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Add -o/--output flag to write transcription text to a file #113

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370d79c
add -o/--output flag to write transcription text to a file
tim-janik Jul 25, 2026
19be2a1
tweaks
cjpais Jul 30, 2026
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58 changes: 49 additions & 9 deletions examples/cli/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -204,13 +204,14 @@ struct cli_args {
bool quiet = false;
bool list_devices = false; // --list-devices: print devices and exit
bool batch_jsonl = false; // --batch-jsonl: output JSONL
int repeat = 1;
int n_threads = 0; // 0 = library default (all cores)
int n_ctx = 0; // 0 = model's true max; >0 lowers the cap
transcribe_kv_type kv_type = TRANSCRIBE_KV_TYPE_AUTO;
transcribe_backend_request backend = TRANSCRIBE_BACKEND_AUTO;
int gpu_device = 0; // --device N: 0 = auto, >0 = registry index
transcribe_timestamp_kind timestamps = TRANSCRIBE_TIMESTAMPS_AUTO;
std::string output_path; // -o/--output: write raw text here
int repeat = 1;
int n_threads = 0; // 0 = library default (all cores)
int n_ctx = 0; // 0 = model's true max; >0 lowers the cap
transcribe_kv_type kv_type = TRANSCRIBE_KV_TYPE_AUTO;
transcribe_backend_request backend = TRANSCRIBE_BACKEND_AUTO;
int gpu_device = 0; // --device N: 0 = auto, >0 = registry index
transcribe_timestamp_kind timestamps = TRANSCRIBE_TIMESTAMPS_AUTO;

// Whisper-family knobs. Ignored for non-Whisper models.
std::string initial_prompt; // --initial-prompt TEXT
Expand Down Expand Up @@ -282,6 +283,7 @@ void print_usage(const char * argv0) {
" --target-language ISO target language for translation (e.g. de, es, fr)\n"
" -q, --quiet suppress library log output\n"
" -r, --repeat N run N times per file (benchmark)\n"
" -o, --output PATH write transcribed text to PATH (stdout unchanged)\n"
" --threads N CPU threads (default: all cores)\n"
" --n-ctx N session context/KV cap in tokens (bounds decoder\n"
" KV memory; cannot extend the model): 0 = model\n"
Expand Down Expand Up @@ -528,6 +530,12 @@ bool parse_args(int argc, char ** argv, cli_args & out) {
std::fprintf(stderr, "error: --batch-size must be >= 0\n");
return false;
}
} else if (a == "-o" || a == "--output") {
const char * v = take_value(a.c_str());
if (!v) {
return false;
}
out.output_path = v;
} else if (a == "--initial-prompt") {
const char * v = take_value(a.c_str());
if (!v) {
Expand Down Expand Up @@ -688,6 +696,23 @@ void log_cb(transcribe_log_level level, const char * msg, void * userdata) {
std::fprintf(stderr, "%s %s%s", prefix, msg, (msg && *msg && msg[std::strlen(msg) - 1] == '\n') ? "" : "\n");
}

bool write_output_file(std::ofstream * output, const std::string & path, const char * text) {
if (output == nullptr) {
return true;
}
const char * value = text != nullptr ? text : "";
*output << value;
if (value[0] == '\0' || value[std::strlen(value) - 1] != '\n') {
*output << '\n';
}
output->flush();
if (!*output) {
std::fprintf(stderr, "error: cannot write %s\n", path.c_str());
return false;
}
return true;
}

} // namespace

int main(int argc, char ** argv) {
Expand All @@ -713,6 +738,18 @@ int main(int argc, char ** argv) {
transcribe_log_set(log_cb, nullptr);
}

std::ofstream output_file;
std::ofstream * output = nullptr;
if (!args.output_path.empty()) {
output_file.open(args.output_path, std::ios::binary | std::ios::trunc);
if (!output_file) {
std::fprintf(stderr, "error: cannot open %s for writing\n", args.output_path.c_str());
return EXIT_FAILURE;
}
output = &output_file;
}
bool output_ok = true;

