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server: Enable transcriptions API for LFM2-Audio #22000

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Merged
ngxson merged 1 commit into from
Apr 23, 2026
+43 −14
Merged

server: Enable transcriptions API for LFM2-Audio #22000

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26 changes: 21 additions & 5 deletions common/chat.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -544,6 +544,26 @@ bool common_chat_templates_was_explicit(const struct common_chat_templates * tmp
return tmpls->has_explicit_template;
}

// LFM2 format detection: template uses <|tool_list_start|>[...]<|tool_list_end|> around the tool list
// and <|tool_call_start|>[...]<|tool_call_end|> around each tool call
static bool is_lfm2_template(const std::string & src) {
return src.find("<|tool_list_start|>") != std::string::npos &&
src.find("<|tool_list_end|>") != std::string::npos;
}

common_chat_prompt_preset common_chat_get_asr_prompt(const common_chat_templates * chat_templates) {
common_chat_prompt_preset asr_preset;
asr_preset.system = "";
asr_preset.user = "Transcribe audio to text";

if (chat_templates && chat_templates->template_default && is_lfm2_template(chat_templates->template_default->source())) {
asr_preset.system = "Perform ASR.";
asr_preset.user = "";
}

return asr_preset;
}

std::string common_chat_templates_source(const struct common_chat_templates * tmpls, const std::string & variant) {
if (!variant.empty()) {
if (variant == "tool_use") {
Expand Down Expand Up @@ -2053,10 +2073,7 @@ std::optional<common_chat_params> common_chat_try_specialized_template(
return common_chat_params_init_kimi_k2(tmpl, params);
}

// LFM2 format detection: template uses <|tool_list_start|>[...]<|tool_list_end|> around the tool list
// and <|tool_call_start|>[...]<|tool_call_end|> around each tool call
if (src.find("<|tool_list_start|>") != std::string::npos &&
src.find("<|tool_list_end|>") != std::string::npos) {
if (is_lfm2_template(src)) {
LOG_DBG("Using specialized template: LFM2\n");
return common_chat_params_init_lfm2(tmpl, params);
}
Expand Down Expand Up @@ -2365,4 +2382,3 @@ std::map<std::string, bool> common_chat_templates_get_caps(const common_chat_tem
GGML_ASSERT(chat_templates->template_default != nullptr);
return chat_templates->template_default->caps.to_map();
}

8 changes: 8 additions & 0 deletions common/chat.h
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Original file line number Diff line number Diff line change
Expand Up @@ -274,3 +274,11 @@ std::optional<common_chat_params> common_chat_try_specialized_template(
const common_chat_template & tmpl,
const std::string & src,
autoparser::generation_params & params);

// specialized per-task preset
struct common_chat_prompt_preset {
std::string system;
std::string user;
};

common_chat_prompt_preset common_chat_get_asr_prompt(const common_chat_templates * chat_templates);
21 changes: 12 additions & 9 deletions tools/server/server-chat.cpp
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Expand Up @@ -535,6 +535,7 @@ json server_chat_msg_diff_to_json_oaicompat(const common_chat_msg_diff & diff) {

json convert_transcriptions_to_chatcmpl(
const json & inp_body,
const common_chat_templates * tmpls,
const std::map<std::string, raw_buffer> & in_files,
std::vector<raw_buffer> & out_files) {
// TODO @ngxson : this function may need to be improved in the future
Expand All @@ -548,27 +549,29 @@ json convert_transcriptions_to_chatcmpl(
}

// handle input data
std::string prompt = json_value(inp_body, "prompt", std::string());
std::string language = json_value(inp_body, "language", std::string());
std::string prompt = json_value(inp_body, "prompt", std::string());
std::string language = json_value(inp_body, "language", std::string());
std::string response_format = json_value(inp_body, "response_format", std::string("json"));
if (response_format != "json") {
throw std::invalid_argument("Only 'json' response_format is supported for transcription");
}
const common_chat_prompt_preset preset = common_chat_get_asr_prompt(tmpls);
if (prompt.empty()) {
prompt = "Transcribe audio to text";
prompt = preset.user;
}
if (!language.empty()) {
prompt += string_format(" (language: %s)", language.c_str());
}
prompt += get_media_marker();

json messages = json::array();
if (!preset.system.empty()) {
messages.push_back({{"role", "system"}, {"content", preset.system}});
}
messages.push_back({{"role", "user"}, {"content", prompt}});

json chatcmpl_body = inp_body; // copy all fields
chatcmpl_body["messages"] = json::array({
{
{"role", "user"},
{"content", prompt},
},
});
chatcmpl_body["messages"] = messages;

// because input from form-data, everything is string, we need to correct the types here
std::string stream = json_value(inp_body, "stream", std::string("false"));
Expand Down
1 change: 1 addition & 0 deletions tools/server/server-chat.h
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ json server_chat_convert_anthropic_to_oai(const json & body);
// convert OpenAI transcriptions API format to OpenAI Chat Completions API format
json convert_transcriptions_to_chatcmpl(
const json & body,
const common_chat_templates * tmpls,
const std::map<std::string, raw_buffer> & in_files,
std::vector<raw_buffer> & out_files);

Expand Down
1 change: 1 addition & 0 deletions tools/server/server-context.cpp
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Expand Up @@ -3801,6 +3801,7 @@ void server_routes::init_routes() {
std::vector<raw_buffer> files;
json body = convert_transcriptions_to_chatcmpl(
json::parse(req.body),
meta->chat_params.tmpls.get(),

@ngxson ngxson Apr 17, 2026

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probably better to pass the whole chat_params here instead of just tmpls, that will make this function to be more aligned with oaicompat_chat_params_parse

@pwilkin pwilkin Apr 17, 2026

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Yeah, gonna think about it, probably might be a good idea to unify it and to just pass the entire JSON messages "preset" array.

@ngxson ngxson Apr 20, 2026

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@pwilkin for now I think it should be good to merge, right? If so, can you give an approval? (This can be improved in a follow-up PR if you have any ideas.) Thanks!

@pwilkin pwilkin Apr 21, 2026

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Yes, let's merge it for now.

req.files,
files);
SRV_DBG("%s\n", "Request converted: OpenAI Transcriptions -> OpenAI Chat Completions");
Expand Down
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