@@ -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
@@ -313,11 +314,16 @@ 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 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)
+ * - 0 for a more compact representation of a read only
+ * constant color frame
+ *
* For audio, size in bytes of each plane.
*
* For audio, only linesize[0] may be set. For planar audio, each channel
@@ -330,6 +336,9 @@ 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];
Signed-off-by: softworkz <softworkz@hotmail.com> --- libavutil/frame.h | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)