refactor: remove dead FfmpegCamera::imagePixFormat field

The field was assigned in three branches of the constructor (always to
the same value as Camera::pixelFormat) and never read anywhere. Unlike
LocalCamera, FfmpegCamera doesn't run a sws_scale step at the Camera
layer — libavcodec hands frames to the pipeline directly — so there's
no separate capture-vs-image format distinction to track.

Drop the redundant assignments and the member declaration. The
canonical camera-side format is now exclusively Camera::pixelFormat
(via Camera::PixelFormat()).

refs #4788

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/zm_ffmpeg_camera.cpp

@@ -96,15 +96,12 @@ FfmpegCamera::FfmpegCamera(
    * will receive correct colours and subpixel order */
   if ( zm_is_rgb32(pixelFormat) ) {
     subpixelorder = ZM_SUBPIX_ORDER_RGBA;
-    imagePixFormat = AV_PIX_FMT_RGBA;
     pixelFormat = AV_PIX_FMT_RGBA;
   } else if ( zm_is_rgb24(pixelFormat) ) {
     subpixelorder = ZM_SUBPIX_ORDER_RGB;
-    imagePixFormat = AV_PIX_FMT_RGB24;
     pixelFormat = AV_PIX_FMT_RGB24;
   } else if ( pixelFormat == AV_PIX_FMT_GRAY8 ) {
     subpixelorder = ZM_SUBPIX_ORDER_NONE;
-    imagePixFormat = AV_PIX_FMT_GRAY8;
     pixelFormat = AV_PIX_FMT_GRAY8;
   } else {
     Panic("Unexpected pixel format %d (%s); legacy colours=%d subpixelorder=%d",

src/zm_ffmpeg_camera.h

@@ -54,8 +54,6 @@ class FfmpegCamera : public Camera {
 
   int frameCount;
 
-  _AVPIXELFORMAT      imagePixFormat;
-
   bool                use_hwaccel; //will default to on if hwaccel specified, will get turned off if there is a failure
 #if HAVE_LIBAVUTIL_HWCONTEXT_H
   AVBufferRef *hw_device_ctx = nullptr;