Improve error messaging when VAAPI/VDPAU pixel format selection fails.

diff --git a/nageru/ffmpeg_capture.cpp b/nageru/ffmpeg_capture.cpp
index 0dea5598555921c401d8e3d463796dc3edaad9f6..863f4fba4feaecc40b14d07b4662a04740c1894c 100644 (file)
--- a/nageru/ffmpeg_capture.cpp
+++ b/nageru/ffmpeg_capture.cpp
@@ -26,6 +26,7 @@ extern "C" {
 #include <cstdint>
 #include <utility>
 #include <vector>
+#include <unordered_set>
 
 #include <Eigen/Core>
 #include <Eigen/LU>
@@ -457,19 +458,44 @@ void FFmpegCapture::send_disconnected_frame()
 template<AVHWDeviceType type>
 AVPixelFormat get_hw_format(AVCodecContext *ctx, const AVPixelFormat *fmt)
 {
-       for (const AVPixelFormat *fmt_ptr = fmt; *fmt_ptr != -1; ++fmt_ptr) {
-               for (int i = 0;; ++i) {  // Termination condition inside loop.
-                       const AVCodecHWConfig *config = avcodec_get_hw_config(ctx->codec, i);
-                       if (config == nullptr) {  // End of list.
-                               fprintf(stderr, "Decoder %s does not support device.\n", ctx->codec->name);
-                               break;
-                       }
-                       if (config->methods & AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE_CTX &&
-                           config->device_type == type &&
-                           config->pix_fmt == *fmt_ptr) {
+       bool found_config_of_right_type = false;
+       for (int i = 0;; ++i) {  // Termination condition inside loop.
+               const AVCodecHWConfig *config = avcodec_get_hw_config(ctx->codec, i);
+               if (config == nullptr) {  // End of list.
+                       break;
+               }
+               if (!(config->methods & AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE_CTX) ||
+                   config->device_type != type) {
+                       // Not interesting for us.
+                       continue;
+               }
+
+               // We have a config of the right type, but does it actually support
+               // the pixel format we want? (Seemingly, FFmpeg's way of signaling errors
+               // is to just replace the pixel format with a software-decoded one,
+               // such as yuv420p.)
+               found_config_of_right_type = true;
+               for (const AVPixelFormat *fmt_ptr = fmt; *fmt_ptr != -1; ++fmt_ptr) {
+                       if (config->pix_fmt == *fmt_ptr) {
+                               fprintf(stderr, "Initialized '%s' hardware decoding for codec '%s'.\n",
+                                       av_hwdevice_get_type_name(type), ctx->codec->name);
                                return config->pix_fmt;
                        }
                }
+               fprintf(stderr, "Decoder '%s' supports only these pixel formats:", ctx->codec->name);
+               unordered_set<AVPixelFormat> seen;
+               for (const AVPixelFormat *fmt_ptr = fmt; *fmt_ptr != -1; ++fmt_ptr) {
+                       if (!seen.count(*fmt_ptr)) {
+                               fprintf(stderr, " %s", av_get_pix_fmt_name(*fmt_ptr));
+                               seen.insert(*fmt_ptr);
+                       }
+               }
+               fprintf(stderr, " (wanted %s for hardware acceleration)\n", av_get_pix_fmt_name(config->pix_fmt));
+
+       }
+
+       if (!found_config_of_right_type) {
+               fprintf(stderr, "Decoder '%s' does not support device type '%s'.\n", ctx->codec->name, av_hwdevice_get_type_name(type));
        }
 
        // We found no VA-API formats, so take the best software format.