Re: [FFmpeg-devel] [PATCH] lavu/stereo3d: change baseline and horizontal FOV to rationals

[James Almer <jamrial@gmail.com>]

On 6/22/2024 6:26 PM, Lynne via ffmpeg-devel wrote:
> On 22/06/2024 22:19, James Almer wrote:
>> On 6/22/2024 5:11 PM, Lynne via ffmpeg-devel wrote:
>>> This avoids hardcoding any implementation-specific limitiations as
>>> part of the API, and allows for future expandability.
>>>
>>> This also allows API users to more conveniently convert the
>>> values into floats without hardcoding specific conversion constants.
>>>
>>> The draft implementation of this mechanism for the draft of
>>> AVTransport uses rationals for these particular fields.
>>>
>>> The API was committed 2 days ago, so changing these fields now
>>> is within the realms of acceptable.
>>> ---
>>>   fftools/ffprobe.c                            |  4 ++--
>>>   libavformat/dump.c                           |  9 +++++----
>>>   libavformat/mov.c                            |  9 ++++++---
>>>   libavutil/stereo3d.h                         |  8 ++++----
>>>   tests/ref/fate/matroska-spherical-mono       |  4 ++--
>>>   tests/ref/fate/matroska-spherical-mono-remux |  8 ++++----
>>>   tests/ref/fate/matroska-stereo_mode          | 16 ++++++++--------
>>>   tests/ref/fate/matroska-vp8-alpha-remux      |  4 ++--
>>>   tests/ref/fate/mov-spherical-mono            |  4 ++--
>>>   9 files changed, 35 insertions(+), 31 deletions(-)
>>>
>>> diff --git a/fftools/ffprobe.c b/fftools/ffprobe.c
>>> index d7ba980ff9..2da928b7c3 100644
>>> --- a/fftools/ffprobe.c
>>> +++ b/fftools/ffprobe.c
>>> @@ -2546,9 +2546,9 @@ static void print_pkt_side_data(WriterContext *w,
>>>               print_int("inverted", !!(stereo->flags & 
>>> AV_STEREO3D_FLAG_INVERT));
>>>               print_str("view", av_stereo3d_view_name(stereo->view));
>>>               print_str("primary_eye", 
>>> av_stereo3d_primary_eye_name(stereo->primary_eye));
>>> -            print_int("baseline", stereo->baseline);
>>> +            print_q("baseline", stereo->baseline, '/');
>>>               print_q("horizontal_disparity_adjustment", stereo- 
>>> >horizontal_disparity_adjustment, '/');
>>> -            print_int("horizontal_field_of_view", stereo- 
>>> >horizontal_field_of_view);
>>> +            print_q("horizontal_field_of_view", stereo- 
>>> >horizontal_field_of_view, '/');
>>>           } else if (sd->type == AV_PKT_DATA_SPHERICAL) {
>>>               const AVSphericalMapping *spherical = 
>>> (AVSphericalMapping *)sd->data;
>>>               print_str("projection", 
>>> av_spherical_projection_name(spherical->projection));
>>> diff --git a/libavformat/dump.c b/libavformat/dump.c
>>> index 61a2c6a29f..ac7d3038ab 100644
>>> --- a/libavformat/dump.c
>>> +++ b/libavformat/dump.c
>>> @@ -262,13 +262,14 @@ static void dump_stereo3d(void *ctx, const 
>>> AVPacketSideData *sd, int log_level)
>>>       av_log(ctx, log_level, "%s, view: %s, primary eye: %s",
>>>              av_stereo3d_type_name(stereo->type), 
>>> av_stereo3d_view_name(stereo->view),
>>>              av_stereo3d_primary_eye_name(stereo->primary_eye));
>>> -    if (stereo->baseline)
>>> -        av_log(ctx, log_level, ", baseline: %"PRIu32"", stereo- 
>>> >baseline);
>>> +    if (stereo->baseline.num && stereo->baseline.den)
>>> +        av_log(ctx, log_level, ", baseline: %d/%d", stereo- 
>>> >baseline.num, stereo->baseline.den);
>>>       if (stereo->horizontal_disparity_adjustment.num && stereo- 
>>> >horizontal_disparity_adjustment.den)
>>>           av_log(ctx, log_level, ", horizontal_disparity_adjustment: 
>>> %d/%d",
>>>                  stereo->horizontal_disparity_adjustment.num, stereo- 
>>> >horizontal_disparity_adjustment.den);
>>> -    if (stereo->horizontal_field_of_view)
>>> -        av_log(ctx, log_level, ", horizontal_field_of_view: 
