Enable loudnorm filter in smoke builds and harden its impl

test_streams.py::test_loudnorm calls av.filter.loudnorm, so add loudnorm
to the trimmed smoke-build filter list; without it the filter lookup
returned NULL.

That NULL also exposed a crash: loudnorm_get_stats() built an
abuffer -> loudnorm -> abuffersink graph but ignored every return code,
so a NULL loudnorm context was passed to avfilter_link() and segfaulted
the interpreter. Bail out early if a required filter is missing, check
the create_filter/link/graph_config return codes so a NULL context can
never be linked, free the graph on the error path, and skip the 5s JSON
wait when no graph ran. On failure the function returns NULL, which the
Python wrapper already turns into a RuntimeError.

Author: WyattBlue

av/filter/loudnorm_impl.c

@@ -57,6 +57,20 @@ char* loudnorm_get_stats(
     const char* loudnorm_args
 ) {
     char* result = NULL;
+
+    // Bail out cleanly if FFmpeg was built without a filter we depend on,
+    // instead of dereferencing a NULL filter context further down. The caller
+    // turns a NULL return into a Python exception.
+    if (!avfilter_get_by_name("abuffer") ||
+        !avfilter_get_by_name("abuffersink") ||
+        !avfilter_get_by_name("loudnorm")) {
+        av_log(NULL, AV_LOG_ERROR,
+            "loudnorm: a required filter (abuffer/abuffersink/loudnorm) is not "
+            "available in this FFmpeg build\n");
+        avformat_close_input(&fmt_ctx);
+        return NULL;
+    }
+
     json_captured = 0;    // Reset the captured flag
     memset(json_buffer, 0, sizeof(json_buffer));  // Clear the buffer
 
@@ -76,7 +90,10 @@ char* loudnorm_get_stats(
 
     AVCodec *codec = NULL;
     AVCodecContext *codec_ctx = NULL;
+    AVPacket *packet = NULL;
+    AVFrame *frame = NULL, *filt_frame = NULL;
     int ret;
+    int graph_configured = 0;
 
     AVCodecParameters *codecpar = fmt_ctx->streams[audio_stream_index]->codecpar;
     codec = (AVCodec *)avcodec_find_decoder(codecpar->codec_id);
@@ -98,20 +115,25 @@ char* loudnorm_get_stats(
         av_get_sample_fmt_name(codec_ctx->sample_fmt),
         ch_layout_str);
 
-    avfilter_graph_create_filter(&src_ctx, avfilter_get_by_name("abuffer"),
-        "src", args, NULL, filter_graph);
-    avfilter_graph_create_filter(&sink_ctx, avfilter_get_by_name("abuffersink"),
-        "sink", NULL, NULL, filter_graph);
-    avfilter_graph_create_filter(&loudnorm_ctx, avfilter_get_by_name("loudnorm"),
-        "loudnorm", loudnorm_args, NULL, filter_graph);
+    if (avfilter_graph_create_filter(&src_ctx, avfilter_get_by_name("abuffer"),
+            "src", args, NULL, filter_graph) < 0 ||
+        avfilter_graph_create_filter(&sink_ctx, avfilter_get_by_name("abuffersink"),
+            "sink", NULL, NULL, filter_graph) < 0 ||
+        avfilter_graph_create_filter(&loudnorm_ctx, avfilter_get_by_name("loudnorm"),
+            "loudnorm", loudnorm_args, NULL, filter_graph) < 0) {
+        goto end;
+    }
 
-    avfilter_link(src_ctx, 0, loudnorm_ctx, 0);
-    avfilter_link(loudnorm_ctx, 0, sink_ctx, 0);
-    avfilter_graph_config(filter_graph, NULL);
+    if (avfilter_link(src_ctx, 0, loudnorm_ctx, 0) < 0 ||
+        avfilter_link(loudnorm_ctx, 0, sink_ctx, 0) < 0 ||
+        avfilter_graph_config(filter_graph, NULL) < 0) {
+        goto end;
+    }
+    graph_configured = 1;
 
