[mythtv] FFmpeg 4.4.1 problems

Mon Nov 22 18:07:09 UTC 2021

tl;dr Also blocking artifacts when skipping with mpv when VDPAU is used.
Blocking artifacts with vlc when using VDPAU but also when NOT using VDPAU.
Blocking artifacts with mplayer.
Failed to create a MythTV with an unmodified FFmpeg tree.

And this is the long version....

I have been doing some more tests with mpv and this time with various
options.
The file used for testing, tweevoortwaalf-ffmpeg.ts, has been shared in
this thread.
Note that this file is the first 100Mbyte of a mythtv recording and it is
representative of what is here on the local cable network, it is not a
sequence specially crafted to test decoders.

This plays OK:
$ mpv tweevoortwaalf-ffmpeg.ts
$ mpv -vo vdpau tweevoortwaalf-ffmpeg.ts
$ mpv -vo=gpu tweevoortwaalf_ffmpeg.ts
$ mpv --hwdec=vdpau tweevoortwaalf_ffmpeg.ts
$ mpv -vo=gpu --hwdec=vdpau tweevoortwaalf_ffmpeg.ts

This gives blocking artifacts with skipping:
$ mpv -vo=vdpau --hwdec=vdpau tweevoortwaalf_ffmpeg.ts
$ mpv --vo=gpu --hwdec=vdpau-copy tweevoortwaalf_ffmpeg.ts

This is the mpv version used, as present in Fedora 35.
[klaas at modu videos]$ mpv -version
mpv 0.34.0 Copyright © 2000-2021 mpv/MPlayer/mplayer2 projects
 built on UNKNOWN
FFmpeg library versions:
   libavutil       56.70.100
   libavcodec      58.134.100
   libavformat     58.76.100
   libswscale      5.9.100
   libavfilter     7.110.100
   libswresample   3.9.100
FFmpeg version: 4.4.1

This plays correct but while it uses Nvidia hardware it does NOT use VDPAU
as pointed out by Peter:
$ ffplay -sst 0 -vcodec h264_cuvid tweevoortwaalf_ffmpeg.ts

But interesting: playback with VLC also gives blocking artifacts!
VLC uses VDPAU by default as shown here:
[klaas at modu videos]$ vlc tweevoortwaalf_ffmpeg.ts
VLC media player 3.0.16 Vetinari (revision 3.0.13-8-g41878ff4f2)
[0000560ed8f70b70] main libvlc: Running vlc with the default interface. Use
'cvlc' to use vlc without interface.
[00007fd348005720] gl gl: Initialized libplacebo v4.157.0 (API v157)
libva info: VA-API version 1.13.0
libva info: Trying to open /usr/lib64/dri/nvidia_drv_video.so
libva info: Found init function __vaDriverInit_1_12
libva info: va_openDriver() returns 0
[00007fd348005720] glconv_vaapi_x11 gl error: vaCreateSurfaces: attribute
not supported
[00007fd344077100] main video output error: video output creation failed
[00007fd354c10f90] main decoder error: failed to create video output
[00007fd3484ada50] gl gl: Initialized libplacebo v4.157.0 (API v157)
[00007fd354c10f90] avcodec decoder: Using NVIDIA VDPAU Driver Shared
Library  495.44  Fri Oct 22 06:03:50 UTC 2021 for hardware decoding

Further complicating the issue is that when playing the same clip on
another system with Intel built-in graphics, VLC also gives the blocking
artifacts.

Next test with the mplayer: also blocking artifacts when skipping for all
tested video output options (vdpau, xv, x11, gl).
[klaas at modu videos]$ mplayer tweevoortwaalf_ffmpeg.ts
MPlayer SVN-r38302-11 (C) 2000-2021 MPlayer Team
do_connect: could not connect to socket
connect: No such file or directory
Failed to open LIRC support. You will not be able to use your remote
control.

