A CDR file records a phone call or video session

A CDR file is a digital recording of a phone call, video call, or conference session. CDR stands for Call Detail Record or, in some contexts, Call Data Record. The file captures the audio (and sometimes video) of the conversation and stores it as a computer file you can play back later.

You'll most often see CDR files in business settings. Phone systems, video conferencing software, and call centers create them automatically when calls happen. Some personal devices and apps also generate CDR files if you have recording enabled. The file itself is usually small for audio-only calls but can be much larger if it includes video.

CDR files are not the same as call logs. A call log is just a record that a call happened — who called, when, and how long it lasted. A CDR file is the actual recording of what was said and seen during that call.

Key Takeaways

  • A CDR file is a recording of a phone or video call stored as a single computer file that you can open and play back.
  • CDR files are created automatically by phone systems, video conferencing platforms, and call center software when calls are made.
  • Audio-only CDR files are usually small (a few megabytes), but video recordings take up much more storage space.
  • You can open a CDR file with media player software, though the exact program depends on what format the file is stored in.
  • CDR files are often kept for compliance, training, or dispute resolution in business and professional settings.

Where CDR files come from

CDR files are created by the software or hardware that handles the call. If you use a business phone system like Cisco, Avaya, or a cloud-based service such as Zoom or Microsoft Teams, that system can be set to record calls automatically. When recording is turned on, every call (or every call in a certain department or with certain people) gets saved as a CDR file.

Call centers almost always create CDR files. They use them to train staff, review customer interactions, and settle disputes about what was said during a call. Some personal devices and apps — like certain Android phone recorders or Skype — can also save calls as CDR files if you turn on recording before the call starts.

The person or organization running the system decides whether recording happens. In many places, recording a call without telling the other person is illegal, so businesses usually announce that calls are being recorded or get permission first.

What format a CDR file uses

CDR files can be saved in several different audio or video formats. The most common are WAV (uncompressed audio), MP3 (compressed audio), M4A (compressed audio used by Apple devices), and MP4 (video with audio). Some older phone systems use proprietary formats that only their own software can open.

The format matters because it determines what program you need to play the file. A WAV or MP3 file opens in almost any media player — Windows Media Player, VLC, iTunes, or your phone's built-in player. An M4A file usually needs iTunes or a compatible app. A proprietary format might only open in the phone system's own software.

If you receive a CDR file and are not sure what format it is, right-click the file (or long-press on a phone) and look at the file extension — the letters after the dot. That tells you what format it is and what program to try first.

How large CDR files are

An audio-only CDR file from a one-hour phone call is usually between 30 and 100 megabytes, depending on the audio quality and compression. A 10-minute call might be 5 to 15 megabytes. These sizes are small enough to email or store on any modern computer.

Video CDR files are much larger. A one-hour video call can be 500 megabytes to several gigabytes. If you need to store many video recordings, you will run out of space quickly on a regular hard drive. Many organizations keep video CDR files on a dedicated server or cloud storage service instead of on individual computers.

Why businesses keep CDR files

Call centers and customer service departments use CDR files to review how staff handled calls. A supervisor can listen to a recording to see whether the agent followed procedures, treated the customer fairly, or made a mistake. This is called quality assurance.

CDR files are also kept for legal protection. If a customer claims they were promised something during a call, or if a dispute arises about what was discussed, the recording is proof of what actually happened. Banks, insurance companies, and healthcare providers are often required by law to keep call recordings for a set period.

Training is another reason. New employees can listen to recordings of experienced staff to learn how to handle difficult calls or common questions. Some companies also use recordings to improve their processes — they listen to many calls to spot patterns in what customers ask about or complain about.

How to open and play a CDR file

If the CDR file is in a common format like MP3, WAV, or M4A, you can open it with any media player. On Windows, right-click the file and choose "Open with," then select Windows Media Player, VLC, or another player you have installed. On a Mac, double-click the file and it should open in iTunes or the default media player. On a phone, tap the file and choose a music or media app.

If the file is in a format your player does not recognize, you may need to convert it. Free online tools like CloudConvert or Zamzar can convert audio files from one format to another. Upload the CDR file, choose the format you want, and download the converted file.

If the CDR file came from a proprietary phone system, you might need that system's own software to open it. Ask the person or department that gave you the file what program to use. They can usually provide the software or convert the file to a standard format like MP3 for you.

Privacy and legal issues with CDR files

Recording a call without the other person's knowledge is illegal in many places. Some states and countries require both people on a call to agree to recording (called "two-party consent"), while others only require one person to know (called "one-party consent"). Before you record a call, check the laws where you live and where the other person lives.

If you work for a company that records calls, that company is usually responsible for following the law, not you. But if you are recording a personal call, you need to know the rules. In the United States, federal law allows one-party recording, but California, Florida, Illinois, Pennsylvania, and a few other states require both parties to consent.

CDR files that contain personal information — like health details, financial account numbers, or social security numbers — should be treated as sensitive. Many organizations encrypt them or store them on secure servers. If you have a CDR file with private information, do not share it casually or leave it where others can access it.

Frequently Asked Questions

Can I open a CDR file on my phone?

Yes, if the file is in a common format like MP3 or M4A. Download the file to your phone and tap it to open it in your default music or media player. If it is in an uncommon format, you may need to convert it first using an online tool or ask the person who sent it to convert it for you.

What is the difference between a CDR file and a voicemail?

A voicemail is a message someone left for you when you did not answer. A CDR file is a recording of a conversation that happened between two or more people. Voicemails are usually shorter and stored by your phone carrier. CDR files are created by the software handling the call and can be much longer.

How long do companies usually keep CDR files?

It varies by industry and law. Banks and financial companies often keep them for seven years. Healthcare providers may keep them for six years or longer. Call centers might keep them for 30 days to a few years depending on their policy. Check with your company or the organization that created the file to find out how long they store recordings.

Can I delete a CDR file from my phone system?

That depends on your role and your company's policy. In most cases, only administrators or compliance officers can delete recordings. If you need a file deleted, contact your IT department or the person who manages your phone system. Be aware that many organizations are required by law to keep recordings, so deletion requests may be denied.

What if I receive a CDR file and cannot open it?

First, check the file extension to see what format it is. If it is MP3, WAV, or M4A, try a different media player — VLC is free and opens almost any audio format. If it is a proprietary format, ask the person who sent it what software you need or request that they convert it to MP3 for you.