Ffmpeg Live Transcoding From TS To MXF Loose Audio/video Sync

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Introduction

In this article, we will discuss the process of live transcoding from TS (Transport Stream) to MXF (Material eXchange Format) using ffmpeg, while addressing the issue of loose audio/video sync. This solution is designed to run on Amazon Linux 2 in the AWS eu-west-3 region, utilizing two ffmpeg-based systemd services on a c5.2xlarge EC2 instance.

Background

Our video recording system has been experiencing audio/video drift, which can be caused by various factors such as differences in clock rates between the audio and video streams, or issues with the synchronization process. To resolve this issue, we have implemented a live transcoding solution using ffmpeg, which will convert the TS stream to MXF format in real-time.

System Configuration

The system is running on Amazon Linux 2, which provides a stable and secure environment for our ffmpeg-based services. The EC2 instance is a c5.2xlarge, which offers a high-performance computing environment with 8 vCPUs and 16 GB of RAM. This configuration ensures that our live transcoding process can handle high-bandwidth streams without any performance issues.

ffmpeg-based Systemd Services

We have created two systemd services, one for each stream (audio and video), to handle the live transcoding process. Each service is responsible for reading the TS stream, transcoding it to MXF format, and writing the output to a file. The services are designed to run in parallel, ensuring that the audio and video streams are synchronized correctly.

Service 1: Audio Transcoding

The first service, audio-transcode.service, is responsible for transcoding the audio stream from TS to MXF format. The service uses the following ffmpeg command:

ffmpeg -i input.ts -c:a aac -b:a 128k -ar 48000 -ac 2 -f mxf output.mxf

This command reads the input TS stream, extracts the audio stream, and transcodes it to AAC format with a bitrate of 128 kbps. The output is written to an MXF file with a sample rate of 48 kHz and 2 channels.

Service 2: Video Transcoding

The second service, video-transcode.service, is responsible for transcoding the video stream from TS to MXF format. The service uses the following ffmpeg command:

ffmpeg -i input.ts -c:v h264 -b:v 10M -f mxf output.mxf

This command reads the input TS stream, extracts the video stream, and transcodes it to H.264 format with a bitrate of 10 Mbps. The output is written to an MXF file.

Synchronization

To ensure that the audio and video streams are synchronized correctly, we use a synchronization mechanism based on the timestamp of the TS stream. The timestamp is extracted from the TS stream and used to synchronize the audio and video streams during the transcoding process.

Implementation

The implementation of the live transcoding solution involves the following steps:

  1. TS Stream Input: The TS stream is read from a file or a network source.
  2. Audio and Video Extraction: audio and video streams are extracted from the TS stream using ffmpeg.
  3. Transcoding: The audio and video streams are transcoded to MXF format using ffmpeg.
  4. Synchronization: The audio and video streams are synchronized based on the timestamp of the TS stream.
  5. Output: The synchronized audio and video streams are written to an MXF file.

Conclusion

In this article, we have discussed the process of live transcoding from TS to MXF format using ffmpeg, while addressing the issue of loose audio/video sync. The solution is designed to run on Amazon Linux 2 in the AWS eu-west-3 region, utilizing two ffmpeg-based systemd services on a c5.2xlarge EC2 instance. The implementation involves the extraction of audio and video streams from the TS stream, transcoding to MXF format, and synchronization based on the timestamp of the TS stream. The solution provides a high-quality live transcoding process with synchronized audio and video streams.

Troubleshooting

In case of any issues with the live transcoding process, the following troubleshooting steps can be taken:

  • Check TS Stream Input: Verify that the TS stream is being read correctly from the file or network source.
  • Check Audio and Video Extraction: Verify that the audio and video streams are being extracted correctly from the TS stream.
  • Check Transcoding: Verify that the audio and video streams are being transcoded correctly to MXF format.
  • Check Synchronization: Verify that the audio and video streams are being synchronized correctly based on the timestamp of the TS stream.

Future Work

In the future, we plan to improve the live transcoding solution by:

  • Optimizing Transcoding Performance: Optimizing the transcoding process to improve performance and reduce latency.
  • Implementing Error Handling: Implementing error handling mechanisms to handle any issues that may arise during the transcoding process.
  • Supporting Multiple Input Formats: Supporting multiple input formats, such as MP4 and AVI, in addition to TS.

References

Introduction

In our previous article, we discussed the process of live transcoding from TS (Transport Stream) to MXF (Material eXchange Format) using ffmpeg, while addressing the issue of loose audio/video sync. In this article, we will provide a Q&A section to address some of the common questions and concerns related to this solution.

Q: What is the purpose of using ffmpeg for live transcoding?

A: ffmpeg is a powerful and flexible tool for video and audio processing. It provides a wide range of features and options for live transcoding, including support for multiple input and output formats, as well as advanced features such as audio/video synchronization and error handling.

Q: Why is loose audio/video sync a problem in live transcoding?

A: Loose audio/video sync can cause issues with the playback of the transcoded video, including audio and video desynchronization, which can lead to a poor viewing experience. In addition, loose audio/video sync can also cause issues with the synchronization of the audio and video streams, which can lead to errors and corruption of the transcoded video.

Q: How does the synchronization mechanism work in the live transcoding solution?

A: The synchronization mechanism in the live transcoding solution uses the timestamp of the TS stream to synchronize the audio and video streams during the transcoding process. This ensures that the audio and video streams are synchronized correctly, even in the presence of loose audio/video sync.

Q: Can the live transcoding solution handle multiple input formats?

A: Yes, the live transcoding solution can handle multiple input formats, including TS, MP4, and AVI. However, the solution may require additional configuration and setup to support multiple input formats.

Q: How can I optimize the transcoding performance of the live transcoding solution?

A: There are several ways to optimize the transcoding performance of the live transcoding solution, including:

  • Using a high-performance EC2 instance: Using a high-performance EC2 instance, such as a c5.2xlarge instance, can improve the transcoding performance of the solution.
  • Optimizing the ffmpeg configuration: Optimizing the ffmpeg configuration, such as by adjusting the bitrate and resolution, can improve the transcoding performance of the solution.
  • Using a caching mechanism: Using a caching mechanism, such as a caching layer, can improve the transcoding performance of the solution by reducing the number of times the transcoding process needs to be executed.

Q: How can I implement error handling in the live transcoding solution?

A: There are several ways to implement error handling in the live transcoding solution, including:

  • Using a try-catch block: Using a try-catch block can catch and handle errors that occur during the transcoding process.
  • Using a logging mechanism: Using a logging mechanism can log errors and exceptions that occur during the transcoding process.
  • Using a retry mechanism: Using a retry mechanism can retry the transcoding process in case of errors or exceptions.

Q: Can the live transcoding solution be used in a production environment?

A: Yes, the live transcoding solution can be used in a production environment. However, it is recommended to thoroughly test the solution in a non-production environment before deploying it in a production environment.

Conclusion

In this article, we have provided a Q&A section to address some of the common questions and concerns related to the live transcoding solution from TS to MXF using ffmpeg. We hope that this article has provided valuable information and insights to help you implement and optimize the live transcoding solution in your production environment.

References