speed", config.speed, "Playback speed multiplier")->check(CLI::PositiveNumber);
+	app.add_flag("--no-pace", config.no_pace, "Write frames as fast as possible instead of using recorded timestamps");
+
+	try {
+		app.parse(argc, argv);
+	} catch (const CLI::ParseError &e) {
+		return std::unexpected(app.exit(e));
+	}
+	return config;
+}
+
+[[nodiscard]]
+std::uint64_t proto_timestamp_ns(const google::protobuf::Timestamp &timestamp) {
+	return static_cast<std::uint64_t>(timestamp.seconds()) * 1000000000ull + static_cast<std::uint64_t>(timestamp.nanos());
+}
+
+[[nodiscard]]
+std::expected<std::vector<ReplayMessage>, TesterExitCode> load_messages(const Config &config) {
+	mcap::McapReader reader{};
+	const auto open_status = reader.open(config.input_path);
+	if (!open_status.ok()) {
+		spdlog::error("failed to open MCAP file '{}': {}", config.input_path, open_status.message);
+		return std::unexpected(TesterExitCode::OpenError);
+	}
+
+	std::vector<ReplayMessage> messages{};
+	auto view = reader.readMessages();
+	for (auto it = view.begin(); it != view.end(); ++it) {
+		if (it->schema == nullptr || it->channel == nullptr) {
+			spdlog::error("MCAP message missing schema or channel metadata");
+			reader.close();
+			return std::unexpected(TesterExitCode::SchemaError);
+		}
+		if (it->schema->encoding != "protobuf" || it->schema->name != "foxglove.CompressedVideo") {
+			continue;
+		}
+		if (it->channel->messageEncoding != "protobuf") {
+			spdlog::error("unexpected MCAP message encoding: {}", it->channel->messageEncoding);
+			reader.close();
+			return std::unexpected(TesterExitCode::SchemaError);
+		}
+		if (config.expected_topic && it->channel->topic != *config.expected_topic) {
+			spdlog::error("unexpected topic: expected '{}' got '{}'", *config.expected_topic, it->channel->topic);
+			reader.close();
+			return std::unexpected(TesterExitCode::TopicMismatch);
+		}
+
+		foxglove::CompressedVideo message{};
+		if (!message.ParseFromArray(it->message.data, static_cast<int>(it->message.dataSize))) {
+			spdlog::error("failed to parse foxglove.CompressedVideo payload");
+			reader.close();
+			return std::unexpected(TesterExitCode::ParseError);
+		}
+		if (message.format() != config.expected_format) {
+			spdlog::error("unexpected format: expected '{}' got '{}'", config.expected_format, message.format());
+			reader.close();
+			return std::unexpected(TesterExitCode::FormatMismatch);
+		}
+		if (message.data().empty()) {
+			spdlog::error("compressed video payload is empty");
+			reader.close();
+			return std::unexpected(TesterExitCode::EmptyPayload);
+		}
+
+		auto timestamp_ns = proto_timestamp_ns(message.timestamp());
+		if (timestamp_ns == 0) {
+			timestamp_ns = it->message.logTime;
+		}
+
+		ReplayMessage replay{};
+		replay.timestamp_ns = timestamp_ns;
+		replay.payload.assign(
+			reinterpret_cast<const std::uint8_t *>(message.data().data()),
+			reinterpret_cast<const std::uint8_t *>(message.data().data()) + message.data().size());
+		messages.push_back(std::move(replay));
+	}
+
+	reader.close();
+
+	if (messages.empty()) {
+		spdlog::error("no foxglove.CompressedVideo messages found in '{}'", config.input_path);
+		return std::unexpected(TesterExitCode::EmptyPayload);
+	}
+
+	return messages;
+}
+
+[[nodiscard]]
+const char *ffplay_input_format(std::string_view format) {
+	return format == "h265" ? "hevc" : "h264";
+}
+
+[[nodiscard]]
+std::expected<pid_t, TesterExitCode> spawn_ffplay(
+	const Config &config,
+	int &stdin_write_fd) {
+	int pipe_fds[2]{-1, -1};
+	if (::pipe(pipe_fds) != 0) {
+		spdlog::error("failed to create ffplay stdin pipe: {}", std::strerror(errno));
+		return std::unexpected(TesterExitCode::ProcessError);
+	}
+
+	const auto pid = ::fork();
+	if (pid < 0) {
+		spdlog::error("failed to fork ffplay: {}", std::strerror(errno));
