v10 no longer writes "rotate" metadata flag

[FirefoxMetzger]

Overview

As of v10.0.0 the stream metadata flag rotate is no longer written to file. This may affect other metadata fields; however, for this one specifically, we have a unit-test downstream so I know for sure that it is affected.

Expected behavior

Setting a field in a video stream's metadata dict causes it to be written to the file.

Actual behavior

Stream-level metadata (at least the rotation flag) is no longer written.

Reproduction

import av
import numpy as np

print(f"PyAV version: {av.__version__}")

with av.open("test.mp4", "w") as container:
    container.metadata["comment"] = "This video has a rotation flag."

    stream = container.add_stream("libx264", 24)
    stream.metadata["rotate"] = "90"

    for _ in range(24):
        frame = av.VideoFrame.from_ndarray(np.ones((128, 128, 3), dtype=np.uint8))
        for packet in stream.encode(frame):
            container.mux(packet)

    for packet in stream.encode():
        container.mux(packet)

with av.open("test.mp4") as container:
    print(container.metadata)
    video_stream = container.streams.video[0]
    print(video_stream.metadata)

Using av v9.2 the above snippet produces:

PyAV version: 9.2.0
{'major_brand': 'isom', 'minor_version': '512', 'compatible_brands': 'isomiso2avc1mp41', 'encoder': 'Lavf58.76.100', 'comment': 'This video has a rotation flag.'}
{'rotate': '90', 'language': 'und', 'handler_name': 'VideoHandler', 'vendor_id': '[0][0][0][0]'}

However, when switching to v10 it produces:

PyAV version: 10.0.0
{'major_brand': 'isom', 'minor_version': '512', 'compatible_brands': 'isomiso2avc1mp41', 'encoder': 'Lavf59.27.100', 'comment': 'This video has a rotation flag.'}
{'language': 'und', 'handler_name': 'VideoHandler', 'vendor_id': '[0][0][0][0]'}

Versions

• OS: Windows 11 and Ubuntu 20.04
• PyAV runtime:

PyAV v10.0.0
library configuration: --disable-static --enable-shared --libdir=/c/cibw/vendor/lib --prefix=/c/cibw/vendor --disable-alsa --disable-doc --disable-mediafoundation --enable-fontconfig --enable-gmp --disable-gnutls --enable-gpl --enable-libaom --enable-libass --enable-libbluray --enable-libdav1d --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --disable-libxcb --enable-libxml2 --enable-libxvid --enable-lzma --enable-version3 --enable-zlib
library license: GPL version 3 or later
libavcodec     59. 37.100
libavdevice    59.  7.100
libavfilter     8. 44.100
libavformat    59. 27.100
libavutil      57. 28.100
libswresample   4.  7.100
libswscale      6.  7.100

• FFmpeg: (pypi shipped binary)

Research

I have done the following:

• Checked the PyAV documentation
• Searched on Google
• Searched on Stack Overflow
• Looked through old GitHub issues
• Asked on PyAV Gitter
• ... and waited 72 hours for a response.

[hmaarrfk]

Does this also affect conda-forge? it may be that something is wrong with the bundled ffmpeg. conda-forge I believe has allowed ffmpeg 5 with pyav 9.2

[hmaarrfk]

I tried it with conda-forge builds. i can indeed recreate.

• av 10.0.0 + conda-forge. No rotation flag.
• av 9.2.0 + conda-forge. rotation flag.
• av 10.0.0 + [streams] populate added stream with codec param (fixes #1044) #1062. No rotation flag

It seems to be a bug in the pyav implementation, not the bundled ffmpeg libraries.

[hmaarrfk]

It may be that ffmpeg 5 deprecated these options:
https://ffmpeg.org/pipermail/ffmpeg-devel/2022-May/296553.html

[hmaarrfk]

Ok digging around in this, I think that the ffmpeg command, uses:

    if (ost->rotate_overridden) {
        uint8_t *sd = av_stream_new_side_data(ost->st, AV_PKT_DATA_DISPLAYMATRIX,
                                              sizeof(int32_t) * 9);
        if (sd)
            av_display_rotation_set((int32_t *)sd, -ost->rotate_override_value);
    }

but i'm not too sure...

[hmaarrfk]

This isn't a bug so much as it is a "PyAV/we" need to update to the new API.

The old "rotate" flag (that they consider hack) needs to be updated.

FFmpeg/FFmpeg@ddef3d9

FFmpeg/FFmpeg@7b6012e

[HanzCEO]

rotate metadata are indeed deprecated.

diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
index 0d1c84d6df..5a00886e05 100644
--- a/fftools/ffmpeg_opt.c
+++ b/fftools/ffmpeg_opt.c
@@ -2916,6 +2916,7 @@ loop_end:
             for (j = 0; j < oc->nb_streams; j++) {
                 ost = output_streams[nb_output_streams - oc->nb_streams + j];
                 if ((ret = check_stream_specifier(oc, oc->streams[j], stream_spec)) > 0) {
+#if FFMPEG_ROTATION_METADATA
                     if (!strcmp(o->metadata[i].u.str, "rotate")) {
                         char *tail;
                         double theta = av_strtod(val, &tail);
@@ -2923,9 +2924,18 @@ loop_end:
                             ost->rotate_overridden = 1;
                             ost->rotate_override_value = theta;
                         }
+
+                        av_log(NULL, AV_LOG_WARNING,
+                               "Conversion of a 'rotate' metadata key to a "
+                               "proper display matrix rotation is deprecated. "
+                               "See -display_rotation for setting rotation "
+                               "instead.");
                     } else {
+#endif
                         av_dict_set(&oc->streams[j]->metadata, o->metadata[i].u.str, *val ? val : NULL, 0);
+#if FFMPEG_ROTATION_METADATA
                     }
+#endif
                 } else if (ret < 0)
                     exit_program(1);
             }
--

It won't be set by av_dict_set() but instead get converted into display matrix rotation.

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[WyattBlue]

Although the api is different now, #1249 should address this. All major ffmpeg point releases I expect would have these breaking changes, including the upcoming ffmpeg 7.0.