[FFmpeg-devel] [PATCH v2] avcodec/libjxlenc: support negative linesizes

[FFmpeg-devel] [PATCH v2] 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..4ddd5f9f2c 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;
+    const 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 v2] avcodec/libjxlenc: support negative linesizes

[Leo Izen]

[-- Attachment #1.1.1: Type: text/plain, Size: 496 bytes --]

On 1/30/24 09:46, Leo Izen wrote:
> 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>
> ---

Changes from v1:

- constify uint8_t *data, per Andreas's request

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Re: [FFmpeg-devel] [PATCH v2] 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..4ddd5f9f2c 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;
> +    const 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);

Please don't rely on the type of jxl_fmt.align here (which is out of our
control). E.g. in the future it may be that libjxl supports only 32bit
align values (i.e. uses uint32_t or so for it), but that we support
64bit (ptrdiff_t) linesizes and allocations, so that jxl_fmt.align *
(info.ysize - 1) may overflow this even when -linesize fits into
jxl_fmt.align.
(Very unlikely given that align is size_t and they will likely not go
back from this, but it could happen.)

> +    }
>  
> -    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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Re: [FFmpeg-devel] [PATCH v2] avcodec/libjxlenc: support negative linesizes

[Leo Izen]

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On 1/30/24 09:57, Andreas Rheinhardt wrote:
> 
> Please don't rely on the type of jxl_fmt.align here (which is out of our
> control). E.g. in the future it may be that libjxl supports only 32bit
> align values (i.e. uses uint32_t or so for it), but that we support
> 64bit (ptrdiff_t) linesizes and allocations, so that jxl_fmt.align *
> (info.ysize - 1) may overflow this even when -linesize fits into
> jxl_fmt.align.
> (Very unlikely given that align is size_t and they will likely not go
> back from this, but it could happen.)
> 

This would be an ABI break though, wouldn't it? Why do we need to work 
around a potential future ABI break?

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Re: [FFmpeg-devel] [PATCH v2] avcodec/libjxlenc: support negative linesizes

[James Almer]

On 1/30/2024 12:06 PM, Leo Izen wrote:
> On 1/30/24 09:57, Andreas Rheinhardt wrote:
>>
>> Please don't rely on the type of jxl_fmt.align here (which is out of our
>> control). E.g. in the future it may be that libjxl supports only 32bit
>> align values (i.e. uses uint32_t or so for it), but that we support
>> 64bit (ptrdiff_t) linesizes and allocations, so that jxl_fmt.align *
>> (info.ysize - 1) may overflow this even when -linesize fits into
>> jxl_fmt.align.
>> (Very unlikely given that align is size_t and they will likely not go
>> back from this, but it could happen.)
>>
> 
> This would be an ABI break though, wouldn't it? Why do we need to work 
> around a potential future ABI break?

Point is, we have control over frame->linesize[0], but not over 
jxl_fmt.align, so the former is better to calculate offsets in our code.
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[FFmpeg-devel] [PATCH v3] 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..5f5f9751dc 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;
+    const 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] + frame->linesize[0] * (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 v3] avcodec/libjxlenc: support negative linesizes

[Leo Izen]

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On 1/30/24 10:24, Leo Izen wrote:
> +        jxl_fmt.align = -frame->linesize[0];
> +        data = frame->data[0] + frame->linesize[0] * (info.ysize - 1);
> +    }
>   

Something like this ^ is what you're requesting, right?

- Leo Izen (Traneptora)



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