The most frequent errors detected during media file analysis
Deep analysis of the video file is often necessary to identify the cause of broadcasting errors, to check and configure encoding equipment, and to test how video codecs work. To do this, experts use professional video analyzing tools. Such analyzers help to find artifacts in video and check various video parameters such as resolution, buffer, IDR-frames, etc. If something is wrong with the video, the user gets a message. However, sometimes it is difficult to understand what these errors mean and identify their cause.
This article presents the description of the most frequent errors that could be found during media file analysis.
Most frequent errors
Decoding error
The frame cannot be decoded correctly because syntax errors occur.
There are some visible artifacts during playback.
The error is caused by problems on the encoder side. Check the encoder settings and its operation.
Coding Unit parsing error
It occurs when the decoder cannot correctly decode the Coding Unit (CU).
Decoder cannot decode the slice or the frame correctly as well as slices and frames predicted from the current one. There are some visible artifacts during playback.
The error is caused by data loss during the content broadcasting. Check QoS parameters of the input stream.
CPB overflow
Such type of errors occur when Coded Picture Buffer (CPB) is overflowed during compression.
The encoder does not maintain a specified rate control (it does not keep an HDR model), that is why it cannot compress a complicated video scene.
Possible broadcasting problems: errors of the components that are sensitive to bit rate (multiplexer, DVB/ATSC modulator); heavy increase in bit rate and higher network load; unsteady broadcasting.
Possible playback problems: artifacts; missed frames in case a decoder have a fixed buffer size, which is less than required for a stream.
The error is caused by poor encoder configuration or encoding errors.
Adjust encoding equipment configuration, and tune encoder settings for the specified rate control.
CPB underflow
Such type of errors occur when Coded Picture Buffer (CPB) is underflowed during compression.
The encoder does not maintain a specified rate control (it does not keep an HDR model), that is why it cannot compress a simple video scene, or the encoder has not received input data.
Possible broadcasting problems: errors of the components that are sensitive to bit rate (multiplexer, DVB/ATSC modulator), jerky broadcast.
Possible playback problems: a decoder may play back a video sequence with jerks.
The error is caused by poor encoder configuration or encoding errors.
Adjust encoding equipment configuration, and tune encoder settings for the specified rate control.
Changes
There are changes in the stream:
• Resolution is changed;
• Profile is changed in the encoder settings;
• Level is changed in the encoder settings;
• Entropy coding mode is changed;
• Chroma format is changed.
This kind of changes in the stream may lead to a critical error on the decoder side, and the player will stop playback with an error.
The problem is caused by errors in the encoder configuration in splicer or playout systems. It is necessary to bring the settings to a unified form.
The first access unit of each coded video sequence shall be an IDR access unit
The error occurs when a video sequence does not start from an IDR frame.
Possible playback problems: the decoder waits for the next key I frame from which it can play back the stream correctly.
The problem may be detected in the stream recording or in the media file prepared for VOD service. If the problem is detected in the stream recording, there is no error: the beginning of the recording may not coincide with an IDR frame. If the problem is detected when analyzing the media file, this is a major error: the media file must start with an IDR frame.
In this case, check and adjust the encoder settings.
Invalid parameter values
Cabac_init_idc shall be in the range of 0 to 2, inclusive
The cabac_init_idc parameter value is not in the specified range.
Playback problems: the decoder cannot decode the content.
The problem is caused by an error on the encoder side.
Nuh_layer_id > 0 is not supported by the version of decoder
Values of nuh_layer_id exceeding 0 indicate presence of additional video layers in the stream, decoding of which is not supported by the current decoder version. For example, it might be an alpha channel.
Possible playback problems: decoder either ignores all layers not equal to 0 or there are artifacts during playback.
The problem is caused by decoder functionality and/or encoder configuration.
H.264/AVC parameters
Seq_parameter_set_id shall be in the range of 0 to 31, inclusive
Pic_parameter_set_id shall be in the range of 0 to 255, inclusive
The seq_parameter_set_id and pic_parameter_set_id parameter values for H.264/AVC video sequences are not in the specified range.
Playback problems: the decoder cannot initiate decoding.
The problem is caused by an error on the encoder side.
Sequence parameter set with id equal to seq_parameter_set_id not found
No seq_parameter_set_id pair with identical values in the SPS and PPS headers was found in an H.264/AVC video sequence.
Playback problems: the decoder cannot initiate decoding.
The problem is caused by an error on the encoder side.
H.265/HEVC parameters
Sps_seq_parameter_set_id shall be in the range of 0 to 15, inclusive
Pps_pic_parameter_set_id shall be in the range of 0 to 63, inclusive
Slice_pic_parameter_set_id shall be in the range of 0 to 63, inclusive
The values of sps_seq_parameter_set_id, pps_pic_parameter_set_id, slice_pic_parameter_set_id parameters for H.265/HEVC video sequences are not in the specified range.
Playback problems: the decoder cannot initiate decoding.
The problem is caused by an error on the encoder side.
Not found sequence parameter set with pps_seq_parameter_set_id
No sps_seq_parameter_set_id and pps_seq_parameter_set_id pair with identical values is found in the H.265/HEVC video sequence.
Playback problems: decoder cannot initiate decoding.
The problem is caused by an error on the encoder side.
Not found picture parameter set with slice_pic_parameter_set_id
No slice_pic_parameter_set_id and pps_pic_parameter_set_id pair with identical values are found in the H.265/HEVC video sequence.
Playback problems: decoder cannot initiate decoding.
The problem is caused by an error on the encoder side.
In this article we have described the most common errors encountered when analyzing media files. However, the full list of errors is much longer.
If you do not find any particular error message here, it means that the problem is more complicated, and it is necessary to scrutinize the stream parameters to determine its cause.
All illustrations of error messages in this article were made in Elecard StreamEye, a professional product for video quality analysis that is part of StreamEye Studio.