Thread worker: Error sending packet, when num_threads > 2

[AmphibianDev]

This is my test code

vr = decord.VideoReader('input\\videoS.webm', ctx=decord.cpu(0), num_threads=2)
for i in range(len(vr)):
    frame = vr[i]
    crop = frame.asnumpy()[500:550, 800:850]

When I put num_threads higher then 2 it throws a error, but only for some video files.

Traceback (most recent call last):
  File "c:\Users\GG\Desktop\LoL-OCR\test.py", line 12, in <module>
    frame = vr[i]
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\video_reader.py", line 105, in __getitem__
    return self.next()
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\video_reader.py", line 117, in next
    arr = _CAPI_VideoReaderNextFrame(self._handle)
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\_ffi\_ctypes\function.py", line 173, in __call__
    check_call(_LIB.DECORDFuncCall(
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\_ffi\base.py", line 78, in check_call
    raise DECORDError(err_str)
decord._ffi.base.DECORDError: [22:49:58] D:\a\decord\decord\src\video\ffmpeg\threaded_decoder.cc:292: [22:49:58] D:\a\decord\decord\src\video\ffmpeg\threaded_decoder.cc:218: Check failed: avcodec_send_packet(dec_ctx_.get(), pkt.get()) >= 0 (-11 vs. 0) Thread worker: Error sending packet.

And if I remove crop = frame.asnumpy()[500:550, 800:850] when num_threads is higher then 2 it throws this error and again only for some video files.

Traceback (most recent call last):
  File "c:\Users\GG\Desktop\LoL-OCR\test2.py", line 7, in <module>
    frame = vr[i]
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\video_reader.py", line 105, in __getitem__
    return self.next()
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\video_reader.py", line 117, in next
    arr = _CAPI_VideoReaderNextFrame(self._handle)
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\_ffi\_ctypes\function.py", line 173, in __call__
    check_call(_LIB.DECORDFuncCall(
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\_ffi\base.py", line 78, in check_call
    raise DECORDError(err_str)
decord._ffi.base.DECORDError: [22:57:11] D:\a\decord\decord\src\video\ffmpeg\threaded_decoder.cc:104: Check failed: run_.load()

• OS: Windows 10
• Conda: 22.9.0
• Python: 3.10.8
• Pip: 22.3.1
• Decord: 0.6.0
• Ffmpeg: 4.2.3

[chencuber]

This is my test code

vr = decord.VideoReader('input\\videoS.webm', ctx=decord.cpu(0), num_threads=2)
for i in range(len(vr)):
    frame = vr[i]
    crop = frame.asnumpy()[500:550, 800:850]

When I put num_threads higher then 2 it throws a error, but only for some video files.

Traceback (most recent call last):
  File "c:\Users\GG\Desktop\LoL-OCR\test.py", line 12, in <module>
    frame = vr[i]
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\video_reader.py", line 105, in __getitem__
    return self.next()
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\video_reader.py", line 117, in next
    arr = _CAPI_VideoReaderNextFrame(self._handle)
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\_ffi\_ctypes\function.py", line 173, in __call__
    check_call(_LIB.DECORDFuncCall(
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\_ffi\base.py", line 78, in check_call
    raise DECORDError(err_str)
decord._ffi.base.DECORDError: [22:49:58] D:\a\decord\decord\src\video\ffmpeg\threaded_decoder.cc:292: [22:49:58] D:\a\decord\decord\src\video\ffmpeg\threaded_decoder.cc:218: Check failed: avcodec_send_packet(dec_ctx_.get(), pkt.get()) >= 0 (-11 vs. 0) Thread worker: Error sending packet.

And if I remove crop = frame.asnumpy()[500:550, 800:850] when num_threads is higher then 2 it throws this error and again only for some video files.

Traceback (most recent call last):
  File "c:\Users\GG\Desktop\LoL-OCR\test2.py", line 7, in <module>
    frame = vr[i]
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\video_reader.py", line 105, in __getitem__
    return self.next()
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\video_reader.py", line 117, in next
    arr = _CAPI_VideoReaderNextFrame(self._handle)
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\_ffi\_ctypes\function.py", line 173, in __call__
    check_call(_LIB.DECORDFuncCall(
  File "C:\Users\GG\.conda\envs\LoL\lib\site-packages\decord\_ffi\base.py", line 78, in check_call
    raise DECORDError(err_str)
decord._ffi.base.DECORDError: [22:57:11] D:\a\decord\decord\src\video\ffmpeg\threaded_decoder.cc:104: Check failed: run_.load()

• OS: Windows 10
• Conda: 22.9.0
• Python: 3.10.8
• Pip: 22.3.1
• Decord: 0.6.0
• Ffmpeg: 4.2.3

Have you solve the problem？I encounter another issue（https://github.com/dmlc/decord/issues/262） which is similar with yours

[gtebbutt]

No closer to an overall fix, unfortunately, but in my testing this seems to occur consistently on VP9 encoded webm content, whereas mp4 and mkv containers are fine. Only workaround we've found so far is limiting to num_threads=2 on that input type.