mp4 file changes size during playback
Mathieu Duponchelle
mathieu at centricular.com
Wed Dec 4 19:01:59 UTC 2019
Here's the relevant section, 5.2 table 2 (sorry for the formatting):
Value of nal_unit_type | Description | Video elementary stream (sample entry ʹavc1ʹ or ʹavc2ʹ) | Video elementary stream (sample entry ʹvc3ʹ or ʹavc4ʹ) | Parameter set elementary stream
7Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â | SPS (..)Â Â Â | No If parameter set elementary stream is not used, SPS | Yes Parameter set elementary stream shall not be used | Yes
                      |            | shall be stored in the Decoder Specific Information | |
On 12/4/19 7:45 PM, Mathieu Duponchelle wrote:
> I'm afraid I don't have these documents available to me anymore (pretty sure I got them at some point).
> Perhaps someone else will read this and lend you their copy :)
>
> On 12/4/19 7:03 PM, David Ing wrote:
>> Mathieu --
>>
>> Please excuse the inadequacy of my google-fu. I am having trouble finding any kind of authoritative reference document which describes avc1, 2, 3, 4, ... (and the subtle differences between them)
>>
>> * My best guess is that avc1 refers to the first amendment:Â Â https://www.iso.org/standard/67318.html
>> * My best guess is that avc3 refers to the third amendment:Â Â https://www.iso.org/standard/69728.html
>>
>> Also -- I am a bit surprised that we need to pay in order to view documents like this. Does anyone know if there is a way to view this stuff for free?
>>
>> On Wed, Dec 4, 2019 at 9:14 AM Mathieu Duponchelle <mathieu at centricular.com <mailto:mathieu at centricular.com>> wrote:
>>
>> That's an interesting file, but I'm not sure it is a a compliant one:Â the resolution change is
>> advertised through SPS in the bitstream, but the MP4 header says "avc1", which as far as I remembe
>> means the H264 bitstream should not contain any SPS (please double check this, haven't looked at the spec).
>>
>> Ideally, the tool you produced this file with would use an "avc3" stream format, and not hold
>> any parameter sets in its MP4 header. That way, you could detect resolution changes by simply
>> plugging a demuxer and a parser together and looking for new caps. Currently you can only do that
>> either by also plugging a decoder afterwards and looking for caps changes, or analysing the SPS
>> manually :)
>>
>> Best,
>>
>> --
>> Mathieu Duponchelle · https://www.centricular.com
>>
>>
>> On 12/3/19 10:50 PM, David Ing wrote:
>>> I have an mp4 file which changes size during playback. But I noticed that gst-discoverer-1.0 does not report the fact that the size changes.
>>>
>>> I have two questions.
>>>
>>> 1. In theory, what is the fastest way to scan the file to determine where the size changes?
>>> 2. In practice, what is the easiest way (given the current state of gstreamer) to scan the file and determine where the size changes?
>>>
>>> Here is the file which changes size during playback:
>>>
>>> https://drive.google.com/drive/folders/1f4pGNDhzCvsg1xXWj4y9DS3vXkaglOvZ?usp=sharing
>>>
>>> Here is the gst-discoverer-1.0 output:
>>>
>>> $ *gst-discoverer-1.0 -v screencap.m4v *
>>> Analyzing file:///home/ding/mess/repro/screencap.m4v
>>> Done discovering file:///home/ding/mess/repro/screencap.m4v
>>>
>>> Topology:
>>> Â container: video/quicktime, variant=(string)iso
>>> Â Â video: video/x-h264, stream-format=(string)avc, alignment=(string)au, level=(string)4.2, profile=(string)main, codec_data=(buffer)014d402affe1002b674d402a965402a835f35602d40404050000030001000003003ce060007d0000030177009a9503b4244d4001000468ce3520, width=(int)996, height=(int)632, pixel-aspect-ratio=(fraction)1/1, framerate=(fraction)30/1, interlace-mode=(string)progressive, chroma-format=(string)4:2:0, bit-depth-luma=(uint)8, bit-depth-chroma=(uint)8, parsed=(boolean)true
>>> Â Â Â Tags:
>>> Â Â Â Â video codec: H.264 / AVC
>>> Â Â Â Â bitrate: 309812
>>> Â Â Â Â datetime: 2019-11-01T17:40:33Z
>>> Â Â Â Â title: n/a
>>> Â Â Â Â container format: ISO MP4/M4A
>>> Â Â Â
>>> Â Â Â Codec:
>>> Â Â Â Â video/x-h264, stream-format=(string)avc, alignment=(string)au, level=(string)4.2, profile=(string)main, codec_data=(buffer)014d402affe1002b674d402a965402a835f35602d40404050000030001000003003ce060007d0000030177009a9503b4244d4001000468ce3520, width=(int)996, height=(int)632, pixel-aspect-ratio=(fraction)1/1, framerate=(fraction)30/1, interlace-mode=(string)progressive, chroma-format=(string)4:2:0, bit-depth-luma=(uint)8, bit-depth-chroma=(uint)8, parsed=(boolean)true
>>> Â Â Â Additional info:
>>> Â Â Â Â None
>>> Â Â Â Stream ID: 14c5bd3783191c8af25f30b00a879f8f7bdaa4367c8ecbd954b38e5367507175/001
>>> Â Â Â Width: 1350
>>> Â Â Â Height: 846
>>> Â Â Â Depth: 24
>>> Â Â Â Frame rate: 30/1
>>> Â Â Â Pixel aspect ratio: 1/1
>>> Â Â Â Interlaced: false
>>> Â Â Â Bitrate: 309812
>>> Â Â Â Max bitrate: 0
>>>
>>> Properties:
>>> Â Duration: 0:00:34.861322222
>>> Â Seekable: yes
>>> Â Live: no
>>> Â Tags:
>>> Â Â Â video codec: H.264 / AVC
>>> Â Â Â bitrate: 309812
>>> Â Â Â datetime: 2019-11-01T17:40:33Z
>>> Â Â Â title: n/a
>>> Â Â Â container format: ISO MP4/M4A
>>>
>>>
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>>
>>
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