SAR is ignored on AV1 anamorphic video

[lilole]

• Platform: Linux 6.16.7-arch1-1 SMP PREEMPT_DYNAMIC Thu, 11 Sep 2025 17:42:36 +0000 x86_64 GNU/Linux

• MythTV version: v35.0-33-g931474b3a0
  Also see mythtv_version.txt

• Package version: 35.0.r33.g931474b3a0-1, Arch Linux AUR https://aur.archlinux.org/packages/mythtv-git

• Component: Frontend

What steps will reproduce the bug?

1. Create or find a Matroska file with an AV1 video stream, at 720x480, SAR 32:27, DAR 16:9.
   I created a sample that shows this issue: https://drive.google.com/file/d/1QdWG3aIlNyqrrpom9-IsSceQWuwfIpOV/view?usp=sharing
2. Add this file to a dir configured in MythTV Backend for video file storage.
3. Navigate to Watch Videos in the Frontend, and select this file.
4. Play the file. The width is not stretched by the proper 32:27 (1.185x) amount.

How often does it reproduce? Is there a required condition?

This has happened on all the AV1 videos I have processed so far with these dimensions and SAR in a MKV container.

I notice on my frontend system, the playback is using Ffmpeg, not VAAPI.

What is the expected behaviour?

The video should be automatically stretched horizontally by 1.185x, by the player honoring the 32:27 SAR property. On many other videos I own, processed to H.264 video streams, this was never an issue, and the SAR was always honored. But I have switched to using AV1 encoding now, to backup my remaining content which I own.

What do you see instead?

The video plays fine, and audio is fine, but the video is horizontally "squished", leaving black bars on each side of the screen. I can manually force "16:9" aspect ratio in the Playback context menu, and then the video is stretched, so it seems the Ffmpeg player is capable of doing the right thing.

Additional information

I also saw this issue on the previous version of MythTV I had. But I upgraded to the latest stable to be sure (in fact I reinstalled my whole MythTV server with a new drive).

If there is any workaround anyone can provide, like some hidden config setting for the Ffmpeg player, that would be great. For now the only workaround I can think of to "fix" this automatically is to stretch the video as I process it, forcing the SAR to 1:1, but this wastes extra storage on the enlarged frames without increasing quality.

[lilole]

Under the What steps will reproduce... section, I forgot to add "Scan for changes" in Step 3, before you can watch the file.

[lilole]

By the way, MythTV is pretty awesome.

[bennettpeter]

Your sample video does not play at all. I tried vlc and mythfrontend. No video, only audio.

[lilole]

Your sample video does not play at all. I tried vlc and mythfrontend. No video, only audio. Mediainfo shows it is AVC not AV1.

I wonder if goog somehow changed it. Just making sure, were you able to click the download button from the goog drive page? In my case it does seem to be able to download intact.

[bennettpeter]

Actually, I can play it with VLC if I force FFmpeg decoding. It was trying to use VDPAU

[lilole]

The MKV file size should be 82,338,070, and its sha256 should be:
baf9f0459c62f47474d132fc13c24412b066cbc132a2d91a241ba4fe59d2d8f7

[bennettpeter]

sha256sum '/home/storage/Video/mythtv-local/videos/Samples/av1_sar_issue_test.mkv'
009867363331f69bbc2880881f6cee4a09d1f45b5a25fb402ac588398fc940d4 /home/storage/Video/mythtv-local/videos/Samples/av1_sar_issue_test.mkv

Plays with vlc if I force FFmpeg but not with mythfrontend

[lilole]

Ah sorry you're right, I had the wrong sum. Your sum is what I have.

[lilole]

...
Plays with vlc if I force FFmpeg but not with mythfrontend

Hmm I did notice that my frontend says "ffmpeg" in the video info as it plays, where it usually says "vaapi". Sorry I don't know how my frontend is special somehow.

