Fix writing of planar audio to export buffers in some cases (#2223).

Previously we did not take into account alignment padding that can
exist with FLTP samples; each channel's block of samples can have
a gap between.  This doesn't happen with the normal 1024 sample blocks;
only when flushing at the end, when we write shorter blocks.

Not doing this right meant that we were passing uninitialised memory
to aacenc which sometimes responded by returning an EINVAL due to one
of its internal calculations returning a NaN.

diff --git a/src/lib/ffmpeg_file_encoder.cc b/src/lib/ffmpeg_file_encoder.cc
index 705557f799b3b76f434eb182fe116b4a32b03e85..6f13f5dd606eff5375c8b2338e8ade11a6e47353 100644 (file)
--- a/src/lib/ffmpeg_file_encoder.cc
+++ b/src/lib/ffmpeg_file_encoder.cc
@@ -134,7 +134,8 @@ public:
                auto frame = av_frame_alloc ();
                DCPOMATIC_ASSERT (frame);
 
-               int const buffer_size = av_samples_get_buffer_size (0, channels, size, _codec_context->sample_fmt, 0);
+               int line_size;
+               int const buffer_size = av_samples_get_buffer_size (&line_size, channels, size, _codec_context->sample_fmt, 0);
                DCPOMATIC_ASSERT (buffer_size >= 0);
 
                auto samples = av_malloc (buffer_size);
@@ -169,10 +170,8 @@ public:
                }
                case AV_SAMPLE_FMT_FLTP:
                {
-                       float* q = reinterpret_cast<float*> (samples);
                        for (int i = 0; i < channels; ++i) {
-                               memcpy (q, data[i + channel_offset], sizeof(float) * size);
-                               q += size;
+                               memcpy (reinterpret_cast<float*>(static_cast<uint8_t*>(samples) + i * line_size), data[i + channel_offset], sizeof(float) * size);
                        }
                        break;
                }