[FFmpeg-devel] [PATCH v2 2/2] avcodec/pngenc: write sBIT chunks

[Leo Izen <leo.izen@gmail.com>]

Add support for writing sBIT chunks, which mark the significant
bit depth of the PNG file. This obtains the metadata using the field
bits_per_raw_sample of AVCodecContext.

Signed-off-by: Leo Izen <leo.izen@gmail.com>
---
 libavcodec/pngenc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/libavcodec/pngenc.c b/libavcodec/pngenc.c
index 1489256d00..21b033ea16 100644
--- a/libavcodec/pngenc.c
+++ b/libavcodec/pngenc.c
@@ -442,6 +442,12 @@ static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
     if (png_get_gama(pict->color_trc, s->buf))
         png_write_chunk(&s->bytestream, MKTAG('g', 'A', 'M', 'A'), s->buf, 4);
 
+    if (avctx->bits_per_raw_sample > 0 && avctx->bits_per_raw_sample < s->bit_depth) {
+        int len = ff_png_get_nb_channels(s->color_type);
+        memset(s->buf, avctx->bits_per_raw_sample, len);
+        png_write_chunk(&s->bytestream, MKTAG('s', 'B', 'I', 'T'), s->buf, len);
+    }
+
     /* put the palette if needed, must be after colorspace information */
     if (s->color_type == PNG_COLOR_TYPE_PALETTE) {
         int has_alpha, alpha, i;
-- 
2.39.2

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