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avutil/frame: Document the possibility of negative line sizes

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Signed-off-by: softworkz <softworkz@hotmail.com>
Signed-off-by: Marton Balint <cus@passwd.hu>
This commit is contained in:
Soft Works 2021-11-14 20:15:56 +00:00 committed by Marton Balint
parent 9181b9ec7c
commit daef8cbff7
1 changed files with 15 additions and 3 deletions
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18
libavutil/frame.h
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@ -311,7 +311,8 @@ typedef struct AVFrame {
#define AV_NUM_DATA_POINTERS 8 #define AV_NUM_DATA_POINTERS 8
/** /**
* pointer to the picture/channel planes. * 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 * Some decoders access areas outside 0,0 - width,height, please
* see avcodec_align_dimensions2(). Some filters and swscale can read * see avcodec_align_dimensions2(). Some filters and swscale can read
@ -320,12 +321,20 @@ typedef struct AVFrame {
* *
* NOTE: Except for hwaccel formats, pointers not needed by the format * NOTE: Except for hwaccel formats, pointers not needed by the format
* MUST be set to NULL. * 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]; 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
* For audio, size in bytes of each plane. * 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 * For audio, only linesize[0] may be set. For planar audio, each channel
* plane must be the same size. * plane must be the same size.
@ -337,6 +346,9 @@ typedef struct AVFrame {
* *
* @note The linesize may be larger than the size of usable data -- there * @note The linesize may be larger than the size of usable data -- there
* may be extra padding present for performance reasons. * 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]; int linesize[AV_NUM_DATA_POINTERS];