Re: [FFmpeg-devel] [PATCH v4 2/4] avcodec/jpegxl_parser: add JPEG XL parser

[Leo Izen <leo.izen@gmail.com>]

On 6/27/23 18:58, James Almer wrote:
> On 6/26/2023 12:49 PM, Leo Izen wrote:
>> +/*
>> + * copies as much of the codestream into the buffer as possible
>> + * pass a shorter buflen to request less
>> + * returns the number of bytes consumed from input, may be greater 
>> than input_len
>> + * if the input doesn't end on an ISOBMFF-box boundary
>> + */
>> +int ff_jpegxl_collect_codestream_header(const uint8_t *input_buffer, 
>> int input_len,
>> +                                        uint8_t *buffer, int buflen, 
>> int *copied)
>> +{
>> +    GetByteContext gb;
>> +    int pos = 0;
>> +    bytestream2_init(&gb, input_buffer, input_len);
>> +
>> +    while (1) {
>> +        uint64_t size;
>> +        uint32_t tag;
>> +        int head_size = 8;
>> +
>> +        if (bytestream2_get_bytes_left(&gb) < 16)
>> +            break;
>> +
>> +        size = bytestream2_get_be32(&gb);
>> +        if (size == 1) {
>> +            size = bytestream2_get_be64(&gb);
>> +            head_size = 16;
>> +        }
>> +        /* invalid ISOBMFF size */
>> +        if (size && size <= head_size)
>> +            return AVERROR_INVALIDDATA;
> 
> ISOBMFF? Are you propagating container bytes as if they were part of the 
> bitstream from image2? Why is it not being handled by the mov/mp4 
> demuxer instead?

It's not actually ISOBMFF, it just uses the same style of box layout. 
This is also how j2k works.

> 
>> +    if (ctx->meta.csp == JPEGXL_CS_GRAY) {
>> +        if (ctx->meta.bit_depth <= 8)
>> +            avctx->pix_fmt = s->format = ctx->meta.have_alpha ? 
>> AV_PIX_FMT_YA8 : AV_PIX_FMT_GRAY8;
>> +        else if (ctx->meta.bit_depth <= 16)
>> +            avctx->pix_fmt = s->format = ctx->meta.have_alpha ? 
>> AV_PIX_FMT_YA16 : AV_PIX_FMT_GRAY16;
>> +        else
>> +            avctx->pix_fmt = s->format = ctx->meta.have_alpha ? 
>> AV_PIX_FMT_NONE : AV_PIX_FMT_GRAYF32;
>> +    } else {
>> +        if (ctx->meta.bit_depth <= 8)
>> +            avctx->pix_fmt = s->format = ctx->meta.have_alpha ? 
>> AV_PIX_FMT_RGBA : AV_PIX_FMT_RGB24;
>> +        else if (ctx->meta.bit_depth <= 16)
>> +            avctx->pix_fmt = s->format = ctx->meta.have_alpha ? 
>> AV_PIX_FMT_RGBA64 : AV_PIX_FMT_RGB48;
>> +        else
>> +            avctx->pix_fmt = s->format = ctx->meta.have_alpha ? 
>> AV_PIX_FMT_RGBAF32 : AV_PIX_FMT_RGBF32;
> 
> Again, don't fill avctx->pix_fmt, fill s->format.
> _______________________________________________

If I don't fill this, the CLI will not show the pixel format without the 
external decoder library enabled. Should I consider this an ffmpeg.c bug?

- Leo Izen

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