Normalize unspecified PCM channel layouts before AAC setup

src/video/video.c

@@ -526,6 +526,11 @@ static int vc_open_audio(struct vc_ctx* ctx) {
     struct vc_stream* stream = &ctx->audio;
     AVCodecContext* decoder = stream->decoder;
     if (decoder->sample_rate <= 0 || decoder->ch_layout.nb_channels <= 0) return AVERROR_INVALIDDATA;
+    if (decoder->ch_layout.order == AV_CHANNEL_ORDER_UNSPEC) {
+        int channels = decoder->ch_layout.nb_channels;
+        av_channel_layout_default(&decoder->ch_layout, channels);
+        DEBUG_INFO(DEBUG_CATEGORY_VIDEO, "video audio uses default layout for %d unspecified channels", channels);
+    }
     const AVCodec* codec = avcodec_find_encoder(AV_CODEC_ID_AAC);
     if (!codec) return AVERROR_ENCODER_NOT_FOUND;
     stream->encoder = avcodec_alloc_context3(codec);