[FFmpeg-devel] [PATCH 1/4] libavcodec/adts_header: add frame_length field and avpriv function to parse AAC ADTS header

["zhilizhao(赵志立)"]

> On Aug 16, 2021, at 11:19 AM, James Almer <jamrial at gmail.com> wrote:
> 
> On 8/16/2021 12:08 AM, "zhilizhao(赵志立)" wrote:
>>> On Aug 16, 2021, at 2:25 AM, Nachiket Tarate <nachiket.programmer at gmail.com> wrote:
>>> 
>>> These will be used by HLS demuxer in case of sample decryption.
>>> 
>>> Signed-off-by: Nachiket Tarate <nachiket.programmer at gmail.com>
>>> ---
>>> libavcodec/adts_header.c |  1 +
>>> libavcodec/adts_header.h | 14 ++++++++++++++
>>> libavcodec/adts_parser.c | 32 ++++++++++++++++++++++++++++++++
>>> 3 files changed, 47 insertions(+)
>>> 
>>> diff --git a/libavcodec/adts_header.c b/libavcodec/adts_header.c
>>> index 0889820f8a..e4454529c4 100644
>>> --- a/libavcodec/adts_header.c
>>> +++ b/libavcodec/adts_header.c
>>> @@ -66,6 +66,7 @@ int ff_adts_header_parse(GetBitContext *gbc, AACADTSHeaderInfo *hdr)
>>>     hdr->sample_rate    = avpriv_mpeg4audio_sample_rates[sr];
>>>     hdr->samples        = (rdb + 1) * 1024;
>>>     hdr->bit_rate       = size * 8 * hdr->sample_rate / hdr->samples;
>>> +    hdr->frame_length   = size;
>>> 
>>>     return size;
>>> }
>>> diff --git a/libavcodec/adts_header.h b/libavcodec/adts_header.h
>>> index f615f6a9f9..9ecd67fb5b 100644
>>> --- a/libavcodec/adts_header.h
>>> +++ b/libavcodec/adts_header.h
>>> @@ -34,6 +34,7 @@ typedef struct AACADTSHeaderInfo {
>>>     uint8_t  sampling_index;
>>>     uint8_t  chan_config;
>>>     uint8_t  num_aac_frames;
>>> +    uint32_t frame_length;
>>> } AACADTSHeaderInfo;
>>> 
>> The patch can be separated into two patches.
>>> /**
>>> @@ -47,4 +48,17 @@ typedef struct AACADTSHeaderInfo {
>>>  */
>>> int ff_adts_header_parse(GetBitContext *gbc, AACADTSHeaderInfo *hdr);
>>> 
>>> +/**
>>> + * Parse the ADTS frame header contained in the buffer, which is
>>> + * the first 54 bits.
>>> + * @param[in]  buf  Pointer to buffer containing the first 54 bits of the frame.
>>> + * @param[in]  size Size of buffer containing the first 54 bits of the frame.
>>> + * @param[out] phdr Pointer to pointer to struct AACADTSHeaderInfo for which
>>> + * memory is allocated and header info is written into it.
>>> + * @return Returns 0 on success, -1 if there is a sync word mismatch,
>>> + * -2 if the version element is invalid, -3 if the sample rate
>>> + * element is invalid, or -4 if the bit rate element is invalid.
>>> + */
>>> +int avpriv_adts_header_parse(AACADTSHeaderInfo **phdr, const uint8_t *buf, size_t size);
>>> +
>>> #endif /* AVCODEC_ADTS_HEADER_H */
>>> diff --git a/libavcodec/adts_parser.c b/libavcodec/adts_parser.c
>>> index 5c9f8ff6f2..32489dadf4 100644
>>> --- a/libavcodec/adts_parser.c
>>> +++ b/libavcodec/adts_parser.c
>>> @@ -42,3 +42,35 @@ int av_adts_header_parse(const uint8_t *buf, uint32_t *samples, uint8_t *frames)
>>>     return AVERROR(ENOSYS);
>>> #endif
>>> }
>>> +
>>> +int avpriv_adts_header_parse(AACADTSHeaderInfo **phdr, const uint8_t *buf, size_t size)
>>> +{
>>> +#if CONFIG_ADTS_HEADER
>>> +    int ret = 0;
>>> +    GetBitContext gb;
>>> +
>>> +    if (size < AV_AAC_ADTS_HEADER_SIZE)
>>> +        return AVERROR_INVALIDDATA;
>>> +
>>> +    if (!*phdr)
>>> +        *phdr = av_mallocz(sizeof(AACADTSHeaderInfo));
>>> +    if (!*phdr)
>>> +        return AVERROR(ENOMEM);
>> I’m not keen about such design, that
>> 1. you can allocate AACADTSHeaderInfo directly
>> 2. if you don’t, I will allocate it for you
>> I’m not sure about the rule of avpriv_ part, in my opinion, the struct should
>> always allocated by libavcodec and used by libavformat. libavformat shouldn’t
>> allocate it on stack or heap by itself for ABI compatibility.
> 
> It's copying the behavior of avpriv_ac3_parse_header(), which may be a remnant from a time where it was called from within libavcodec itself.
> I agree it should not be allowed to pass a pre-allocated struct by another library for ABI compatibility reasons, but the only user Nachiket is adding is letting lavc allocate it, so it's not that important.

The commit message says: "These will be used by HLS demuxer in case of sample decryption.” I thought it will be used by libavformat.

> 
>>> +
>>> +    ret = init_get_bits8(&gb, buf, AV_AAC_ADTS_HEADER_SIZE);
>>> +    if (ret < 0) {
>>> +        av_free(*phdr);
>>> +        return ret;
>>> +    }
>>> +
>>> +    ret = ff_adts_header_parse(&gb, *phdr);
>>> +    if (ret < 0) {
>>> +        av_free(*phdr);
>> av_freep(phdr)
>>> +        return ret;
>>> +    }
>>> +
>>> +    return 0;
>>> +#else
>>> +    return AVERROR(ENOSYS);
>>> +#endif
>>> +}
>>> -- 
>>> 2.17.1
>>> 
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