refactor: VideoReader and videoin cleanup

VideoReader:
- Guard get_source_info/allocate_conversion_buffers behind have_video
  check — prevents crash on audio-only files
- Remove unused audiobuf parameter from get_next_frame
- Remove dead return statements after throw
- Remove unused SourceInfo::stride field and AudioInfo struct
- Pass const std::string& instead of by value in constructor/open_file
- Remove redundant struct keyword on SourceInfo source_info{}
- Fix video_stream_index never guarded against -1 in open_file
- Check av_image_alloc and avcodec_parameters_to_context return values
- Remove extra av_packet_unref after seek (was harmless but confusing)
- Use SWS_BILINEAR for sws_getContext flags instead of 0
- Replace NULL with nullptr in sws_getContext
- Remove unused #include <libavutil/pixdesc.h>

videoin main.cpp:
- Early return if have_video is false after open
- Inline make_video_flow_def call (remove intermediate variable)
- Add grain count log line matching other nodes
- Change continue to break when get_next_frame returns false
- Make video_rate const
- Remove double blank line before main()
- Remove trailing spaces

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nodes/videoin/main.cpp

@@ -4,7 +4,6 @@ extern "C" {
     #include <libavutil/avutil.h>
     #include <libswscale/swscale.h>
     #include <libavutil/imgutils.h>
-    #include <libavutil/pixdesc.h>
 }
 
 #include <string>
@@ -19,51 +18,45 @@ class VideoInNode : public dmf::NodeBase {
     void run() override {
         const std::string filename = config().value("file", std::string{});
         if (filename.empty()) { log("config missing 'file'"); return; }
-        log("VideoIn Node started with file: %s", filename.c_str());
+        log("file: %s", filename.c_str());
+
         dmf::VideoReader video_reader(filename);
+        if (!video_reader.have_video) { log("no video stream found"); return; }
 
         const auto video_flow_info = config().at("video_flow_id");
         const auto video_flow_id   = video_flow_info.at("id").get<std::string>();
-        const int  width           = video_flow_info.value("width",   video_reader.source_info.width);
-        const int  height          = video_flow_info.value("height",  video_reader.source_info.height);
-        const int  fps_num         = video_flow_info.value("fps_num", video_reader.source_info.fps_num);
-        const int  fps_den         = video_flow_info.value("fps_den", video_reader.source_info.fps_den);
+        const int  width    = video_flow_info.value("width",   video_reader.source_info.width);
+        const int  height   = video_flow_info.value("height",  video_reader.source_info.height);
+        const int  fps_num  = video_flow_info.value("fps_num", video_reader.source_info.fps_num);
+        const int  fps_den  = video_flow_info.value("fps_den", video_reader.source_info.fps_den);
 
-        mxlFlowWriter video_writer = nullptr;
-        mxlFlowConfigInfo video_config = {};
-        std::string video_flow_def = dmf::make_video_flow_def(
-            video_flow_id,
-            node_id(),
-            width,
-            height,
-            fps_num,
-            fps_den
-        );
+        log("video flow=%s  %dx%d @ %d/%d fps", video_flow_id.c_str(), width, height, fps_num, fps_den);
+
+        mxlFlowWriter    video_writer = nullptr;
+        mxlFlowConfigInfo video_cfg   = {};
         bool created = false;
         mxlStatus vst = mxlCreateFlowWriter(
             instance(),
-            video_flow_def.c_str(),
-            "",
-            &video_writer,
-            &video_config,
-            &created
-        );
+            dmf::make_video_flow_def(video_flow_id, node_id(), width, height, fps_num, fps_den).c_str(),
+            "", &video_writer, &video_cfg, &created);
         if (vst != MXL_STATUS_OK) {
             log("mxlCreateFlowWriter failed (%s)", dmf::mxl_status_str(vst));
             return;
         }
-        const uint32_t video_stride = video_config.discrete.sliceSizes[0];
+        const uint32_t video_stride = video_cfg.discrete.sliceSizes[0];
+        log("video stride=%u B/line  grain=%u B  ring=%u grains",
+            video_stride, video_stride * static_cast<uint32_t>(height), video_cfg.discrete.grainCount);
 
-        mxlRational video_rate = {fps_num, fps_den};
+        const mxlRational video_rate = {fps_num, fps_den};
         uint64_t video_index = mxlGetCurrentIndex(&video_rate);
 
         while (dmf::g_running.load(std::memory_order_relaxed)) {
-            uint8_t* buf = nullptr;
+            uint8_t*     buf = nullptr;
             mxlGrainInfo grain{};
             vst = mxlFlowWriterOpenGrain(video_writer, video_index, &grain, &buf);
             if (vst == MXL_STATUS_OK) {
-                if (!video_reader.get_next_frame(buf, video_stride, nullptr)) continue;
-                grain.flags = 0;
+                if (!video_reader.get_next_frame(buf, video_stride)) break;
+                grain.flags       = 0;
                 grain.validSlices = grain.totalSlices;
                 mxlFlowWriterCommitGrain(video_writer, &grain);
             }
@@ -72,12 +65,12 @@ class VideoInNode : public dmf::NodeBase {
             video_index++;
         }
 
+        log("stopped at video_index=%llu", video_index);
         mxlReleaseFlowWriter(instance(), video_writer);
     }
 };
 
-
-int main() {    
+int main() {
     VideoInNode node;
     return node.execute();
 }