[FFmpeg-user] Impossible to convert between the formats supported by the filter 'Parsed_null_0' and the filter 'auto_scaler_0'

Garri Djavadyan garryd at comnet.uz
Wed Feb 14 23:58:48 EET 2018

On 2018-02-13 23:56, James Girotti wrote:
>> Recently, I faced transcoding issues with fully hardware nvdec/nvenc
>> scheme. Particularly, my FFmpeg feed fails with the following error 
>> after
>> 30-60 minutes of live transcoding:
> I have recently encountered this as well, but with DVD video material.
>> As I understand, some parameters change after 30-60 minutes in video
>> stream and FFmpeg tries to use software scaler in fully hardware 
>> scheme.
>> But I can't figure out exact reasons to act against the problem. I 
>> will be
>> very grateful if someone could direct me. I use following cmd line:
>> ---
>> /usr/local/ffmpeg/bin/ffmpeg -analyzeduration 100M -probesize 100M
>> -loglevel debug -hwaccel_device 1 -hwaccel cuvid -c:v h264_cuvid 
>> -deint 2
>> -drop_second_field 1 -i udp://
>> e=250000&overrun_nonfatal=1 -map p:1011:0 -map p:1011:1 -c:v 
>> h264_nvenc
>> -profile:v high -level 4.1 -b:v 2048k -c:a libfdk_aac -b:a 128k -af
>> aresample=async=1000 -f mpegts
> The solution I used was to drop the all the "hwaccel" parameters, still
> using hw-decoding and encoding. This does impact performance, but it
> ensures that if the stream contains material of a different pixel 
> format
> that the sws can correct it and transcoding will continue.

James, thank you very much for the advise. I've solved the issue using 
partially hardware transcoding (h264_cuvid -> system memory -> 
h264_nvenc), so the cmd line now is:

/usr/local/ffmpeg/bin/ffmpeg -analyzeduration 100M -probesize 100M 
-loglevel debug -c:v h264_cuvid -deint 2 -drop_second_field 1 -gpu 1 -i 
udp:// -map p:1011:0 
-map p:1011:1 -c:v h264_nvenc -gpu 1 -profile:v high -level 4.1 -b:v 
2048k -c:a libfdk_aac -b:a 128k -af aresample=async=1000 -f mpegts

> I'm not sure if this is a regression in ffmpeg/nvidia or just bad video
> material. I hadn't ever run into this until about a month ago. And it's
> happened on several videos from different DVD's. I didn't dig into it, 
> I
> just dropped the hwaccel parameters and moved on with my life. I wonder 
> if
> it's actually a problem in the hw-decoder, but I didn't see any error
> messages to prove that.

After migration to partially hardware transcoding, I don't see any calls 
for sws in debug log any more, but the following periodical messages 
from h264_cuvid:

[h264_cuvid @ 0x5616844a6c00] Format nv12 chosen by get_format().
[h264_cuvid @ 0x5616844a6c00] Formats: Original: nv12 | HW: nv12 | SW: 

I noticed that aspect ratio of TV programs changes over the time 
(visually) on the problem stream, but the actual SAR/DAR never changes 
(inspected by ffprobe periodically).


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