Add a hack to FFmpegCapture for decoding Futatabi's Y'CbCr streams correctly.

[nageru] / futatabi / video_stream.cpp

diff --git a/futatabi/video_stream.cpp b/futatabi/video_stream.cpp
index 8f11714fb6d50bf863e37b9d5b531bbe0fbebe73..1957d8410d7a514618a9e51ad345ee933724d9ee 100644 (file)
--- a/futatabi/video_stream.cpp
+++ b/futatabi/video_stream.cpp
@@ -107,6 +107,10 @@ vector<uint8_t> encode_jpeg(const uint8_t *y_data, const uint8_t *cb_data, const
        cinfo.CCIR601_sampling = true;  // Seems to be mostly ignored by libjpeg, though.
        jpeg_start_compress(&cinfo, true);
 
+       // This comment marker is private to FFmpeg. It signals limited Y'CbCr range
+       // (and nothing else).
+       jpeg_write_marker(&cinfo, JPEG_COM, (const JOCTET *)"CS=ITU601", strlen("CS=ITU601"));
+
        JSAMPROW yptr[8], cbptr[8], crptr[8];
        JSAMPARRAY data[3] = { yptr, cbptr, crptr };
        for (unsigned y = 0; y < height; y += 8) {
@@ -234,7 +238,12 @@ VideoStream::~VideoStream() {}
 void VideoStream::start()
 {
        AVFormatContext *avctx = avformat_alloc_context();
-       avctx->oformat = av_guess_format("nut", nullptr, nullptr);
+
+       // We use Matroska, because it's pretty much the only mux where FFmpeg
+       // allows writing chroma location to override JFIF's default center placement.
+       // (Note that at the time of writing, however, FFmpeg does not correctly
+       // _read_ this information!)
+       avctx->oformat = av_guess_format("matroska", nullptr, nullptr);
 
        uint8_t *buf = (uint8_t *)av_malloc(MUX_BUFFER_SIZE);
        avctx->pb = avio_alloc_context(buf, MUX_BUFFER_SIZE, 1, this, nullptr, nullptr, nullptr);