Port C(ccx_encoder_srt.c) to Rust(ccxr_encoder_srt.rs)

[VivianVRodrigues]

Overview
This branch migrates the SRT encoder to Rust and refactors the encoder context. 13 files changed: 872 insertions, 101 deletions.
Main Changes

1. New Rust SRT encoder implementation(ccx_encoder_srt rewrite)
   Added src/rust/src/encoder/ccxr_encoder_srt.rs (285 lines)
   Functions: ccxr_write_stringz_srt, ccxr_write_cc_subtitle_as_srt, ccxr_write_cc_buffer_as_srt

2. New encoder context module
   Added src/rust/src/libccxr_exports/encoder_ctx.rs (467 lines)
   Safe Rust wrapper for C encoder_ctx
   Conversion functions: copy_encoder_ctx_c_to_rust, copy_encoder_ctx_rust_to_c
   Rust struct ccxr_encoder_ctx with Vec<ccxr_s_write> for file handles

3. C code integration
   Modified src/lib_ccx/ccx_encoders_srt.c
   Added conditional Rust calls (wrapped in #ifndef DISABLE_RUST)
   Functions delegate to Rust when Rust is enabled:
   write_stringz_as_srt → ccxr_write_stringz_srt
   write_cc_subtitle_as_srt → ccxr_write_cc_subtitle_as_srt
   write_cc_buffer_as_srt → ccxr_write_cc_buffer_as_srt

4. Refactored common encoder utilities to take Rust struct instead of C
   Modified src/rust/src/encoder/common.rs
   Refactored encode_line to take ccxr_encoder_ctx(Rust) instead of encoder_ctx(C)
   Refactored write_subtitle_file_footer_rust to use ccxr_encoder_ctx(Rust) instead of encoder_ctx(C)

5. Build system updates(build related to port )
   Updated src/rust/Cargo.toml and Cargo.lock (new dependencies)
   Updated src/rust/build.rs (build configuration)
   Updated src/rust/wrapper.h (C bindings)
   Updated src/lib_ccx/utility.h (utility declarations)

Local testing on Linux
Test data : https://drive.google.com/drive/folders/1qPm8ImCPg_3nK2kH9aWWWWliqJmwwotR?usp=sharing

[cfsmp3]

Thanks for working on porting the SRT encoder to Rust! However, the build currently fails on Linux.

The issue is in utility.h - you've added function declarations that use struct encoder_ctx, struct cc_subtitle, and struct eia608_screen, but these types aren't visible at that point in the include chain.

To fix this, you have a few options:

1. Add forward declarations at the top of utility.h:

   struct encoder_ctx;
   struct cc_subtitle;
   struct eia608_screen;

2. Or move these declarations to a header that's included after the struct definitions (perhaps ccx_encoders_common.h where encoder_ctx is defined)

Please fix the build and we can continue the review. Thanks!

[VivianVRodrigues]

@carlos Thanks for the review!
Sure I din't consider the warning , but i'll consider henceforth .
I added forward declarations in the utility.h itself , as there could be other files that might include utility.h without ccx_encoders_common.h. If they need these declarations, they’d be missing.

[cfsmp3]

Hi @VivianVRodrigues, thanks for the explanation! Could you push the changes you mentioned so we can verify the build works? The CI needs to run on the updated code to confirm the forward declarations fix the build issue.

[VivianVRodrigues]

Hello @cfsmp3, I have pushed the changes !
It is right before my previous comment.
Thanks .

[cfsmp3]

Closed due to inactivity, feel free to submit a new one (make sure it's based off master) when you are ready to resume work.