H264 Testing Part 1
Here in New Zealand they have decided to use MPEG-4 (AVC/H264) for the broadcast of DTT (Digital Terrestrial Television). Selected broadcast tests have just started in Wellington and Christchurch, with occasional limited testing happening in other regions. At this stage the Auckland testing isn’t expected to start until January 2008, but luckily I’ve managed to source some test material from the Wellington tests.
For more details on the coverage and testing have a look at the following references -
Test Material
Many thanks to members of the NZ MythTV community for the test files. All screen shots were generated under Ubuntu Gutsy using MPlayer built off current SVN. The linked images are unscaled raw PNG images.
Clip 1 – SD 576i 16:9
Clip 2 – SD 576i 16:9
Clip 3 – HD 1080i
Clip 4 – HD 1080i
About the sample material
Based on the announcements from TVNZ that they would be standardising on 720p for TV One and TV 2 I was very surprised to see a bunch of 1080i samples. Perhaps TV3 are considering 1080i?
Another oddity is that the 1080i material is being transmitted at 1920x1080i with a 1:1 pixel mapping. Elsewhere in the world transmissions are usually 1440×1080 with the aspect ratio set to 16:9, making use of anamorphic scaling in the same was as DVD players.
The 576i material is being transmitted at 720x576i with 16:9 scaling to 1024x576i. This is similar to the existing SD MPEG2 broadcasts which transmit at 720x576i but use anamorphic scaling to show it in widescreen.
All of the tests are currently using standard MP2 audio streams between 192K and 256K. I’d like to see them will start using AC3 audio as part of the HD tests sometime soon.
I’ve heard that the existing test material was generated using standard PC based encoders. Hopefully someone can confirm this.
Lastly all of the material is making use of PAFF encoding, which is a more efficient way of delivering interlaced video. Sadly a lot of software decoders still don’t support PAFF, and it adds some additional overhead to the decoding PC.
Linux Playback Issues
Sadly there are currently lots of issues when attempting to play back this content under Linux.
- Standard distribution builds of MPlayer are based off RC1 or RC2, which don’t have support for PAFF.
- Current builds of MythTV don’t have a new enough build of ffmpeg for PAFF.
- VLC doesn’t currently support PAFF.
In the end I was able to get a build of MPlayer off SVN that could decode a couple of frames from the sample streams before it crashes.
I’ve also heard from Windows users who have similar issues with the sample streams. At present the only decoders reported as working are CoreAVC and PowerDVD.
Debugging MPlayer
Test OS is Ubuntu Gutsy with all current patches applied, running on an Athlon 64 X2 3600 with NVidia 6150 integrated graphics and the NVidia binary driver.
The build of MPlayer came off SVN and is tagged as
MPlayer dev-SVN-r25017-4.1.3
You can find sample debug output of MPlayer trying to play the first clip here.
The error we see thrown around the crash is as follows
[h264 @ 0x88bcaf0]warning: first frame is no keyframe
[h264 @ 0x88bcaf0]warning: first frame is no keyframe
[h264 @ 0x88bcaf0]Internal error, picture buffer overflow
At this stage I think we need to supply some of the sample material onto the MPlayer and ffmpeg team for further analysis as the other test files crash in exactly the same fashion.
If you have any additional info about the tests please get in touch via my OpenMedia contact address, or catch me on the MythTV NZ mailing list or the GeekZone Home Theater Forum.