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

[Lynne via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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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.

> 
> 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.

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