// Batch mode: --batch reads a file list, one wav path per line. Loads
// the model ONCE and reuses the context across all files. Outputs one
// JSONL line per file to stdout when --batch-jsonl is set, otherwise
Expand Down Expand Up @@ -957,6 +994,7 @@ int main(int argc, char ** argv) {
std::printf(" ERROR: %s\n", transcribe_status_string(ust));
}
}
output_ok = write_output_file(output, args.output_path, text) && output_ok;
std::fflush(stdout);
}
}
Expand Down Expand Up @@ -1095,6 +1133,7 @@ int main(int argc, char ** argv) {
std::printf(" ERROR: %s\n", transcribe_status_string(run_st));
}
}
output_ok = write_output_file(output, args.output_path, text) && output_ok;
std::fflush(stdout);
}
}
Expand All @@ -1108,7 +1147,7 @@ int main(int argc, char ** argv) {
transcribe_model_free(model);
// OUTPUT_TRUNCATED is result-bearing and does not fail the batch, but
// hard per-utterance failures must remain visible to automation.
return n_fail > 0 ? EXIT_FAILURE : EXIT_SUCCESS;
return n_fail > 0 || !output_ok ? EXIT_FAILURE : EXIT_SUCCESS;
}

// Single-file mode.
Expand Down Expand Up @@ -1341,6 +1380,7 @@ int main(int argc, char ** argv) {
if (result_present) {
const char * text = transcribe_full_text(ctx);
std::printf("text: %s\n", (text && *text) ? text : "(empty)");
output_ok = write_output_file(output, args.output_path, text) && output_ok;

// A truncated decode hit the model's context/output budget before
// end-of-stream; the text above is incomplete.
Expand Down Expand Up @@ -1418,7 +1458,7 @@ int main(int argc, char ** argv) {
transcribe_session_free(ctx);
transcribe_model_free(model);

if (run_st != TRANSCRIBE_OK) {
if (run_st != TRANSCRIBE_OK || !output_ok) {
return EXIT_FAILURE;
}
} else {
Expand Down
7 changes: 7 additions & 0 deletions tests/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -1234,4 +1234,11 @@ if(TRANSCRIBE_BUILD_EXAMPLES)
${CMAKE_SOURCE_DIR}/samples/jfk.wav)
set_tests_properties(transcribe_cli_smoke PROPERTIES
PASS_REGULAR_EXPRESSION "duration:")

add_test(NAME transcribe_cli_output_smoke
COMMAND ${CMAKE_COMMAND}
-DCLI=$<TARGET_FILE:transcribe-cli>
-DWAV=${CMAKE_SOURCE_DIR}/samples/jfk.wav
-DTEST_DIR=${CMAKE_CURRENT_BINARY_DIR}/cli-output-smoke
-P ${CMAKE_CURRENT_SOURCE_DIR}/cli_output_smoke.cmake)
endif()
36 changes: 36 additions & 0 deletions tests/cli_output_smoke.cmake
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Original file line number Diff line number Diff line change
@@ -0,0 +1,36 @@
foreach(_var CLI WAV TEST_DIR)
if(NOT DEFINED ${_var} OR "${${_var}}" STREQUAL "")
message(FATAL_ERROR "${_var} is required")
endif()
endforeach()

file(REMOVE_RECURSE "${TEST_DIR}")
file(MAKE_DIRECTORY "${TEST_DIR}")

set(_output "${TEST_DIR}/transcript.txt")
file(WRITE "${_output}" "stale output\n")
execute_process(
COMMAND "${CLI}" -q -o "${_output}" "${WAV}"
RESULT_VARIABLE _result
OUTPUT_VARIABLE _stdout
ERROR_VARIABLE _stderr)
if(NOT _result EQUAL 0)
message(FATAL_ERROR "output command failed (${_result}):\n${_stdout}\n${_stderr}")
endif()
file(SIZE "${_output}" _output_size)
if(NOT _output_size EQUAL 0)
message(FATAL_ERROR "--output did not truncate stale output")
endif()

set(_bad_output "${TEST_DIR}/missing/transcript.txt")
execute_process(
COMMAND "${CLI}" -q -o "${_bad_output}" "${WAV}"
RESULT_VARIABLE _bad_result
OUTPUT_VARIABLE _bad_stdout
ERROR_VARIABLE _bad_stderr)
if(_bad_result EQUAL 0)
message(FATAL_ERROR "unwritable output path unexpectedly succeeded")
endif()
if(EXISTS "${_bad_output}")
message(FATAL_ERROR "unwritable output path unexpectedly created a file")
endif()