Bad interleave causes stuttering playback due to gap events

[kdwk]

Successor to #82

After reporting the issue to GStreamer, it is discovered that "[the transcoded] file is quite badly muxed" and "this bad interleave causes us to send gap events that already advance the playback time, so the actual video frames then arrive almost 5s late".

Upstream issue in GStreamer is https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/4264#note_2805727

[sdroege]

You can see that with mkvinfo -a FWIW:

|+ Cluster
| + Cluster timestamp: 00:00:00.000000000
| + Simple block: key, track number 2, 1 frame(s), timestamp 00:00:00.000000000
|  + Frame with size 3
| + Simple block: key, track number 2, 1 frame(s), timestamp 00:00:00.021000000
|  + Frame with size 3
| + Simple block: key, track number 2, 1 frame(s), timestamp 00:00:00.041000000
[...]
| + Simple block: key, track number 2, 1 frame(s), timestamp 00:00:04.861000000
|  + Frame with size 288
|+ Cluster
| + Cluster timestamp: 00:00:04.881000000
| + Simple block: key, track number 2, 1 frame(s), timestamp 00:00:04.881000000
|  + Frame with size 490
| + Simple block: key, track number 1, 1 frame(s), timestamp 00:00:00.000000000           <---------- first video frame
|  + Frame with size 14089
| + Simple block: key, track number 2, 1 frame(s), timestamp 00:00:04.901000000

[gianni-rosato]

Thanks for the detailed issue report.

How should I go about fixing this? I'm still not convinced that this is an Aviator issue, as all that Aviator does is generate an FFmpeg command and run it based on a couple of specific parameters:

            cmd = [
                "ffmpeg",
                "-nostdin",
                "-hide_banner",
                "-loglevel", "info",
                "-y",
                "-i", self.source_file_absolute,
                vfilters_prefix,
                vfilters,
                "-map", "0:v",
                "-c:v", "libsvtav1",
                "-crf", str(int(self.crf_scale.get_value())),
                "-preset", str(int(self.speed_scale.get_value())),
                "-pix_fmt", "yuv420p10le",
                "-svtav1-params", f"film-grain={int(self.grain_scale.get_value())}:" + f"tune={tune}:" + f"psy-rd={psyrd}:" + "input-depth=10:enable-qm=1:qm-min=0:keyint=300:aq-mode=2:" + f"irefresh-type={gop_val}:" + f"film-grain-denoise={denoise_val}",
                "-map", "0:a?",
                "-c:a", "copy" if self.audio_copy_switch.get_state() else "libopus",
                "-mapping_family", "1",
                "-b:a", self.bitrate_entry.get_text() + "K",
                afilters_prefix,
                afilters,
                "-ac", "2" if self.downmix_switch.get_state() else "0",
                "-map", "0:s?" if self.container == "mkv" else "-0:s",
                "-c:s", "copy",
                "-metadata", "comment=\"Encoded with Aviator\"",
                output,
            ]

If there's anything in here that could be problematic, let me know.

[sdroege]

You'd have to debug your usage of ffmpeg then and/or report this to ffmpeg. For example, does this also happen if you run ffmpeg like this manually? Does it happen if you omit the video filters and/or audio filters? Does it happen with a different encoder (rav1e, x264)?

[gianni-rosato]

OK, good to know – thanks for the help