I notice that ffmpeg is built as part of my MythTV package, AND I have ffmpeg version n7.1.1 installed system wide.

[lilole]

$ ls -l /usr/bin/mythff*
-rwxr-xr-x 1 root root 338096 Sep 14 14:47 /usr/bin/mythffmpeg
-rwxr-xr-x 1 root root 189904 Sep 14 14:47 /usr/bin/mythffprobe

I was assuming this was the ffmpeg that my frontend uses. But I don't really know.

[lilole]

More details:

$ mythffmpeg -version
ffmpeg version v35.0-33-g931474b3a0 Copyright (c) 2000-2024 the FFmpeg developers
built with gcc 15.2.1 (GCC) 20250813
configuration: --arch=x86 --sysinclude=/usr/include --cc=gcc --cxx=g++ --ld=gcc --cpu=x86-64 --target_os=linux --pkg_config=pkg-config --prefix=/usr --libdir=/usr/lib --as=gcc --objcc=gcc --dep_cc=gcc --host_cc=gcc --host_ld=gcc --ar=ar --nm='nm -g' --ranlib='ranlib -D' --disable-cross-compile --enable-libmp3lame --enable-libx264 --enable-libx265 --enable-libvpx --disable-libxvid --enable-vdpau --enable-libxml2 --enable-libass --disable-dxva2 --enable-libbluray --disable-libfontconfig --disable-libfreetype --disable-libiec61883 --disable-sdl2 --disable-ffplay --enable-vaapi --enable-libaom --enable-libdav1d --enable-gnutls --enable-libdrm --extra-cflags= --extra-ldflags= --extra-libs= --disable-stripping --disable-manpages --disable-podpages --disable-doc --disable-nvenc --enable-shared --disable-static --enable-gpl --enable-pic --disable-demuxer=mpegtsraw --disable-indev=dshow
libavutil      59. 39.100 / 59. 39.100
libavcodec     61. 19.100 / 61. 19.100
libavformat    61.  7.100 / 61.  7.100
libavdevice    61.  3.100 / 61.  3.100
libavfilter    10.  4.100 / 10.  4.100
libswscale      8.  3.100 /  8.  3.100
libswresample   5.  3.100 /  5.  3.100
libpostproc    58.  3.100 / 58.  3.100

[bennettpeter]

Latest master of mythfrontend will not play the clip
MythTV Version : v36-Pre-518-gab57738caf
I get this error repeated maany times:
E [90575/91674] Decoder avformatdecoder.cpp:3300:ProcessVideoPacket AFD: video avcodec_send_packet error: Function not implemented (-38) gotpicture:0

[bennettpeter]

I cannot play it with mythfrontend v35 either
MythTV Version : v35.0-20-g9e66243fbd
I gett the same error
AFD: video avcodec_send_packet error: Function not implemented (-38) gotpicture:0

[paul-h]

I'm a bit out of touch with current MythTV but in order to get AV1 support to be included you had to add --enable-libdav1d to the compile flags and install the relevant dependencies so our ffmpeg will include support for it. Don't know if that is still required or not. Also not sure if we ever updated the Ubuntu PPA builder to include it or if any other packagers add that compile flag I know it was discussed at some point?

For reference here is an old forum post about it
https://forum.mythtv.org/viewtopic.php?p=25664#p25664

[lilole]

All the build options that were used can be found in the PKGBUILD file under https://aur.archlinux.org/packages/mythtv-git.

On my system, in the cached copy of PKGBUILD, I see this, along with A LOT of other stuff:

   ./configure --prefix=/usr \
               --cpu="$ARCH" \
               --disable-altivec \
               --enable-audio-jack \
               --disable-distcc \
               --enable-libmp3lame \
               --enable-libvpx \
               --enable-libx264 \
               --enable-libx265 \
               --enable-vaapi \
               --with-bindings=python \
               --with-bindings=perl \
               --perl-config-opts=INSTALLDIRS=vendor