>>> %"PRIu32"", stereo->horizontal_field_of_view);
>>> +    if (stereo->horizontal_field_of_view.num && stereo- 
>>> >horizontal_field_of_view.den)
>>> +        av_log(ctx, log_level, ", horizontal_field_of_view: %d/%d", 
>>> stereo->horizontal_field_of_view.num,
>>> +               stereo->horizontal_field_of_view.den);
>>>       if (stereo->flags & AV_STEREO3D_FLAG_INVERT)
>>>           av_log(ctx, log_level, " (inverted)");
>>> diff --git a/libavformat/mov.c b/libavformat/mov.c
>>> index f08fec3fb6..64cd17e770 100644
>>> --- a/libavformat/mov.c
>>> +++ b/libavformat/mov.c
>>> @@ -6545,7 +6545,8 @@ static int mov_read_eyes(MOVContext *c, 
>>> AVIOContext *pb, MOVAtom atom)
>>>       MOVStreamContext *sc;
>>>       int size, flags = 0;
>>>       int64_t remaining;
>>> -    uint32_t tag, baseline = 0;
>>> +    uint32_t tag;
>>> +    AVRational baseline = av_make_q(0, 0);
>>>       enum AVStereo3DView view = AV_STEREO3D_VIEW_PACKED;
>>>       enum AVStereo3DPrimaryEye primary_eye = AV_PRIMARY_EYE_NONE;
>>>       AVRational horizontal_disparity_adjustment = { 0, 1 };
>>> @@ -6642,7 +6643,8 @@ static int mov_read_eyes(MOVContext *c, 
>>> AVIOContext *pb, MOVAtom atom)
>>>               avio_skip(pb, 1); // version
>>>               avio_skip(pb, 3); // flags
>>> -            baseline = avio_rb32(pb);
>>> +            baseline.num = avio_rb32(pb);
>>> +            baseline.den = 1000000; // micrometers
>>>               break;
>>>           }
>>> @@ -6782,7 +6784,8 @@ static int mov_read_hfov(MOVContext *c, 
>>> AVIOContext *pb, MOVAtom atom)
>>>               return AVERROR(ENOMEM);
>>>       }
>>> -    sc->stereo3d->horizontal_field_of_view = avio_rb32(pb);
>>> +    sc->stereo3d->horizontal_field_of_view.num = avio_rb32(pb);
>>> +    sc->stereo3d->horizontal_field_of_view.den = 1000; // thousands 
>>> of a degree
>>>       return 0;
>>>   }
>>> diff --git a/libavutil/stereo3d.h b/libavutil/stereo3d.h
>>> index 00a5c3900e..097f6c9455 100644
>>> --- a/libavutil/stereo3d.h
>>> +++ b/libavutil/stereo3d.h
>>> @@ -213,9 +213,9 @@ typedef struct AVStereo3D {
>>>       /**
>>>        * The distance between the centres of the lenses of the camera 
>>> system,
>>> -     * in micrometers. Zero if unset.
>>> +     * in meters. Zero if unset.
>>>        */
>>> -    uint32_t baseline;
>>> +    AVRational baseline;
>>
>> This is not ok. No reason for distance be a soft float, or allow 
>> negative values. In the case of the blin box, it's a 32bit unsigned 
>> value, which will not fit in AVRational.
> 
> Added an (int32_t) cast locally. This is also how 
> horizontal_disparity_adjustment is handled, with a uint32_t converted 
> into a rational.

No, that one is an int32_t as it can be negative (Ranges -1.0 to 1.0), 
thus it works fine as AVRational. baseline does not, so it should stay 
an uint32_t.

> 
>>
>> You can easily convert this in your code by using a 1000000 
>> denominator if you wish.
>>
>>>       /**
>>>        * Relative shift of the left and right images, which changes 
>>> the zero parallax plane.
>>> @@ -224,9 +224,9 @@ typedef struct AVStereo3D {
>>>       AVRational horizontal_disparity_adjustment;
>>>       /**
>>> -     * Horizontal field of view in thousanths of a degree. Zero if 
>>> unset.
>>> +     * Horizontal field of view, in degrees. Zero if unset.
>>>        */
>>> -    uint32_t horizontal_field_of_view;
>>> +    AVRational horizontal_field_of_view;
>>
>> This one i can't say. Would for example Matroska implement degrees as 
>> a float, or uint?
> 
> Likely a float (EBML_FLOAT). This is how mastering metadata and video 
> projection are handled.

But Mastering metadata is not in degrees.

Wait for Derek to comment. He knows this field better than me.

> 
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