+		::close(pipe_fds[0]);
+		::close(pipe_fds[1]);
+		return std::unexpected(TesterExitCode::ProcessError);
+	}
+
+	if (pid == 0) {
+		::dup2(pipe_fds[0], STDIN_FILENO);
+		::close(pipe_fds[0]);
+		::close(pipe_fds[1]);
+
+		std::vector<std::string> owned_args{};
+		owned_args.push_back(config.ffplay_path);
+		owned_args.push_back("-hide_banner");
+		owned_args.push_back("-loglevel");
+		owned_args.push_back("warning");
+		owned_args.push_back("-fflags");
+		owned_args.push_back("nobuffer");
+		owned_args.push_back("-flags");
+		owned_args.push_back("low_delay");
+		owned_args.push_back("-f");
+		owned_args.push_back(ffplay_input_format(config.expected_format));
+		owned_args.insert(owned_args.end(), config.ffplay_args.begin(), config.ffplay_args.end());
+		owned_args.push_back("pipe:0");
+
+		std::vector<char *> argv{};
+		argv.reserve(owned_args.size() + 1);
+		for (auto &arg : owned_args) {
+			argv.push_back(arg.data());
+		}
+		argv.push_back(nullptr);
+
+		::execvp(config.ffplay_path.c_str(), argv.data());
+		::perror("execvp ffplay");
+		::_exit(127);
+	}
+
+	::close(pipe_fds[0]);
+	stdin_write_fd = pipe_fds[1];
+	return pid;
+}
+
+[[nodiscard]]
+std::expected<void, TesterExitCode> write_all(int fd, std::span<const std::uint8_t> bytes) {
+	std::size_t written{0};
+	while (written < bytes.size()) {
+		const auto result = ::write(fd, bytes.data() + written, bytes.size() - written);
+		if (result < 0) {
+			if (errno == EINTR) {
+				continue;
+			}
+			spdlog::error("failed to write replay data to ffplay: {}", std::strerror(errno));
+			return std::unexpected(TesterExitCode::WriteError);
+		}
+		if (result == 0) {
+			spdlog::error("short write to ffplay stdin");
+			return std::unexpected(TesterExitCode::WriteError);
+		}
+		written += static_cast<std::size_t>(result);
+	}
+	return {};
+}
+
+}
+
+int main(int argc, char **argv) {
+	auto config = parse_args(argc, argv);
+	if (!config) {
+		return config.error();
+	}
+
+	auto messages = load_messages(*config);
+	if (!messages) {
+		return exit_code(messages.error());
+	}
+
+	int stdin_write_fd{-1};
+	auto child_pid = spawn_ffplay(*config, stdin_write_fd);
+	if (!child_pid) {
+		return exit_code(child_pid.error());
+	}
+
+	const auto start_wall = std::chrono::steady_clock::now();
+	const auto first_timestamp = messages->front().timestamp_ns;
+
+	for (const auto &message : *messages) {
+		if (!config->no_pace) {
+			const auto delta_ns = message.timestamp_ns > first_timestamp ? message.timestamp_ns - first_timestamp : 0ull;
+			const auto scaled_ns = static_cast<std::uint64_t>(static_cast<long double>(delta_ns) / config->speed);
+			std::this_thread::sleep_until(start_wall + std::chrono::nanoseconds(scaled_ns));
+		}
+		auto write = write_all(stdin_write_fd, std::span<const std::uint8_t>(message.payload.data(), message.payload.size()));
+		if (!write) {
+			::close(stdin_write_fd);
+			int status = 0;
+			::waitpid(*child_pid, &status, 0);
+			return exit_code(write.error());
+		}
+	}
+
+	::close(stdin_write_fd);
+
+	int status{0};
+	if (::waitpid(*child_pid, &status, 0) < 0) {
+		spdlog::error("failed to wait for ffplay: {}", std::strerror(errno));
+		return exit_code(TesterExitCode::WaitError);
+	}
+	if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
+		spdlog::info("replayed {} MCAP video messages", messages->size());
+		return exit_code(TesterExitCode::Success);
+	}
+	if (WIFSIGNALED(status)) {
+		spdlog::error("ffplay exited on signal {}", WTERMSIG(status));
+		return exit_code(TesterExitCode::WaitError);
+	}
+	if (WIFEXITED(status)) {
+		spdlog::error("ffplay exited with status {}", WEXITSTATUS(status));
+		return WEXITSTATUS(status);
+	}
+	spdlog::error("ffplay exited unexpectedly");
+	return exit_code(TesterExitCode::WaitError);
+}