Why do stream downloaders have different results?

[DWreck1995]

For example, lets say I download a stream with VLC, then with JDownloader, and they complete with different file sizes. How can the files be different sizes if they're not set to convert anything?

This happens with other downloaders to, such as, youtube-dl, IDM, etc...

I'm trying to understand if it's me missing a setting, or if there's a logical reason why a supposedly untouched video could be a different size depending on the program.

[jagabo]

Multiplexing the audio and video streams often involves padding to better align data for quicker access. Different programs may pad differently. And they may include different metadata. And of course, different containers have different overhead.

[DWreck1995]

Multiplexing the audio and video streams often involves padding to better align data for quicker access. Different programs may pad differently. And they may include different metadata. And of course, different containers have different overhead.

I see. Thanks for mentioning that. So could the padding process affect the video stream bitrate as well? I've also noticed a larger discrepancy between two downloaders results when an HLS stream is comprised of a lot of parts. I'm not sure if that's correlated or not either.

[blud7]

Some downloaders re-encode the audio or video streams on the fly based on your output preference. Check to see that you are not re-encoding.

[DWreck1995]

Some downloaders re-encode the audio or video streams on the fly based on your output preference. Check to see that you are not re-encoding.

I tried to make sure as best I could that no re-encoding was occurring throughout my testing.

With VLC, I can check a box that allows it to "keep original" for the video and audio streams. With youtube-dl I can add strings to the commands to ensure it doesn't re-encode. But nonetheless, they both produce different sized files of the same stream. Doesn't make sense...

[jagabo]

You can always verify if the actual video and audio streams are identical with various tools. MSU VQMT, ffmpeg, AviSynth, etc.

[DWreck1995]

You can always verify if the actual video and audio streams are identical with various tools. MSU VQMT, ffmpeg, AviSynth, etc.

I'm not familiar with any of those, besides ffmpeg. Would you mind elaborating on which tool would be easiest to work with and how I could use it for verifying video/audio streams?

[jagabo]

Here's a batch file that uses ffmpeg to calculate a psnr value:

"g:\program files\ffmpeg64\bin\ffmpeg" -i %1 -i %2 -lavfi "[0:v][1:v]psnr" -f null -
Pause

Put that text in batch file. Change the path to wherever ffmpeg is on your computer. Then drag/drop a pair of videos onto the batch file. The higher the PSNR value the more similar they are. A perfect match is "inf".

[DWreck1995]

Here's a batch file that uses ffmpeg to calculate a psnr value:

"g:\program files\ffmpeg64\bin\ffmpeg" -i %1 -i %2 -lavfi "[0:v][1:v]psnr" -f null -
Pause

Put that text in batch file. Change the path to wherever ffmpeg is on your computer. Then drag/drop a pair of videos onto the batch file. The higher the PSNR value the more similar they are. A perfect match is "inf".

Thanks for the batch file. I'm not sure if I did something incorrectly or if my ffmpeg build is missing something, but I get the following output when I run the batch file:

C:\Windows\system32>"c:\program files\ffmpeg64\bin\ffmpeg" -i -i -lavfi "[0:v][1:v]psnr" -f null -
ffmpeg version 2022-06-22-git-fed07efcde-full_build-www.gyan.dev Copyright (c) 2000-2022 the FFmpeg developers
built with gcc 11.3.0 (Rev1, Built by MSYS2 project)
configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libdav1d --enable-libdavs2 --enable-libuavs3d --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxvid --enable-libaom --enable-libjxl --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-libshaderc --enable-vulkan --enable-libplacebo --enable-opencl --enable-libcdio --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora --enable-libtwolame --enable-libvo-amrwbenc --enable-libilbc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint
libavutil 57. 27.100 / 57. 27.100
libavcodec 59. 33.100 / 59. 33.100
libavformat 59. 25.100 / 59. 25.100
libavdevice 59. 6.100 / 59. 6.100
libavfilter 8. 41.100 / 8. 41.100
libswscale 6. 6.100 / 6. 6.100
libswresample 4. 6.100 / 4. 6.100
libpostproc 56. 5.100 / 56. 5.100
-i: No such file or directory

C:\Windows\system32>Pause
Press any key to continue . . .

[jagabo]

C:\Windows\system32>"c:\program files\ffmpeg64\bin\ffmpeg" -i -i -lavfi "[0:v][1:v]psnr" -f null -

That indicates you ran the batch file with no inputs. You have to drag and drop a pair of videos onto the batch file -- so it knows which two files to compare.

[DWreck1995]

C:\Windows\system32>"c:\program files\ffmpeg64\bin\ffmpeg" -i -i -lavfi "[0:v][1:v]psnr" -f null -

That indicates you ran the batch file with no inputs. You have to drag and drop a pair of videos onto the batch file -- so it knows which two files to compare.

Thanks for clarifying. I was dragging them into the open window of the batch file instead of dragging them on to the batch file icon.

I ran a file that was 2897 MB when downloaded though VLC and 2857 MB when downloaded though youtube-dl. The PSNR value was indeed "inf". This would indicate that even though there's a 40 MB difference between the two files, with different audio and video bitrates, they're still exactly the same quality?

[jagabo]

I ran a file that was 2897 MB when downloaded though VLC and 2857 MB when downloaded though youtube-dl. The PSNR value was indeed "inf". This would indicate that even though there's a 40 MB difference between the two files, with different audio and video bitrates, they're still exactly the same quality?

Yes. A PSNR around 50 is a pretty good (re)encoding. Around 40 is youtube quality. Lower than that is getting pretty bad. Also, the videos must have the same properties: the same frame size, same number of frames, etc.

The bitrate reported by different programs can vary depending on many factors. Don't count on it being accurate.

[DWreck1995]

I ran a file that was 2897 MB when downloaded though VLC and 2857 MB when downloaded though youtube-dl. The PSNR value was indeed "inf". This would indicate that even though there's a 40 MB difference between the two files, with different audio and video bitrates, they're still exactly the same quality?

Yes. A PSNR around 50 is a pretty good (re)encoding. Around 40 is youtube quality. Lower than that is getting pretty bad. Also, the videos must have the same properties: the same frame size, same number of frames, etc.

The bitrate reported by different programs can vary depending on many factors. Don't count on it being accurate.

So if there was any differences than the higher the number the more alike they are? Does it also specify which of the two would be the higher quality one as well?

That's interesting. I've been using MediaInfo to compare them to see what differences they may have. I didn't know that the bitrate could be so unreliable.

[jagabo]

So if there was any differences than the higher the number the more alike they are?

Yes.

Does it also specify which of the two would be the higher quality one as well?

No. Though, in the way it's usually used (comparing an encoded video to the original) you already know which is of higher quality.