BD Info is a quick and simplified way to view the overall encoding of a Blu-ray. This scan encompasses video, audio, and subtitle information, compiling it into one informational presentation. Video and audio have different ideal bitrate values, also depending on the type of disc that is being scanned. Blu-ray discs should have an ideal bitrate around 33000-40000 kbps; generally these bitrates tend to fluctuate throughout the film’s running time, which is why BD Info presents an average bitrate for the film’s codec.
Ideal audio Bitrates are variable depending on the type of codec; however, for lossless codecs like DTS-HD Master Audio or LPCM we would expect 1500-2450kbps. Lossy codecs have a much lower bitrate.
Subtitle bitrates are not relevant but the information does immediately present the various languages on the file.
Bitrate Viewer is a more precise view of the film’s video bitrate. The overall bitrate should match what is presented in BD Info (if we did everything correctly); however, instead of an average, Bitrate Viewer gives us a visual graph of the bitrate fluctuations throughout the duration of the movie. Ideally, we should see a fairly uniform bitrate spectrum throughout the course of the main feature, with lower values often occurring at the beginning and end of the film due to credit sequences.
We use BD Info and Bitrate Viewer in conjunction to get even more detail about the encoding. Bitrate Viewer is not able to capture codecs higher than H.264 (the usual Blu-ray codec), and so we are currently not able to scan UHDs with the software since that uses a H.265/HEVC codec. We are looking into possibilities for HEVC scanning in a similar method.
Note: as of 5/23/22 we have switched to exclusively using BD Info’s bitrate scan. This is so that we can see a comparison between 4K UHDs (which can only be scanned with BD Info) and Blu-rays.
Spek is a visual representation of the audio codec on the Blu-ray. Audio spectography is fairly complicated, but to simplify matters as much as possible, the graph possesses three different elements – kHz (frequency), which can be interpreted as the overall quality of the audio; dB (decibel) level, or the loudness of each audio wave; and the overall time of the film, represented in minutes. Each audio codec has a different maximum frequency that can be achieved; generally, lossless codecs will have a higher maximum frequency than lossy codecs, although it is possible to “fake” a lossless file, which is where Spek comes in to determine whether that has occurred.
For most, the frequency of the spectrogram will not be particularly compelling information unless you are a hardcore audiophile; however, the decibel levels can be a quick indication that there are volume issues with an audio file. Green and light blue colors are indicative of dialogue and audible music; the darker the color, the less audible, indicating more ambient textures.
While Spek can enlighten us to audio issues on discs, it is simply an indicator; the real test is to actually listen to the recording, especially since many minute audio changes are not noticeable to the average listener.
The color barcode is used to quickly assess variations in color grading between releases. It also looks cool as a unique visualization of the film’s color tone. Note: we do not apply color barcodes to 4K UHD releases because the HDR does not resample correctly, it takes a very long time to run the color sampling, and the comparisons between SDR Blu-ray and HDR UHD are not particularly relevant.
