ffmpeg for DTS / DTS-HD to AC3 -> how much will quality suffer ?

[Darksoul71]

Hi all,

I am not shure wether this fits better here or over at the Linux forum.

@Mods: Feel free to move if my posting does not fit here !

Since two of my playback devices connected to my TV do not support DTS / DTS-HD audio (Raspberry Pi / Old WD TV Live), I decided to (down)convert the DTS audio streams inside my MKV files to multichannel AC3 and remux them. As I run Xubuntu 11.10 on my main box, I wanted to do the complete process under Linux.

I found this webpage providing details on how to convert DTS to AC3 with commandline tools under Linux:
http://juliensimon.blogspot.de/2009/01/howto-processing-multichannel-audio-dts.html

My small dirty python script works fine so far but one question remains for me:
Several of my BD backups are done with DTS-HD and unfortunately dcadec fails to decode them. At least my version of dcadec under Xubuntu. I found ffmpeg a well working solution for transcoding both DTS-HD and DTS streams to 5.1 AC3. On my TV and my PC with quite good headset the transcoded audio tracks sounded ok but one question remains though for me:
How much does audio quality suffer if one compares the original DTS / DTS-HD stream to the transcoded audio stream on 5.1 or 7.1 equipment ? Is the drop in quality noticable on consumer level hardware ?
Should I consider using different tools for audio transcoding ? May be eac3to inside Wine ?

TIA,
D$

[Asmodian]

I am not sure about the quality of ffmpeg (I believe eac3to uses Aften) and you never mentioned the bit-rate of the AC3 you were encoding to.

With that said, using eac3to, I cannot tell the difference after transcoding to a 640 kbps AC3 with headphones or a 5.1 system. I don't have 7.1 and none of my audio equipment, including my ears, is what I would call top of the line (it isn't terrible) but I understand this to be what most people have experienced.

I also understand AC3 to be better quality per size than DTS.

[tebasuna51]

- ffmpeg is now better encoder than Aften, but can't decode DTS-HD, only the standard DTS ('core') included in DTS-HD streams.

- In Windows, eac3to can use the ArcSoft decoder to decode DTS-HD and have a better quality source to encode. I don't now how can use ArcSoft decoder in Linux (DirectShow filters).

- To distinguish betwen lossles audio (DTS-HD Master Audio) and a AC3 640 Kb/s you need a good audio equipment (more than 1000€) and "golden ears"

[Darksoul71]

Asmodian, tebasuna51,

thanks for your replies. This gives me a better understanding.
Yes, sorry...I did not mention the bitrate I use for encoding. Usually my target bitrate is 448 kbBit/s. Since many if not most DVDs use this for their AC3 5.1 tracks I thought this might be sufficient. In the end I do not care too much about rasing this to 640 kBit if you mean this is important. Given the pure size of a standard BD rips in 1080p (mostly 7-12 GB with DTS streams) adding another 400 to 600 MB per AC3 track does not hurt me much :)

For the future I can hardly imagine more than using a cheap 5.1 system. I can only dream of a 1k€+ sound system and my ears are most definitely not "golden" anymore. As a result of this even completely throwing away DTS / DTS-HD inside the BD rip would not hurt much for my purposes.

Have a nice weekend,
D$