VisionEncoderDecoderModel ONNX Conversion - TrOCR
I want to convert my TrOCR model into TFLite version. To do that, based on my understanding, I need to convert it first to ONNX, then to TF, and lastly to TFLite. I stumbled upon [#19604](https://github.com/huggingface/transformers/pull/19254). However, it's a bit different. In my case, I used the `trainer.save` function to save my finetuned TrOCR model. As a result, I got the checkpoint files and also these files:
```
config.json
generation_config.json
preprocessor_config.json
pytorch_model.bin
training_args.bin
```

Command I used:
```
python -m transformers.onnx --model=trocr/base/ --feature=vision2seq-lm onnx/ --atol 1e-3
```

Error that I still got:
```
ValueError: Unrecognized feature extractor in base/. Should have a `feature_extractor_type` key in its preprocessor_config.json of config.json, or one of the following `model_type` keys in its config.json: audio-spectrogram-transformer, beit, chinese_clip, clap, clip, clipseg, conditional_detr, convnext, cvt, data2vec-audio, data2vec-vision, deformable_detr, deit, detr, dinat, donut-swin, dpt, flava, glpn, groupvit, hubert, imagegpt, layoutlmv2, layoutlmv3, levit, maskformer, mctct, mobilenet_v1, mobilenet_v2, mobilevit, nat, owlvit, perceiver, poolformer, regnet, resnet, segformer, sew, sew-d, speech_to_text, speecht5, swin, swinv2, table-transformer, timesformer, tvlt, unispeech, unispeech-sat, van, videomae, vilt, vit, vit_mae, vit_msn, wav2vec2, wav2vec2-conformer, wavlm, whisper, xclip, yolos
```

In the `config.json`, I have both `trocr` and `vision-encoder-decoder` as the model type, which is not included in the list given by the  error. Any other way to do this?
cc @Rocketknight1  maybe?<|||||>@sgugger pinging since there's no response<|||||>It looks like this bug is arising in ONNX export of a PyTorch model, which I don't know too much about!<|||||>I'm quite confused on this one. Any other workarounds on this? I did read some ways like JIT or using the export function of Torch, but not quite sure on how to do it, especially the input part.<|||||>Would need help referring this issue to others @Rocketknight1 @sgugger, appreciate it! :D<|||||>@sgugger @Rocketknight1 I'm also facing this same issue. Any help would be much appreciated. Thanks! <|||||>@NielsRogge @michaelbenayoun <|||||>Hi,
Could you try with [Optimum](https://github.com/huggingface/optimum)?

```
optimum-cli export onnx  -m trocr/base/ --task vision2seq-lm onnx/ --atol 1e-3
```
Trying to pinpoint if it comes from the exporting tool or really from some information lacking in the `preprocessor_config.json` file.<|||||>Hi @michaelbenayoun, thank you for the response. Yes, I retried using Optimum and it works. I then continued my conversion to TF and TFLite with these commands.

```
optimum-cli export onnx --model base/ onnx/ --task vision2seq-lm

onnx-tf convert -i onnx/encoder_model.onnx -o encoder/
onnx-tf convert -i onnx/decoder_model.onnx -o decoder/

tflite_convert --saved_model_dir=encoder/ --output_file=encoder.tflite
tflite_convert --saved_model_dir=decoder/ --output_file=decoder.tflite
```

When I check the encoder input shape to use it for inference, I got the following:
```
[{'name': 'serving_default_pixel_values:0',
  'index': 0,
  'shape': array([1, 1, 1, 1], dtype=int32),
  'shape_signature': array([-1, -1, -1, -1], dtype=int32),
  'dtype': numpy.float32,
  'quantization': (0.0, 0),
  'quantization_parameters': {'scales': array([], dtype=float32),
   'zero_points': array([], dtype=int32),
   'quantized_dimension': 0},
  'sparsity_parameters': {}}]
```

Any idea on how to fix this? It can't be the correct expected shape right?<|||||>We support also the export to TFLIte directly in Optimum, but not for TrOCR yet, just letting you know.

About your issue, if I understand correctly you convert the ONNX models to a TensorFlow SavedModels. 

Once you have done that, I would suggest convert those SavedModels to TFLite programatically, for each SavedModel try:

1. Load the SavedModel
2. Create a `tf.function` with the proper input signature from it: 
```python
func = tf.function(loaded_model, input_signature=[tf.TensorSpec([shape here], dtype=torch.float32)])
```
4. Create a concrete function from `func`:
```python
concrete_func = func.get_concrete_function()
```
5. Convert the concrete function to TFLite following this [example](https://www.tensorflow.org/lite/models/convert/convert_models?hl=fr#convert_concrete_functions_)

Tell me if it works!<|||||>Wow, thank you for the heads-up @michaelbenayoun, that Optimum feature is surely awaited! 

Anyway, I tried your suggestion. Currently:
```
model = tf.saved_model.load("converted/tf/encoder/")
func = tf.function(model, input_signature=[tf.TensorSpec([1, 384, 384, 3], dtype=tf.float32)])
concrete_func = func.get_concrete_function()
```

However, I got this error from the concrete function getter:
```
 ValueError: Could not find matching concrete function to call loaded from the SavedModel. Got:
      Positional arguments (1 total):
        * <tf.Tensor 'None_0:0' shape=(1, 384, 384, 3) dtype=float32>
      Keyword arguments: {}
    
     Expected these arguments to match one of the following 1 option(s):
    
    Option 1:
      Positional arguments (0 total):
        * 
      Keyword arguments: {'pixel_values': TensorSpec(shape=(None, None, None, None), dtype=tf.float32, name='pixel_values')}
```

From my research I think this is because the shape is incorrect, but I don't know how to reshape the input. Any other suggestion on this? TIA! :D<|||||>I think it's because it does not recognize the input signature. 

Could you try:
```python
func = tf.function(model, input_signature=[tf.TensorSpec([1, 384, 384, 3], dtype=tf.float32, name="pixel_values")])
```<|||||>Nope, still got the same error with that. <|||||>any updates on this,
I am also facing this issue @RichardRivaldo @michaelbenayoun <|||||>no @textyash20 have you found the solution for this?<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.