mtmd: support pocket-tts (#26871)

* adapt the api

* text model ok

* working impl, need verify and clean up

* mtmd: build the pocket-tts transposed convolutions as GEMM + col2im

ggml_conv_transpose_1d has no grouped mode, so the depthwise upsample
was built as one convolution and one concat per channel, which floods
the graph with small nodes and makes kernel launches dominate the
decoder.

Fold both cases into the column form the seanet decoder already needs:
the general case reshapes the kernel to [IC, K * OC] and matmuls it
with the input, the depthwise case batches a matmul over the channels
so a step scales its own kernel. A single col2im_1d then scatter-adds
the columns back to the signal, with the same shape as before, so the
overlap-add tail, the streaming state and the bias are untouched.

Generation time per frame drops by 80% on CUDA and by 50% on CPU. The
output matches the previous implementation sample for sample, with a
correlation of 0.999994 and identical frame counts.

* flow_temp +  frames_after_eos

* chunking

* mtmd: carry the remaining pocket-tts per-pack settings

The language packs also tune the end-of-speech padding and the padding
of short prompts, next to the temperature already carried in the
mmproj: french_24l asks for 8 tail frames instead of the guessed 3,
english_2026-01 asks for short prompts to be padded with spaces.

Write both in the mmproj as clip.gen.audio.frames_after_eos and
clip.gen.audio.pad_short_text, keyed on the pack in the conversion
script like the temperature. The loader keeps them optional, so a
mmproj without them behaves as before. Map semicolons to commas for
every pack instead, the reference only asks for it on three of them and
it costs nothing elsewhere.

Existing mmproj files must be converted again to carry the two keys.

On a long french text the port now lands within 2% of the reference:
22.96s against 23.44s, with the same peak level and the same amount of
silence.

* clip.gen.audio.model_variant

* clean up code comments

* nit: drop the dead flow_temp hparam, the pack table holds the default

* update docs

* address security problems

* less invasive base.py

* lint

* add mtmd_gen_inp_default

* add docs

* rm gen_flow_temp

---------

Co-authored-by: Pascal <admin@serveurperso.com>

tools/mtmd/mtmd-helper.h

@@ -183,8 +183,9 @@ struct mtmd_helper_gen_audio_inp {
     mtmd_bitmap * speaker_ref; // optional, can be NULL
     const char * lang; // optional, can be NULL
 
-    int32_t top_k;
-    float   top_p;
+    int32_t  top_k;
+    float    top_p;
+    uint32_t seed; // UINT32_MAX for random (default: random)
 
     enum mtmd_helper_gen_audio_outtype out_type;
 };
@@ -208,12 +209,15 @@ MTMD_API int32_t mtmd_helper_gen_audio_step_prompt(
                         int32_t n_batch);
 
 // generates one frame; must only be called after step_prompt() has returned 0
-// h_state_out is valid until next step_gen() or reset() call
+// sampled can be LLAMA_TOKEN_NULL for pipelines with no discrete backbone token
+// out_stop (optional) is set on end-of-speech, the caller must then stop the loop
+// h_state_out is valid until next step_gen() or reset() call, null if no frame is generated
 MTMD_API int32_t mtmd_helper_gen_audio_step_gen(
                         mtmd_helper_gen_audio * ctx,
                         llama_token sampled,
                         const float *  h_state_in,
-                        const float ** h_state_out);
+                        const float ** h_state_out,
+                        bool * out_stop);
 
 // out_data valid until next get_output() or reset() call
 // out_n_samples (optional, can be NULL) receives the number of generated PCM samples
@@ -261,8 +265,8 @@ struct gen_audio {
     int32_t step_prompt(int32_t n_batch) {
         return mtmd_helper_gen_audio_step_prompt(ctx.get(), n_batch);
     }
-    int32_t step_gen(llama_token sampled, const float * h_state, const float ** h_state_out) {
-        return mtmd_helper_gen_audio_step_gen(ctx.get(), sampled, h_state, h_state_out);
+    int32_t step_gen(llama_token sampled, const float * h_state, const float ** h_state_out, bool * out_stop = nullptr) {
+        return mtmd_helper_gen_audio_step_gen(ctx.get(), sampled, h_state, h_state_out, out_stop);
     }
     int32_t get_output(int32_t * out_sample_rate, const char ** out_data, size_t * out_data_len, int64_t * out_n_samples = nullptr) {
         return mtmd_helper_gen_audio_get_output(ctx.get(), out_sample_rate, out_data, out_data_len, out_n_samples);