On Sun, 14 Nov 2021, Soft Works wrote:
Signed-off-by: softworkz <softwo...@hotmail.com>
---
v3: fixed patch, removed comment about 0 line size
libavutil/frame.h | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/libavutil/frame.h b/libavutil/frame.h
index ff2540a20f..31def23d8b 100644
--- a/libavutil/frame.h
+++ b/libavutil/frame.h
@@ -304,7 +304,8 @@ typedef struct AVFrame {
#define AV_NUM_DATA_POINTERS 8
/**
* pointer to the picture/channel planes.
- * This might be different from the first allocated byte
+ * This might be different from the first allocated byte. For video,
+ * it could even point to the end of the image data.
*
* Some decoders access areas outside 0,0 - width,height, please
* see avcodec_align_dimensions2(). Some filters and swscale can read
@@ -313,12 +314,20 @@ typedef struct AVFrame {
*
* NOTE: Except for hwaccel formats, pointers not needed by the format
* MUST be set to NULL.
+ *
+ * @attention In case of video, the data[] pointers can point to the
+ * end of image data in order to reverse line order, when used in
+ * combination with negative values in the linesize[] array.
*/
uint8_t *data[AV_NUM_DATA_POINTERS];
/**
- * For video, size in bytes of each picture line.
- * For audio, size in bytes of each plane.
+ * For video, a positive or negative value, which is typically indicating
+ * the size in bytes of each picture line, but it can also be:
+ * - the negative byte size of lines for vertical flipping
+ * (with data[n] pointing to the end of the data
+ * - a positive or negative multiple of the byte size as for accessing
+ * even and odd fields of a frame (possibly flipped)
*
* For audio, only linesize[0] may be set. For planar audio, each channel
* plane must be the same size.
@@ -330,6 +339,9 @@ typedef struct AVFrame {
*
* @note The linesize may be larger than the size of usable data -- there
* may be extra padding present for performance reasons.
+ *
+ * @attention In case of video, line size values can be negative to achieve
+ * a vertically inverted iteration over image lines.
*/
int linesize[AV_NUM_DATA_POINTERS];
Thanks, will apply.
Regards,
Marton
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