Problems with reencoding HEVC videos on 14.0.0 and 14.0.1

[dumbledore]

I am observing two problems when reencoding HEVC videos on 14.0.0 and 14.0.1 on Windows 11 (haven't tried on Ubuntu or MacOS so far):

1. Reencoding HEVC videos produces videos with artefacts: They start OK for a second and then they look quite broken and don't recover. I haven't verified if this is actually a decoding issue, but I don't think so.
2. Using the default SLICED threading model very often (but not always) blocks indefinitely on Packet.decode() for HEVC. CTRL+C is ignored. I haven't been able to reproduce the freeze-up with FRAME threading.

Neither issue is observed with H264.

Here is how to reproduce it:

import av
import av.datasets
import os

# I need this on windows as by default it goes to a system folder which needs admin permissions
os.environ["PYAV_TESTDATA_DIR"] = os.getcwd()

av.logging.set_level(av.logging.VERBOSE)


def test(input_filename, output_filename, thread_type=None):
    print(f"{os.path.basename(input_filename)} -> {os.path.basename(output_filename)} thread_type={thread_type}")
    with av.open(input_filename) as in_container:
        with av.open(output_filename, "w") as output_container:
            in_stream = in_container.streams.video[0]

            if thread_type:
                in_stream.thread_type = thread_type

            out_stream = output_container.add_stream_from_template(in_stream)

            print(in_stream)
            print(out_stream)

            for packet in in_container.demux(in_stream):
                print(f"Demuxed {packet}")

                if packet.dts is None:
                    continue

                for frame in packet.decode():
                    print(f"Decoded {frame}")

                    frame = out_stream.encode(frame)
                    if (frame):
                        print(f"Encoded {frame}")
                        output_container.mux(frame)

    print("Done")

h264_filename = av.datasets.curated("pexels/time-lapse-video-of-night-sky-857195.mp4")
hevc_filename = av.datasets.cached_download("http://fate-suite.ffmpeg.org/hevc/dv84.mov", "dv84.mov")

# Re-encoding H264 for the curated video works fine both with sliced and frame threading
test(h264_filename, "h264-sliced.mp4")
test(h264_filename, "h264-frame.mp4", "FRAME")

# Re-encoding HEVC/X265 produces shorter video with artefacts. It is OK only for a second.
test(hevc_filename, "hevc-frame.mov", "FRAME")

# Re-encoding HEVC/X265 using SLICE often blocks at packet.decode() and CTRL+C does not work
test(hevc_filename, "hevc-sliced.mov")

See log.txt for the output.

Actually, to reproduce the blocking issue, it is enough to call Packet.decode() enough times:

import av
import av.datasets
import os

# I need this on windows as by default it goes to a system folder which needs admin permissions
os.environ["PYAV_TESTDATA_DIR"] = os.getcwd()

av.logging.set_level(av.logging.VERBOSE)


def test(input_filename, it):
    with av.open(input_filename) as in_container:
        in_stream = in_container.streams.video[0]

        idx = 1
        for packet in in_container.demux(in_stream):
            print(f"#{it} Demuxed #{idx} {packet}")

            if packet.dts is None:
                continue

            print(f"#{it} Decoding...")
            packet.decode()
            idx += 1


hevc_filename = av.datasets.cached_download("http://fate-suite.ffmpeg.org/hevc/dv84.mov", "dv84.mov")

it = 1
while True:
    print(f"Try {it}...")
    test(hevc_filename, it)
    it += 1

[JoeSchiff]

Similar issues on Linux

I did some testing on Ubuntu 24.04. Both problems occur as you described, but with some differences.

Using the first script: the code will hang when using either FRAME or SLICE threading.

Using the second script: calling Packet.decode() is not enough to reproduce the blocking issue. I ran hundreds of iterations without hanging.

Misc notes

When I use the ffmpeg installed through apt (not bundled with pyav), the code does not hang, but the artifacts still occur.

I noticed the video will always hang at the same spot for a given thread type.
For example, SLICE always hangs here:
Demuxed <av.Packet of #0, dts=59, pts=160; 62043 bytes at 0x7f48eda41170>

FRAME hangs here:
Demuxed <av.Packet of #0, dts=1340, pts=1441; 63442 bytes at 0x77e03110d990>

[nagadomi]

On my Ubuntu, I get the same deadlock problem with the second script (no modification).
It does not occur with av==13.1.0.
I suspect this is a ffmpeg side issue( ? ), but I wonder what the developer's opinion is.

[johan-sightic]

I did not have this problem yesterday but today .decode() hangs all the time. I have not updated ffmpeg or PyAV manually but i did install nvidia-cuda-toolkit and the latest Ubuntu updates.
Setting stream.thread_type = "FRAME" makes the hanging go away

[WyattBlue]

hangs all the time
Ubuntu

many such cases

[nagadomi]

On my Ubuntu, I get the same deadlock problem with the second script (no modification).

I have confirmed that this problem has been fixed in 14.1.0.