-    AVPacket *packet = av_packet_alloc();
-    AVFrame *frame = av_frame_alloc();
-    AVFrame *filt_frame = av_frame_alloc();
+    packet = av_packet_alloc();
+    frame = av_frame_alloc();
+    filt_frame = av_frame_alloc();
 
     while ((ret = av_read_frame(fmt_ctx, packet)) >= 0) {
         if (packet->stream_index != audio_stream_index) {
@@ -157,46 +179,50 @@ char* loudnorm_get_stats(
         av_frame_unref(filt_frame);
     }
 
-    // Pushes graph
-    avfilter_graph_free(&filter_graph);
-
 end:
+    // Freeing the graph uninits the loudnorm filter, which is what makes it
+    // emit its JSON stats through our log callback. Safe to call on NULL.
+    avfilter_graph_free(&filter_graph);
     avcodec_free_context(&codec_ctx);
     avformat_close_input(&fmt_ctx);
     av_frame_free(&filt_frame);
     av_frame_free(&frame);
     av_packet_free(&packet);
 
-    #ifdef _WIN32
-    EnterCriticalSection(&json_mutex);
-    while (!json_captured) {
-        if (!SleepConditionVariableCS(&json_cond, &json_mutex, 5000)) { // 5 second timeout
-            fprintf(stderr, "Timeout waiting for JSON data\n");
-            break;
+    // If the graph never configured we produced no stats; don't block waiting
+    // for JSON that will never arrive. Leave result NULL so the caller raises.
+    if (graph_configured) {
+        #ifdef _WIN32
+        EnterCriticalSection(&json_mutex);
+        while (!json_captured) {
+            if (!SleepConditionVariableCS(&json_cond, &json_mutex, 5000)) { // 5 second timeout
+                fprintf(stderr, "Timeout waiting for JSON data\n");
+                break;
+            }
         }
-    }
-    if (json_captured) {
-        result = _strdup(json_buffer);  // Use _strdup on Windows
-    }
-    LeaveCriticalSection(&json_mutex);
-    #else
-    struct timespec timeout;
-    clock_gettime(CLOCK_REALTIME, &timeout);
-    timeout.tv_sec += 5;  // 5 second timeout
-
-    pthread_mutex_lock(&json_mutex);
-    while (json_captured == 0) {
-        int ret = pthread_cond_timedwait(&json_cond, &json_mutex, &timeout);
-        if (ret == ETIMEDOUT) {
-            fprintf(stderr, "Timeout waiting for JSON data\n");
-            break;
+        if (json_captured) {
+            result = _strdup(json_buffer);  // Use _strdup on Windows
         }
+        LeaveCriticalSection(&json_mutex);
+        #else
+        struct timespec timeout;
+        clock_gettime(CLOCK_REALTIME, &timeout);
+        timeout.tv_sec += 5;  // 5 second timeout
+
+        pthread_mutex_lock(&json_mutex);
+        while (json_captured == 0) {
+            int ret = pthread_cond_timedwait(&json_cond, &json_mutex, &timeout);
+            if (ret == ETIMEDOUT) {
+                fprintf(stderr, "Timeout waiting for JSON data\n");
+                break;
+            }
+        }
+        if (json_captured) {
+            result = strdup(json_buffer);
+        }
+        pthread_mutex_unlock(&json_mutex);
+        #endif
     }
-    if (json_captured) {
-        result = strdup(json_buffer);
-    }
-    pthread_mutex_unlock(&json_mutex);
-    #endif
 
     av_log_set_callback(av_log_default_callback);
     return result;

scripts/build-deps

@@ -69,7 +69,7 @@ echo ./configure
     --disable-bsfs \
     --enable-bsf=chomp,extract_extradata,h264_mp4toannexb,setts \
     --disable-filters \
-    --enable-filter=abuffer,abuffersink,aformat,aresample,atempo,buffer,buffersink,bwdif,color,lutrgb,palettegen,scale,testsrc,vflip,volume \
+    --enable-filter=abuffer,abuffersink,aformat,aresample,atempo,buffer,buffersink,bwdif,color,loudnorm,lutrgb,palettegen,scale,testsrc,vflip,volume \
     --enable-sse \
     --enable-avx \
     --enable-avx2 \