Playing tweevoortwaalf_ffmpeg.ts.
libavformat version 58.76.100 (external)
TS file format detected.
VIDEO H264(pid=2301) AUDIO MPA(pid=2311) SUB Teletext(pid=2401)  PROGRAM N.
1
FPS seems to be: 25.000000
==========================================================================
Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
libavcodec version 58.134.100 (external)
Selected video codec: [ffh264] vfm: ffmpeg (FFmpeg H.264)
==========================================================================
Load subtitles in ./
==========================================================================
Requested audio codec family [mpg123] (afm=mpg123) not available.
Enable it at compilation.
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 48000 Hz, 2 ch, floatle, 256.0 kbit/8.33% (ratio: 32000->384000)
Selected audio codec: [ffmp2float] afm: ffmpeg (FFmpeg MPEG layer-1 and
layer-2 audio)
==========================================================================
AO: [pulse] 48000Hz 2ch floatle (4 bytes per sample)
Starting playback...
Bad stream state, please report as bug!
Bad stream state, please report as bug!
Movie-Aspect is 1.78:1 - prescaling to correct movie aspect.
VO: [vdpau] 1920x1080 => 1920x1080 Planar YV12
A:71555.4 V:71556.4 A-V: -0.948 ct:  0.000   2/  2 ??% ??% ??,?% 0 0
Bad stream state, please report as bug!
Bad stream state, please report as bug!
Bad stream state, please report as bug!
Bad stream state, please report as bug!

It looks like skipping correctly in these transport streams with H264 1080
interlaced is not trivial.
However, mythfrontend has been skipping correctly for the last 15 years up
to and including the current master.
So it should be feasible to get this working also with the latest FFmpeg.

In order to start somewhere I have replaced, in a copy of the current
master, the FFmpeg tree with the latest FFmpeg master and then hacked away
in the MythTV code so that it could work with an (almost) unmodified ffmpeg
tree.
The great plan behind this is:
- If it shows blocking behaviour then bisect the ffmpeg from the latest
version to something that is close to what is now in master. This is why I
want ffmpeg master because there is then a linear sequence of commits
instead of a tree.
- If it does NOT show blocking behaviour then add the MythTV changes one by
one and check for blocking behaviour.

However, while compilation is now OK, linking fails with unresolved symbols.
These are symbols that do show up as global in the object file but then are
local when included in the .so file.
Example, for a file that I did add to libavcodec (that is the "almost"
unmodified):

[klaas at modu libavcodec]$ nm libmythavcodec.so | grep ff_codec_type
00000000006b4200 t ff_codec_type_string
[klaas at modu libavcodec]$ nm utils-mythtv.o | grep ff_codec_type
0000000000000940 T ff_codec_type_string
[klaas at modu libavcodec]$ readelf -s utils-mythtv.o | grep ff_codec_type
   181: 0000000000000940   128 FUNC    GLOBAL DEFAULT    1
ff_codec_type_string
[klaas at modu libavcodec]$ readelf -s libmythavcodec.so | grep ff_codec_type
 20731: 00000000006b4200   128 FUNC    LOCAL  DEFAULT   12
ff_codec_type_string

Note that there are more unresolved who are not from a file that I added.
This is the complete list from linking programs/mythavtest:
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ffurl_close'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ffurl_seek'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ffurl_open'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ff_ue_golomb_vlc_code'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ffurl_write'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ffurl_read'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ff_se_golomb_vlc_code'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ff_read_frame_flush'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ff_codec_type_string'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ffurl_size'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ff_golomb_vlc_len'
/usr/bin/ld: ../../libs/libmythtv/libmythtv-32.so: undefined reference to
`ff_codec_id_string'
The two ff_codec_.. functions are in file avcodec/utils-mythtv.c and they
can be moved to outside FFmpeg.
I would have done that if it were the only unresolved symbols.

This is basically where the project is currently halted....

Klaas.
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