Hi Phil,
Unfortunately I cannot share the sample we use internally, but it should be
reproducible with any h.263/mpeg-4 encoded file & hw accelerated decoding.
Thanks
Stefan
-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of Philip
Langdale
Sent: Saturday, August 3, 2019 08:57
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH] Fixing HW accelerated decoders hanging or
throwing error in h263dec
On 2019-08-03 00:09, Timo Rothenpieler wrote:
> On 02.08.2019 11:18, Stefan Schoenefeld wrote:
>> Hi all,
>>
>> Recently we encountered an issue when decoding a h.263 file:
>>
>> FFmpeg will freeze when decoding h.263 video with NVDEC. Turns out
>> this is not directly related to NVDEC but is a problem that shows
>> with several other HW decoders like VDPAU, though the exact kind of
>> error is different (either error messages or freezing[1]). The root
>> cause is that ff_thread_finish_setup() is called twice per frame from
>> ff_h263_decode_frame(). This is not supported by
>> ff_thread_finish_setup() and specifically checked for and warned
>> against in the functions code. The issue is also specific to hw
>> accelerated decoding only as the second call to
>> ff_thread_finish_setup() is only issued when hw acceleration is on.
>> The fix is simple: add a check that the first call is only send when
>> hw acceleration is off, and the second call only when hw acceleration
>> is on (see attached patch). This works fine as far as I was able to
>> test with vdpau and nvdec/nvcuvid hw decoding. The patch also adds
>> NVDEC to the hw config list if available.
>>
>> I also noticed a secondary issue when browsing through the code which
>> is that, according to documentation, ff_thread_finish_setup() should
>> only be called if the codec implements update_thread_context(), which
>> h263dec does not. The patch does not address this and I'm not sure
>> any action needs to be taken here at all.
>>
>> Thanks,
>> Stefan
>>
>> [1] This is depending on whether or not the hw decoder sets the
>> HWACCEL_CAPS_ASYNC_SAFE flag
>>
>> From 0620ee777a8ba98145bb4781e30a77687c97dbf8 Mon Sep 17 00:00:00
>> 2001
>> From: Stefan Schoenefeld <sschoenef...@nvidia.com>
>> Date: Fri, 2 Aug 2019 10:52:22 +0200
>> Subject: [PATCH] Fixing HW accelerated decoders hanging or throwing
>> error messages in h263dec
>>
>> ---
>> libavcodec/h263dec.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavcodec/h263dec.c b/libavcodec/h263dec.c index
>> 6f001f6..8ee844e 100644
>> --- a/libavcodec/h263dec.c
>> +++ b/libavcodec/h263dec.c
>> @@ -614,7 +614,7 @@ retry:
>> if ((ret = ff_mpv_frame_start(s, avctx)) < 0)
>> return ret;
>> - if (!s->divx_packed)
>> + if (!s->divx_packed && !avctx->hwaccel)
>> ff_thread_finish_setup(avctx);
>
> This seems correct to me, but I'd like another pair of eyes to look
> over it.
Seems fine to me as well.
>
>> if (avctx->hwaccel) {
>> @@ -747,6 +747,9 @@ const AVCodecHWConfigInternal
>> *ff_h263_hw_config_list[] = { #if CONFIG_H263_VAAPI_HWACCEL
>> HWACCEL_VAAPI(h263),
>> #endif
>> +#if CONFIG_MPEG4_NVDEC_HWACCEL
>> + HWACCEL_NVDEC(mpeg4),
>> +#endif
>
> Probably cleaner to split this into its own patch, but otherwise OK.
>
>> #if CONFIG_MPEG4_VDPAU_HWACCEL
>> HWACCEL_VDPAU(mpeg4),
>> #endif
Thanks for fixing this. I was always confused about whether h.263 was really
supported by the hardware or not. Can you provide a link to a reference sample
that fails without this change and succeeds with it?
--phil
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