[FFmpeg-devel] [PATCH] avcodec/libjxlenc: support negative linesizes

[FFmpeg-devel] [PATCH] avcodec/libjxlenc: support negative linesizes

[Leo Izen]

libjxl doesn't support negative strides, but JPEG XL has an orientation
flag inside the codestream. We can use this to work around the library
limitation, by taking the absolute value of the negative row stride,
sending the image up-side-down, and telling the library that the image
has a vertical-flip orientation.

Signed-off-by: Leo Izen <leo.izen@gmail.com>
---
 libavcodec/libjxlenc.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/libavcodec/libjxlenc.c b/libavcodec/libjxlenc.c
index 67be8a01ca..49020b1036 100644
--- a/libavcodec/libjxlenc.c
+++ b/libavcodec/libjxlenc.c
@@ -259,6 +259,7 @@ static int libjxl_encode_frame(AVCodecContext *avctx, AVPacket *pkt, const AVFra
     size_t available = ctx->buffer_size;
     size_t bytes_written = 0;
     uint8_t *next_out = ctx->buffer;
+    uint8_t *data;
 
     ret = libjxl_init_jxl_encoder(avctx);
     if (ret) {
@@ -303,6 +304,7 @@ static int libjxl_encode_frame(AVCodecContext *avctx, AVPacket *pkt, const AVFra
 
     /* bitexact lossless requires there to be no XYB transform */
     info.uses_original_profile = ctx->distance == 0.0;
+    info.orientation = frame->linesize[0] >= 0 ? JXL_ORIENT_IDENTITY : JXL_ORIENT_FLIP_VERTICAL;
 
     if (JxlEncoderSetBasicInfo(ctx->encoder, &info) != JXL_ENC_SUCCESS) {
         av_log(avctx, AV_LOG_ERROR, "Failed to set JxlBasicInfo\n");
@@ -383,9 +385,15 @@ static int libjxl_encode_frame(AVCodecContext *avctx, AVPacket *pkt, const AVFra
     }
 
     jxl_fmt.endianness = JXL_NATIVE_ENDIAN;
-    jxl_fmt.align = frame->linesize[0];
+    if (frame->linesize[0] >= 0) {
+        jxl_fmt.align = frame->linesize[0];
+        data = frame->data[0];
+    } else {
+        jxl_fmt.align = -frame->linesize[0];
+        data = frame->data[0] - jxl_fmt.align * (info.ysize - 1);
+    }
 
-    if (JxlEncoderAddImageFrame(ctx->options, &jxl_fmt, frame->data[0], jxl_fmt.align * info.ysize) != JXL_ENC_SUCCESS) {
+    if (JxlEncoderAddImageFrame(ctx->options, &jxl_fmt, data, jxl_fmt.align * info.ysize) != JXL_ENC_SUCCESS) {
         av_log(avctx, AV_LOG_ERROR, "Failed to add Image Frame\n");
         return AVERROR_EXTERNAL;
     }
-- 
2.43.0

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Re: [FFmpeg-devel] [PATCH] avcodec/libjxlenc: support negative linesizes

[Tomas Härdin]

mån 2024-01-29 klockan 19:37 -0500 skrev Leo Izen:
> libjxl doesn't support negative strides, but JPEG XL has an
> orientation
> flag inside the codestream. We can use this to work around the
> library
> limitation, by taking the absolute value of the negative row stride,
> sending the image up-side-down, and telling the library that the
> image
> has a vertical-flip orientation.

Coincidentally we were just talking about negative stride on IRC
yesterday.

>      jxl_fmt.endianness = JXL_NATIVE_ENDIAN;
> -    jxl_fmt.align = frame->linesize[0];
> +    if (frame->linesize[0] >= 0) {
> +        jxl_fmt.align = frame->linesize[0];
> +        data = frame->data[0];
> +    } else {
> +        jxl_fmt.align = -frame->linesize[0];
> +        data = frame->data[0] - jxl_fmt.align * (info.ysize - 1);

Looks correct

/Tomas
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Re: [FFmpeg-devel] [PATCH] avcodec/libjxlenc: support negative linesizes

[Andreas Rheinhardt]

Leo Izen:
> libjxl doesn't support negative strides, but JPEG XL has an orientation
> flag inside the codestream. We can use this to work around the library
> limitation, by taking the absolute value of the negative row stride,
> sending the image up-side-down, and telling the library that the image
> has a vertical-flip orientation.
> 
> Signed-off-by: Leo Izen <leo.izen@gmail.com>
> ---
>  libavcodec/libjxlenc.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/libjxlenc.c b/libavcodec/libjxlenc.c
> index 67be8a01ca..49020b1036 100644
> --- a/libavcodec/libjxlenc.c
> +++ b/libavcodec/libjxlenc.c
> @@ -259,6 +259,7 @@ static int libjxl_encode_frame(AVCodecContext *avctx, AVPacket *pkt, const AVFra
>      size_t available = ctx->buffer_size;
>      size_t bytes_written = 0;
>      uint8_t *next_out = ctx->buffer;
> +    uint8_t *data;

Should be constified.

>  
>      ret = libjxl_init_jxl_encoder(avctx);
>      if (ret) {
> @@ -303,6 +304,7 @@ static int libjxl_encode_frame(AVCodecContext *avctx, AVPacket *pkt, const AVFra
>  
>      /* bitexact lossless requires there to be no XYB transform */
>      info.uses_original_profile = ctx->distance == 0.0;
> +    info.orientation = frame->linesize[0] >= 0 ? JXL_ORIENT_IDENTITY : JXL_ORIENT_FLIP_VERTICAL;
>  
>      if (JxlEncoderSetBasicInfo(ctx->encoder, &info) != JXL_ENC_SUCCESS) {
>          av_log(avctx, AV_LOG_ERROR, "Failed to set JxlBasicInfo\n");
> @@ -383,9 +385,15 @@ static int libjxl_encode_frame(AVCodecContext *avctx, AVPacket *pkt, const AVFra
>      }
>  
>      jxl_fmt.endianness = JXL_NATIVE_ENDIAN;
> -    jxl_fmt.align = frame->linesize[0];
> +    if (frame->linesize[0] >= 0) {
> +        jxl_fmt.align = frame->linesize[0];
> +        data = frame->data[0];
> +    } else {
> +        jxl_fmt.align = -frame->linesize[0];
> +        data = frame->data[0] - jxl_fmt.align * (info.ysize - 1);
> +    }
>  
> -    if (JxlEncoderAddImageFrame(ctx->options, &jxl_fmt, frame->data[0], jxl_fmt.align * info.ysize) != JXL_ENC_SUCCESS) {
> +    if (JxlEncoderAddImageFrame(ctx->options, &jxl_fmt, data, jxl_fmt.align * info.ysize) != JXL_ENC_SUCCESS) {
>          av_log(avctx, AV_LOG_ERROR, "Failed to add Image Frame\n");
>          return AVERROR_EXTERNAL;
>      }

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