Best practice for linear channel ingestion
After several years of working in the OTT business, we gathered plenty of experience regarding audio and video quality. When ingesting and transcoding a channel signal the following measurements have proven to guarantee a good outcome.
Although these guidelines were written primarily for working with the Magine in-house developed transcoder, they are for the most part universally applicable in the case of linear transcoding.
Bitrate
If the bitrate of the streams is low it causes compression artefacts. Usually, we receive HD channels at around 5-8 Mbit/s and convert them down to 3.6 Mbit/s. This reduces the streamed data size but maintains most of the picture quality. If your source material is not available at a higher quality we suggest setting the HD bitrate to at least 4 Mbit per channel. Keep in mind that higher resolutions require more bandwidth so if 4 Mbit/s would be the lower limit for 720p HD, around 2 Mbit/s should be OK for standard definition. If for some reason the bitrate cannot be increased the resolution needs to be decreased.
Resolution
Most important here is that each stream uses a fixed pixel resolution. This can never change unless you notify us in advance so we can agree on a specific time to make a change.
We also suggest using industry-standard resolutions such as 720x576 or 1280x720 etc. as we cannot guarantee that all possible resolutions will work on all devices. It is impossible to test all possible combinations, so please try to stick to industry standards. Please don't use resolutions lower than the normal standard definition as it will provide a poor viewing experience on screens larger than handheld.
It is also very important you don't upscale your source material when not necessary. If the program source material is SD the final broadcast stream should not be converted to HD. This practice will only decrease the perceived quality and artificially require a higher bitrate to maintain some of the quality. Unless a certain channel contains mostly HD content we suggest streaming it in SD resolution at a lower bitrate. As mentioned above, higher resolutions require a higher bitrate. But increasing the resolution will not necessarily increase perceived quality. A high bitrate but low-resolution stream will often look better than an overly compressed stream in higher resolution.
Aspect ratio
The aspect ratio of programs often differs on the same channel. Our system checks the aspect ratio per program in the source stream to make sure all programs are displayed accurately on different devices. If the aspect ratio metadata is wrong or missing it will affect the viewing experience for the end-user. This means all content will look distorted on all screens on all devices. The best solution is to pass the display aspect ratio through from the source material metadata and our clients will handle it correctly. If your metadata doesn't contain aspect ratio information you can set a static aspect ratio of 4:3 or 16:9. Choose the aspect ratio whichever is most suitable for the intended content on each channel.
Audio Video Timing and stuttering
For live streaming, it is important that audio and video can sync up when played back. It is equally important the audio and video data is sent at the same time. If audio and video are sent with a delay the playback device will play the content in sync. But it means that buffer space is used up by video content waiting for audio or vice versa. If the delay is longer than the buffer size the player will start dropping content and the stream will stutter or pause.
Broadcast schedules and stream status
Even if a channel is not broadcasting content at all times it would be helpful if the streams could be on air 24/7. We monitor all streams so we can act on errors. If the interruptions are not predictable we cannot monitor them and it will lead to unnecessary call-outs of our technicians which we will invoice you.