app: route all FFmpeg access through the ffmpeg_bridge C API

Replace every direct FFmpeg call in the editor and the render worker
with the pure C ffmpeg_bridge API, wrapped in thin C++ adapters that
preserve the original interfaces:

- avframeptr.h: olive::AVFrame adapter around FBFrame handles
- ffmpegutils: format conversion helpers on FB_* constants; the int
  overload is renamed GetCompatibleBridgePixelFormat to avoid a silent
  overload-resolution trap with the PixelFormat enum
- ffmpegdecoder/ffmpegencoder: rewritten as handle-based adapters over
  FBDecoder/FBProbe/FBEncoder/FBScaler/FBResampler
- audioprocessor: FBAudioGraph push/pull adapter
- pluginrenderer/OliveClip: sws/pixdesc usage converted to FBScaler and
  fb_pix_fmt_* queries
- AudioParams/channel layouts are plain uint64_t masks everywhere

Build integration: the root project no longer links FFMPEG directly;
only ffmpeg_bridge does. Binaries resolve the bridge library at runtime
via @loader_path inside the macOS app bundle (copied there post-build)
and via $ORIGIN/../ffmpeg_bridge/bin on Linux; on Windows the DLL is
installed next to the executables, so packages on all three platforms
ship the bridge library.

ffmpeg_bridge gains the extra API the adapters need:
fb_frame_make_writable, fb_decoder_get_format_duration,
fb_resampler_convert_frame, FB_PIX_FMT_YUV440P, SRT validation in
fb_probe_read_subtitle_stream, packed/planar fixes in
fb_encoder_write_audio, and a component-size fix in
fb_pix_fmt_component_size.

app/codec/ffmpeg/ffmpegencoder.h

@@ -22,19 +22,20 @@
 #ifndef FFMPEGENCODER_H
 #define FFMPEGENCODER_H
 
-extern "C" {
-#include <libavcodec/avcodec.h>
-#include <libavfilter/avfilter.h>
-#include <libavformat/avformat.h>
-#include <libswresample/swresample.h>
-#include <libavutil/opt.h>
-}
+#include <ffmpeg_bridge/ffmpeg_bridge.h>
 
 #include "codec/encoder.h"
 
 namespace olive
 {
 
+/**
+ * @brief An Encoder derivative that uses the ffmpeg_bridge library for encoding
+ *
+ * All encoding work happens inside the ffmpeg_bridge shared library through
+ * its pure C API; this class only translates EncodingParams into a bridge
+ * configuration and forwards calls.
+ */
 class FFmpegEncoder : public Encoder {
 	Q_OBJECT
 public:
@@ -67,54 +68,16 @@ public:
 
 private:
 	/**
-   * @brief Handle an FFmpeg error code
-   *
-   * Uses the FFmpeg API to retrieve a descriptive string for this error code and sends it to Error(). As such, this
-   * function also automatically closes the Decoder.
-   *
-   * @param error_code
+   * @brief Copy the last error message from the bridge into the encoder error state
    */
-	void FFmpegError(const QString &context, int error_code);
+	void SetErrorFromBridge();
 
-	bool WriteAVFrame(AVFrame *frame, AVCodecContext *codec_ctx,
-					  AVStream *stream);
+	static int ExportCodecToBridge(ExportCodec::Codec c);
 
-	bool InitializeStream(enum AVMediaType type, AVStream **stream,
-						  AVCodecContext **codec_ctx,
-						  const ExportCodec::Codec &codec);
-	bool InitializeCodecContext(AVStream **stream, AVCodecContext **codec_ctx,
-								const AVCodec *codec);
-	bool SetupCodecContext(AVStream *stream, AVCodecContext *codec_ctx,
-						   const AVCodec *codec);
+	FBEncoder *encoder_;
 
-	void FlushEncoders();
-	void FlushCodecCtx(AVCodecContext *codec_ctx, AVStream *stream);
-
-	bool InitializeResampleContext(const AudioParams &audio);
-
-	static const AVCodec *GetEncoder(ExportCodec::Codec c,
-									 SampleFormat aformat);
-
-	AVFormatContext *fmt_ctx_;
-
-	AVStream *video_stream_;
-	AVCodecContext *video_codec_ctx_;
-	AVFilterGraph *video_scale_ctx_;
-	AVFilterContext *video_buffersrc_ctx_;
-	AVFilterContext *video_buffersink_ctx_;
 	PixelFormat video_conversion_fmt_;
 
-	AVStream *audio_stream_;
-	AVCodecContext *audio_codec_ctx_;
-	SwrContext *audio_resample_ctx_;
-	AVFrame *audio_frame_;
-	int audio_max_samples_;
-	int audio_frame_offset_;
-	int audio_write_count_;
-
-	AVStream *subtitle_stream_;
-	AVCodecContext *subtitle_codec_ctx_;
-
 	bool open_;
 };